Possibly the end of The Big Bang Theory? (Not the TV show)
September 16, 2013 11:21 AM   Subscribe

Nature covers a brane based theory of cosmological creation... Is the universe a 3D brane created from a 4D star collapsing into a black hole?

Arxiv link (PDF) for the DGP paper....

Days like these I wish I was a physicist. Probably why my attempts at world domination always fail.
posted by Samizdata (110 comments total) 29 users marked this as a favorite
 
...the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole...

But where did the 4D star's universe come from? A 5D black hole in a more meta-universe? So instead of turtles all the way down, it's multidimensional stars all the way up?
posted by sammyo at 11:26 AM on September 16, 2013 [18 favorites]


This kind of stuff makes my brane hurt.

Thank you! Good night! *mic drop*
posted by Rock Steady at 11:27 AM on September 16, 2013 [14 favorites]


As much as I should accept that maybe the universe is complicated, I always get the feeling reading current physical pronouncements that we should all be armed with Occam's razor...
posted by njohnson23 at 11:29 AM on September 16, 2013 [2 favorites]


I always get the feeling reading current physical pronouncements that we should all be armed with Occam's razor...

"A wizard did it." It's extremely simple.
posted by Dark Messiah at 11:30 AM on September 16, 2013 [14 favorites]


Days like these I wish I was a physicist. Probably why my attempts at world domination always fail.

Biotech. Go for an unstoppable army of mutant geckoes or mind-control plague, or a neural interface for a supercomputer, ensuring you, and not some machine without the biochemical ability to gloat over vanquished enemies or lust after conquest, are the beneficiary of singularity. Or all of the above.
posted by Slap*Happy at 11:30 AM on September 16, 2013


Someone light the physicsmattsignal.
posted by jquinby at 11:31 AM on September 16, 2013 [10 favorites]


I know there are some science-y types who will probably read this, so:

I did read the linked article, but could someone explain "four dimensional star" to me in simple language suitable for the childlike? I have just barely gotten my head around "and in this universe the fourth dimension is time" and this whole other-universe-with-more-dimensions thing is failing to work for me.
posted by Frowner at 11:31 AM on September 16, 2013 [2 favorites]


And we can see further evidence of this in the presence of two-dimensional universes created by stellar collapse, distributed more or less randomly and floating through our own 3D space. Some extraterrestrial civilizations may, in theory, have the ability to access these two-dimensional universes, using them to sink waste heat from macrostellar structures like Dyson Spheres, to dispose of toxic materials, or even as places to safely banish undesirables, e.g., Krypton's Phantom Zone.
posted by Naberius at 11:39 AM on September 16, 2013 [6 favorites]


I love physics! It's like science fiction with better math.
posted by Perfectibilist at 11:45 AM on September 16, 2013 [14 favorites]


(PDF link fixed. Ain't the staff here awesome?)
posted by Samizdata at 11:45 AM on September 16, 2013 [1 favorite]


We do need to remember that the map is not the territory. Some things in the world are very hard to describe (math is the way of description) the very tiny subatomic, and the very large. Look at a map, it tells us a lot but now that it's flat a straight line from NYC to London appears to be a curve. Both the globe and the flat image are projections of something greater that we are unable to perceive, or that is just imaginary. Or maybe just do some hand wavy pointing in the direction of height, width, length, tesser.
posted by sammyo at 11:45 AM on September 16, 2013


Is the universe a 3D brane created from a 4D star collapsing into a black hole?

Well, obviously
posted by Hoopo at 11:46 AM on September 16, 2013 [3 favorites]


And we can see further evidence of this in the presence of two-dimensional universes created by stellar collapse, distributed more or less randomly and floating through our own 3D space. Some extraterrestrial civilizations may, in theory, have the ability to access these two-dimensional universes, using them to sink waste heat from macrostellar structures like Dyson Spheres, to dispose of toxic materials, or even as places to safely banish undesirables, e.g., Krypton's Phantom Zone.

I think this is sarcasm but maybe it shouldn't be. Does this finding imply that stellar collapse in our 3D universe can produce a 2D Flatland universe?
posted by justsomebodythatyouusedtoknow at 11:46 AM on September 16, 2013


could someone explain "four dimensional star" to me

I think what they're proposing is that the same way that a 2D circle has a surface that is a 1D circumferential line, and a 3D sphere has a 2D surface the way you can make a flat map of the surface of the Earth, the expanding "hypersphere" of stuff left by a 4D star exploding would have a surface that's like a 3D space, which is what our universe might be. So a spatial fourth dimension that's analogous to height, width, and depth rather than a time-like fourth dimension.

Edwin Abbot's book Flatland: A Romance of Many Dimensions^ is the classic explanation of what fourth and higher spatial dimensions might be like. It's about a hundred pages when published as a paperback, so a quick read, and it's free because it's from the 19th century - links to several different editions available on the web in the Wikipedia article.
posted by XMLicious at 11:47 AM on September 16, 2013 [5 favorites]


This is awesome if only because it validates intuitions my non-physicist self used to have back when I was following this field of science more closely and enthusiastically.

But where did the 4D star's universe come from? A 5D black hole in a more meta-universe? So instead of turtles all the way down, it's multidimensional stars all the way up?

In a way, this sort of just brings us back to what had been the standard scientific view for many years (and incidentally the view that Einstein held), which is that the universe as a whole is eternal and infinite (so-called Steady-State Theory).

It's funny, but people seem to forget that Big Bang theory was originally championed at least in part by religiously-minded scientists who believed that Big Bang theory left wiggle room for divine intervention (which it was thought might be found in those mysterious, theoretically unknowable moments before the Big Bang itself).

This isn't so much a new theory about the universe's origins as it is an acknowledgment that the evidence for Big Bang theory doesn't necessarily mean what proponents interpreted it to mean. Personally, I've still yet to see any evidence that there's any reason to assume the universe conforms to our cognitive biases for understanding the world in terms of finite narratives.
posted by saulgoodman at 11:47 AM on September 16, 2013 [2 favorites]


Slap*Happy: "Days like these I wish I was a physicist. Probably why my attempts at world domination always fail.

Biotech. Go for an unstoppable army of mutant geckoes or mind-control plague, or a neural interface for a supercomputer, ensuring you, and not some machine without the biochemical ability to gloat over vanquished enemies or lust after conquest, are the beneficiary of singularity. Or all of the above.
"

Well, I do realize the importance of vanquishing THEN gloating. Leaving a potential enemy alive so I can cackle about their failure is the number one failure of potential world dominators. The more you know...
posted by Samizdata at 11:47 AM on September 16, 2013


You can't really visualise a four dimensional sphere because our brain isn't wired to comprehend anything beyond three dimensions. Nobody can, not even top notch scientists. The way they go about it is with math and stuff.

So basically you have the 1-sphere, which is just a circle.

Then you have a 2-sphere, the surface of a ball, which is a 1-sphere projected onto an axis, like a cylinder, although both ends are squeezed so the whole thing looks the same regardless of where you look at it from.

The 3-sphere is a 2-sphere projected the same way. I'll be honest with you, I'm already lost at that point. Suffice to say a 3-sphere is a volume, whereas a 2-sphere is a surface.

So from there you start getting an idea of what a 4-sphere is, or a four dimensional sphere would be. It's a 3-sphere, or space, projected on a 4th dimension.

It's always been very difficult for most people to accept the fact that our 3D universe wasn't embedded in anything, that there isn't an outside. So I guess what this theory is saying is there is something beyond the 3-sphere universe.
posted by surrendering monkey at 11:50 AM on September 16, 2013 [2 favorites]


Potheads have been saying this for years.
posted by Foci for Analysis at 11:54 AM on September 16, 2013 [18 favorites]


saulgoodman: "It's funny, but people seem to forget that Big Bang theory was originally championed at least in part by religiously-minded scientists who believed that Big Bang theory left wiggle room for divine intervention (which it was thought might be found in those mysterious, theoretically unknowable moments before the Big Bang itself)."

I would love to hear more about this. Post it here or memail me if you'd rather.
posted by boo_radley at 11:55 AM on September 16, 2013 [1 favorite]


Did a hyper-black hole spawn the Universe?

Betteridge's law would dictate that this is not the case.
posted by brundlefly at 11:56 AM on September 16, 2013 [3 favorites]


As Sammyo says the map is not the territory. I assume that physicists are examining the territory and then trying to map it some way. But I get the feeling that they are looking at the territory through some maps that color how they pick and choose what they emphasize in their descriptions. Brane theory is a popular map courtesy of string theory. My question lies in where in the multiple layers of abstraction are we looking in these new physical descriptions. Are we talking about the territory or are we just discussing a map?
posted by njohnson23 at 11:58 AM on September 16, 2013 [1 favorite]


A 4 Dimensional sphere is a mathematical model of a ball that would shrink from infinity before snapping back toward expansion; a 4D star, therefore, would be a cosmic supergiant that would alternately collapse and expand upon itself, before it would ultimately rupture. Which would mean the "Big Bang" was a mind-boggingly huge gamma-ray burst that resulted in a 3D brane of flung superstellar matter that would effectively serve as the event horizon for an enormous black hole. This would fit in with the observance of near uniformity within the examined cosmos' temperature, and may explain why the universe is perceived to be expanding at a rapid rate.
posted by Smart Dalek at 12:00 PM on September 16, 2013 [3 favorites]


Oh gosh it's like a fractal picture of a turtle, look deeper and there's real turtles walking along those spirals, and each one has a picture of fractal turtles on it's back, and you zoom in again and go quietly mad.
posted by sammyo at 12:01 PM on September 16, 2013 [4 favorites]


Wouldn't a 4-spatial-dimensional spacetime that was capable of having stars in it, with their own supernovae and core collapses, imply an entire second level of fine-tuning and the assorted naturalness problems? In fact, it feels like a fourth dimension would require even greater fine-tining to have stars.
posted by Mitrovarr at 12:02 PM on September 16, 2013


"It could be time to bid the Big Bang bye-bye."

No, it's not.
posted by Ivan Fyodorovich at 12:04 PM on September 16, 2013


Well, heck, here's a reprinted article from no farther back than 1991 talking about how athiests might be able to build arguments against Big Bang theory to counter the creationist interpretations of the theory that were the norm at the time:
The idea that the big bang theory allows us to infer that the universe began to exist about 15 billion years ago has attracted the attention of many theists. This theory seemed to confirm or at least lend support to the theological doctrine of creation ex nihilo. Indeed, the suggestion of a divine creation seemed so compelling that the notion that 'God created the big bang' has taken a hold on popular consciousness and become a staple in the theistic component of 'educated common sense'. By contrast, the response of atheists and agnostics to this development has been comparatively lame. Whereas the theistic interpretation of the big bang has received both popular endorsement and serious philosophical defence (most notably by William Lane Craig and John Leslie1), the nontheistic interpretation remains largely undeveloped and unpromulgated.
posted by saulgoodman at 12:04 PM on September 16, 2013 [4 favorites]


Biotech. Go for an unstoppable army of mutant geckoes or mind-control plague, or a neural interface for a supercomputer, ensuring you, and not some machine without the biochemical ability to gloat over vanquished enemies or lust after conquest, are the beneficiary of singularity.

Score!!! Uh, I mean, how 'bout them red birds!
posted by Kid Charlemagne at 12:04 PM on September 16, 2013


Is the universe a 3D brane created from a 4D star collapsing into a black hole?

No, of course not. Don't be so silly.
posted by Devonian at 12:04 PM on September 16, 2013


boo_radley: To amplify a bit on saulgoodman's comment: One of the original big-bang-like models was developed by Georges Lemaître, who was a Catholic priest. However, I would not say that the main proponents of the Big Bang theory when it was being argued about most (around the 1950's) were doing so from a religious standpoint -- atheists were prominent in their ranks -- but rather that the opposition to it was often anti-religious in its inspiration. That opposition dominated the field until the cosmic microwave background radiation, the afterglow from when the universe was hot and dense in the past, was discovered and understood in the 1960's, and you'll still find people who are trying to figure out ways around having a Big Bang in part to avoid having a beginning.
posted by janewman at 12:07 PM on September 16, 2013 [4 favorites]


The fact that we can't (for the most part) visualize spaces with more than three dimensions means nothing to math, where these objects are well-understood.
posted by thelonius at 12:11 PM on September 16, 2013 [1 favorite]


I have just barely gotten my head around "and in this universe the fourth dimension is time" and this whole other-universe-with-more-dimensions thing is failing to work for me.

Temporal and spatial dimensions are different things. A 4-spatial dimension is easiest to understand by analogy, comparing a square to a cube and then applying those relationships to a cube to understand how a hypercube might be explained. Here's a video, for example, showing a rotating hypercube, but, since it's only a 3-D projections (well 2-D with implied 3-D) what you're really seeing is, essentially the shadow of a rotating hypercube. All of the angles should remain 90° at all times (which is, of course, not possible in three dimensions). There are a bunch of other 4-D rotation models on YouTube if you poke around.

The thing to remember is that the models are all rigid and being rotated. Their apparent change in shape is just their 3-D shadow resulting from their rotation in 4 space. An analogy would be a cube casting a six pointed shadow when held at the right angle.
posted by Kid Charlemagne at 12:14 PM on September 16, 2013 [3 favorites]




So the article suggests the physicists behind this theory are tweaking the model to fit inflation data. That sounds dodgy, but my main question is: What about this is testable?
posted by Blazecock Pileon at 12:16 PM on September 16, 2013 [1 favorite]


Devonian: No, of course not. Don't be so silly."

The disinformation campaign from Big Brane has begun.
posted by vanar sena at 12:16 PM on September 16, 2013


My brain don't understand branes.
posted by slogger at 12:17 PM on September 16, 2013 [1 favorite]


Pretty much the idea that there has ever been a "nothing" or void for the universe to be created from has always been a religious one, IMO.

and you'll still find people who are trying to figure out ways around having a Big Bang in part to avoid having a beginning.

And to avoid having to hand-wave away whatever inexplicable miracle occurred in the moments preceding the Big Bang, which the theory essentially renders unknowable by definition, and to avoid positing some creation ex nihilo event since it's not a particularly powerful scientific explanation to say the universe just appeared out of nowhere somehow for no reason.
posted by saulgoodman at 12:19 PM on September 16, 2013 [2 favorites]


"Pretty much the idea that there has ever been a 'nothing' or void for the universe to be created from has always been a religious one, IMO."

This is a preoccupation of yours that doesn't reflect the reality of the history of cosmology.
posted by Ivan Fyodorovich at 12:22 PM on September 16, 2013 [6 favorites]


Wouldn't a 4-spatial-dimensional spacetime that was capable of having stars in it, with their own supernovae and core collapses, imply an entire second level of fine-tuning and the assorted naturalness problems? In fact, it feels like a fourth dimension would require even greater fine-tining to have stars.

No one on this thread so far has claimed to be competent to interpret the underlying research. Knowing a little mid-20th century physics isn't going to cut it. I suggest we hold off on trying to apply or shoot down theistic fine tuning arguments at least until someone who knows what they're talking about provides us with at least a crude sketch of a layman's understanding of what's going on here and what it implies.

I think we have to assume that our intuitions are really, really not good guides to interpreting this material.
posted by justsomebodythatyouusedtoknow at 12:23 PM on September 16, 2013 [2 favorites]


I've often wondered whether a dolphin with echolocation, or a human who had somehow acquired a detailed echolocation sense or become able to directly sense the output of a radar for example, would be better able to envision 4D space because they're accustomed to directly experiencing three dimensions and the internal density of objects, as opposed to our optical sense of vision where the 3D world is collapsed down to a 2D image with depth perception jury-rigged on top of it.

* Post-world-domination note to self: put out someone's eyes and have them wired up to a radar. Also, dolphin physicists. *
posted by XMLicious at 12:24 PM on September 16, 2013 [5 favorites]


This is a preoccupation of yours that doesn't reflect the reality of the history of cosmology.

Duh. That's why I wrote "IMO." But, you know, Cosmology's roots are in religious creation myths. The earliest cosmologists just had very crude tools for doing the science and tried to reason to their conclusions from first principles.
posted by saulgoodman at 12:25 PM on September 16, 2013


As to this specific paper: we talked about it in our journal club last week, and the reception was skeptical. I'd say there are two significant red flags (one of which Blazecock Pileon just alluded to):

1) The theory of inflation (a key component of current Big Bang models) predicts that the original fluctuations in density in the Universe shortly after the Big Bang should have about, but not exactly, equal strength at all scales (i.e., if you express the pattern of density as a sum of lots of waves - basically, a Fourier expansion, for those familiar with the term - the amplitude of waves with wavelength L will on average be be about the same as those with wavelength 2L or L/2). This model predicts that there should be exactly equal strength at all scales. Current observations (from the Planck satellite) are almost, but not exactly, equal in strength at all scales, and reject the "scale-invariant" prediction from this paper at ~5 sigma significance. This is a strike against this theory, as the authors recognize.

2) The theory relies on a DGP formulation of gravity, and there's significant evidence that DGP is wrong (even for the 'normal' branch -- the new paper only refers to work that rejects the 'self-accelerating' version of the DGP theory, which would have provided a dark energy effect for free, but see e.g. Lombriser et al. 2009, here, for problems with the 'normal' version too).

One other thing that didn't help its reception: the reference to 'white holes' in the paper's title immediately set off everyone's BS-sensors. It's a common trope in nonspecialists' theories of everything. However, I (and others) know Niayesh Afshordi, at least, and he's not a kook, so we gave that a pass.
posted by janewman at 12:30 PM on September 16, 2013 [11 favorites]


Does this finding imply that stellar collapse in our 3D universe can produce a 2D Flatland universe?

I don't pretend to understand any of this stuff, so maybe someone else can comment on whether it's relevant, but that sounds a bit like the holographic principle.
posted by XMLicious at 12:35 PM on September 16, 2013


For me, the interesting part is not that this might "disprove" Big Bang so much as that it would put the observable effects of whatever that event was in a context that doesn't require a Creation Ex Nihilo event (which, regardless of any real merits as a cosmological concept, is also very much one of the core tenets of the Abrahamic religions, including Christianity. I'm always a little embarrassed when I see Christians attacking Big Bang theory on religious grounds when in fact it really seems to be their best bet for a scientific view that still leaves open the possibility of divine intervention).
posted by saulgoodman at 12:39 PM on September 16, 2013 [1 favorite]


- Let there be light.
- Let there also be infra-red.
- Let there be ultra-violet as well.
- Let there be radio waves, microwaves, and also X-Rays, as well as Gamma-Rays.
- Scrap that.
- Let there be electromagnetic radiations.
- Let there be electromagnetic waves powerful enough so that they create quarks, gluons and electrons when light particles collide, which might not happen so often.
- Let there be positrons and anti-quarks too, and let them annihilate when they collide with electrons and quarks, respectively, to generate more photons.
- Let there be neutrons and protons forming from quarks and gluons, and let the proton be billion of orders of magnitude more stable than the neutron.
- Let there be neutrinos, W and Z bosons.
- Let there be a Higgs Field, which is non-zero so as to give a mass to fermions, as well as most bosons, but not all of them.
- Let there be neutrinos, and make them elusive.
- Let there be dark matter, and make it even more elusive.
- Let there be dark energy, which will make the fabric of space grow exponentially.

And God saw the photons, the positrons, the quarks, the neutrinos, the W and Z bosons, the Higgs field, the dark matter and the dark energy, and it was good.
posted by surrendering monkey at 12:39 PM on September 16, 2013 [14 favorites]


The holographic principle is definitely involved here, XMLicious: The paper's title is in fact "Out of the White Hole: A Holographic Origin for the Big Bang".
posted by janewman at 12:39 PM on September 16, 2013 [1 favorite]


Braaaaaaaaaanes
posted by Mister_A at 12:40 PM on September 16, 2013 [4 favorites]


The Bloom Toroidal Model of the Universe predicts another big bang within 1.68 billion years.
posted by xowie at 12:40 PM on September 16, 2013 [1 favorite]


Dark Messiah: "I always get the feeling reading current physical pronouncements that we should all be armed with Occam's razor...

"A wizard did it." It's extremely simple.
"

all facts begin as dreams dreamt by a wizard. if the wizard crosses the path of a scorned widow, then he shares it at the town council. then it is a hypothesis. and it's time to drown the wizard. if he floats, he is an evil wizard and must be burned alive, if he drowns the hypothesis is true!
posted by symbioid at 12:40 PM on September 16, 2013 [3 favorites]


Perfectibilist: "I love physics! It's like science fiction with better math."

Chemistry is like science fiction with better Meth.
posted by symbioid at 12:42 PM on September 16, 2013 [2 favorites]


saulgoodman: Lots of current theories have a Big Bang for our local universe but place it within a larger, and enduring, landscape/multiverse -- so avoiding 'creation ex nihilo' would be far from unique to this theory.

Basically, these ideas tend to start with a quantum fluctuation within the larger multiverse that causes a portion of it to start inflating. That portion is our universe (which may end up with different laws of physics than other inflating bubbles). One inspiration for these ideas is Heisenberg's uncertainty principle: one consequence of it is that you can borrow energy from the universe so long as you do it for a short amount of time. The net energy of our universe is very close to zero (gravity's negative potential energy balances out the mass-energy of everything else), so you might be able to borrow for a quasi-infinite period.

This gets pretty wild pretty quick -- e.g., our own universe could give birth to new universes via quantum fluctuations, too.
posted by janewman at 12:47 PM on September 16, 2013 [4 favorites]


brundlefly: "Did a hyper-black hole spawn the Universe?

Betteridge's law would dictate that this is not the case.
"

"Is Betteridge's law always a valid rule to apply to headlines?"
posted by symbioid at 12:47 PM on September 16, 2013 [3 favorites]


(I call that symbioid's formulation of Betteridge, aka: Meta-Betteridge)
posted by symbioid at 12:48 PM on September 16, 2013 [3 favorites]


PS One of the amazing things about working in cosmology is that it is a field that is simultaneously ancient in its origins, but only very young as a science. Through most of the twentieth century, cosmology was primarily discussed in philosophy, not physics, departments. It's really only in the seventies that the field started to grow (thanks in no small part to Jim Peebles' efforts; he cannot get too much credit for the rise of physical cosmology). By the 1980's, it was beginning to thrive, and its growth has continued through the present.
posted by janewman at 12:53 PM on September 16, 2013 [3 favorites]


(I call that symbioid's formulation of Betteridge, aka: Meta-Betteridge)

I'll forever be the Elisha Gray to your Alexander Graham Bell when it comes to re-formulation of Betteridge's law!
posted by TwoWordReview at 12:55 PM on September 16, 2013 [1 favorite]


So string theory has had something similar as part of it's model for some time, called the Ekpyrotic theory, that also involves multidimensional branes. How is this different and/or better?
posted by CheeseDigestsAll at 12:57 PM on September 16, 2013


CheeseDigestsAll: I'm far from an expert on brane scenarios. My impression, though, is that the ekpyrotic scenario identifies Big Bangs with periodic collisions between a couple of branes (one of which corresponds to our Universe); while in this scenario the trigger for a Big Bang is the collapse of a supernova within a 4d 'higher' universe (I share Mitrovarr's skepticism above about how sure we are that such events should happen, given that we can barely model supernovae in 3d now).

tl;dr: I think the main similarity to the ekpyrotic scenario is just that both rely on a brane picture of the Universe, but the processes are completely different.
posted by janewman at 1:08 PM on September 16, 2013


"I love physics! It's like science fiction with better math."

Chemistry is like science fiction with better Meth


Biology is like science fiction with better Moth?

Futurology is like science fiction with better Myth?

Speech-language Pathology is like science fiction with better Mith?

*drops mic*
posted by blue_beetle at 1:08 PM on September 16, 2013 [4 favorites]




> A 4 Dimensional sphere is a mathematical model of a ball that would shrink from infinity before snapping back toward expansion.

That absolutely isn't the case - you're misunderstanding the classical visualization of a 4-d sphere, and in two different ways. :-/

A 4-sphere doesn't grow or shrink. If you passed a 3-sphere ("a ball") through a 2-space ("a plane") you'd first see nothing, then a circle which would increase until its diameter was the ball's diameter, and then start to shrink again and finally vanish - but the 3-sphere wouldn't be changing size.

You'd get the same effect if you passed a 4-sphere through 3-space ("real space"). You'd see nothing, then a point expanding to a ball of the same diameter as the 4-sphere, and then back down to nothingness.
posted by lupus_yonderboy at 1:21 PM on September 16, 2013 [7 favorites]


Does this mean that 4-dimensional stars are brane food?
posted by alms at 1:23 PM on September 16, 2013


"I love physics! It's like science fiction with better math."

Chemistry is like science fiction with better Meth

Biology is like science fiction with better Moth?

Futurology is like science fiction with better Myth?

Speech-language Pathology is like science fiction with better Mith?


Elephantology is like science fiction with better Musth.
posted by Rock Steady at 1:29 PM on September 16, 2013


Mining skill in fantasy games is like metallurgy with better mithril?
posted by symbioid at 1:30 PM on September 16, 2013


Eating fancy cereal is like breakfast with Bircher muesli?
posted by jquinby at 1:31 PM on September 16, 2013 [1 favorite]


I went on this so-called 4D ride at Busch Gardens Williamsburg, and while it was fun, it was really just like a scarier, faster version of the Haunted Mansion ride at Disney World, with the addition of 3D glasses.

I did see cool skeleton knights and werewolves, but I was not driven insane by impossible geometries and inconceivable vistas, and don't even get me started on the 3D projections of vast, shambling, unholy 4D monstrosities, of which there were none...
posted by Mister_A at 1:31 PM on September 16, 2013 [3 favorites]


I went on a sweet 4D escheresque ride (more of a walk, really) up stairs in my house, but I had eaten 1/4 oz of p. cubensis mushrooms.
posted by symbioid at 1:33 PM on September 16, 2013


I did see cool skeleton knights and werewolves, but I was not driven insane by impossible geometries and inconceivable vistas, and don't even get me started on the 3D projections of vast, shambling, unholy 4D monstrosities, of which there were none...

That's because you weren't wearing the 4D glasses.
posted by no relation at 1:33 PM on September 16, 2013 [1 favorite]


so avoiding 'creation ex nihilo' would be far from unique to this theory.

True. I know there are other alternatives that also do this, but it seems to me none of them have gotten much traction. If this one does, and can be verified, that'd be neat.
posted by saulgoodman at 1:40 PM on September 16, 2013


BTW how is Garrett Lisi fairing these days?
posted by Mei's lost sandal at 1:46 PM on September 16, 2013 [1 favorite]


Those interested in 4D and other dimensionalities might enjoy these two books:

Flatterland: Like Flatland, Only More So by Ian Stewart
Spaceland: A Novel of the Fourth Dimension by Rudy Rucker
posted by Ivan Fyodorovich at 1:51 PM on September 16, 2013 [2 favorites]


Turns out The Soft Boys were right all along: Hear My Brane.

"Maybe you'll remember. Maybe you'll forget. It doesn't matter very much -- it hasn't happened yet."
posted by the matching mole at 1:57 PM on September 16, 2013


So when a 3D star collapses into a black hole, does it form a 2D universe? That explains comic books.
posted by oneswellfoop at 2:00 PM on September 16, 2013 [1 favorite]


> And God saw the photons, the positrons, the quarks, the neutrinos, the W and Z bosons, the Higgs field, the dark matter and the dark energy, and it was good.

And after a very long while, God saw life and declared, "Huh! That was a freebie!" And it was a bit of a mixed bag.
posted by gilrain at 2:22 PM on September 16, 2013 [5 favorites]


If you ask what the Big Bang is you'll get some disagreement. I've rewritten this comment a fair few times now, but basically if you make a straw man Big Bang model and claim that's what the Big Bang is, I'm not going to be very surprised if you pull the rug out from under it.

If you claim you've pulled the rug out from under what I think the Big Bang is, then I'm going to be spitting beer all over my keyboard, down the internet pipes and back out of your screen all over your face.
posted by edd at 2:31 PM on September 16, 2013 [1 favorite]


I did read the linked article, but could someone explain "four dimensional star" to me in simple language suitable for the childlike? I have just barely gotten my head around "and in this universe the fourth dimension is time" and this whole other-universe-with-more-dimensions thing is failing to work for me.
This is not my type of science, but I think it's possible to achieve a somewhat more intuitive understanding of four dimensions without using time. Time is just so different from other dimensions to our brains that it's extremely difficult to think of it as another dimension unless you're used to the equations, I think. Instead, I think we can turn to pop culture for better inspiration.

We've all seen Ghost, right? Imagine two different worlds, the real physical world, and a ghost world. The ghosts can pass through all of our matter, and we can pass through the ghosts. But we're all Whoopi Goldberg and can see and hear the ghost world. (Also, imagine that ghosts can't pass through each other, they bump into each other in the ghost dimension, just as objects in our dimension bump into each other). The ghost world is a 3D world, just as our world is a 3D world, we're just all overlapping. Also, imagine that you can flip between the two, you can jump into the ghost world in order to get by a wall in the physical world, then jump back into the real world in the same "spot" to interact with physical matter. This is a "discrete" dimension, there's room for both ghost material and real material at each point in space. The switch between real and ghost is completely different than any direction in our 3D world, it's at a "right angle" to all the usual three space dimensions, but I never found the "right angle" terminology useful since we're not directly observing it.

Now, instead of just the two types of real material and ghost material, imagine that there's an entire color spectrum of types of matter. The color spectrum has an order like a rainbow, ROYGBIV and all that. Two objects of different colors pass through each other, but two objects of the same color bump into each other. Movement along the axis of this fourth dimension consists of changing color along the spectrum. You can go from green smoothly through cyan to blue, but you can't just jump from green to violet, just as you can't suddenly move your hand from your mouse to your keyboard without hitting everything in between. So to press the keys on your keyboard, you first need to change the color of your finger tips to match the color of the keys, otherwise your fingers would go right through. If you want to tie your shoe but your desk is in the way, you shift your body to any color that's not in your desk (perhaps violet?) and then you can bend right through it, then shift your finger tips to a color that's in your shoelaces in order to be able to manipulate your shoelaces. Distance is a matter both of inches, but also of color-shifting. In this analogy, color forms a continuous fourth dimension, an entirely different axis of existence separate from the normal three directions that we're used to for the physical world. And by not using time as the fourth dimension, you can more easily imagine movement, and normal dynamics for objects as our brains think about them.

Not sure if this is helpful for you, but it's how I tend to think about these things. Also, I'm thinking that the hypothesized 4D star would still be embedded in time somehow, so the star is really in 5D space-time, as the occurrence of "5D" in the arXiv abstract implies. (Or is that 5D referring to some other nomenclature?) Perhaps a physicist who knows the linked material better could describe this particular piece.
posted by Llama-Lime at 2:31 PM on September 16, 2013 [19 favorites]


Potheads have been saying this for years.

LINDSAY: What if all of this is a dream, and it isn't even our dream, it's that dog's dream? Maybe we're just existing in his mind and all of a sudden he'll go drink out of the toilet and we'll be gone. What will happen to us if that dog wakes up? It will be over.

MILLIE: Life is not that dog's dream.
posted by nathancaswell at 2:36 PM on September 16, 2013 [3 favorites]


"Meta-Betteridge"

I love their potato chips!
posted by klangklangston at 2:38 PM on September 16, 2013 [1 favorite]


I just finished John Barrow's The Origin of the Universe (1994) a couple nights ago. In it, he says:
Remarkably, universes with 3 large dimensions of space are very special. If there are more than 3 large dimensions, no stable atoms can exist.
Then later in talking about the unlikelihood of life existing in a higher dimensional universe
... because of the absence in additional large dimensions of any structures (like atoms) bound together by electromagnetism and the strong nuclear force.
If this is so, how could a 4-D star exist? What would it consist of? Maybe not so much a star as just a gravitational collapse of protons/neutrons?
posted by DarkForest at 2:42 PM on September 16, 2013 [1 favorite]


"This is not my type of science, but I think it's possible to achieve a somewhat more intuitive understanding of four dimensions without using time. Time is just so different from other dimensions to our brains that it's extremely difficult to think of it as another dimension unless you're used to the equations, I think. Instead, I think we can turn to pop culture for better inspiration."

I have a buddy who's doctorate was in combinatorics, specifically matrix combinatorics, and any popular description of "dimensions" drives him nuts — to him, a dimension is pretty much anything that can be a row or column in a matrix, so things like color, temperature, charge, conductivity, mass, anything can be another "dimension." (The most recent rant was spurred by some ad here promising a 5-D amusement park ride.)
posted by klangklangston at 2:47 PM on September 16, 2013


"The fact that we can't (for the most part) visualize spaces with more than three dimensions means nothing to math, where these objects are well-understood."

A vast majority of mathematical objects have no direct physical manifestation.
posted by idiopath at 2:59 PM on September 16, 2013


For instance, a normal ol' assumed-to-be-perfect 3D sphere.
posted by gilrain at 3:08 PM on September 16, 2013


(Although we've tried!)
posted by gilrain at 3:09 PM on September 16, 2013 [1 favorite]


janewman: However, I (and others) know Niayesh Afshordi, at least, and he's not a kook, so we gave that a pass.

You know cosmology is in a difficult spot when solid work is hard to tell apart from the latest kook to wander on to arXiv. Although this is the whole basis of ArXiv vs SnarXiv, so that's nothing new or really cosmology-specific, I guess.
posted by RedOrGreen at 3:11 PM on September 16, 2013 [1 favorite]


klangklangston, I get where your friend is coming from, but think your friend's issue with the usage of the word "dimension" isn't so much about popular misconceptions as it is about personal taste, or differences in usage between people of different backgrounds.

I'm in computer graphics, and it sounds like I probably use "dimension" in about the same way your friend does. When I try to talk to my physicist grandfather about my work, though, I have to be careful with my terminology. When I say "dimension", I'm thinking of an element in a vector (or a dimension of a state space), but he thinks of a dimension of physical space. When I say "tensor", I'm thinking of a multilinear operator, but he thinks of a tensor field. When I talk about my work in translating physics simulations from high-dimensional to low-dimensional descriptions, he thinks of something like Kaluza-Klein theory, but I'm thinking of something ... well, not at all like that.
posted by Serf at 3:29 PM on September 16, 2013 [2 favorites]


And God saw the photons, the positrons, the quarks, the neutrinos, the W and Z bosons, the Higgs field
"The little bastards will never find that one!"
posted by Wolfdog at 4:05 PM on September 16, 2013 [2 favorites]


I wonder how this idea interacts with Strings and Quantum Bohemian Gravity?
posted by zengargoyle at 4:16 PM on September 16, 2013 [3 favorites]


This is an illustration of where mathematical models can run amok.

Every kind of model has its limits. Bohr, for example, envisioned atoms as a nucleus of positively charged protons and neutral neutrons, with orbiting electrons. The model works well because it's something people can grasp. But the model has its limits, and there are many aspects of quantum behavior that cannot be explained by the Bohr model. The model is still useful because it does lead to many accurate scientific predictions.

A newer mathematical model, quantum mechanics, seeks to be even more accurate in its predictions than Bohr's model. It succeeded in many ways, and like the Bohr model, has led to many interesting discoveries. But it too has its limits.

In pure mathematics, exceeding three dimensions is effortless. Calculations involving four or more dimensions can easily be solved. But just because the mathematical model can do it, doesn't mean that the physical reality it attempts to model, can also do it. A model is designed to represent reality, but it is not itself reality. I suspect that all such mathematical models of the universe, which point to other dimensions, will eventually be shown to be purely mathematical.
, from a similar thread on Slashdot, a few days ago. Other interesting comments in the forum.

This stuff is always fascinating, nevertheless!

Probably, the late, great scientist J.B.S. Haldane had it right, and said it all - i.e.
Haldane: "I have no doubt that in reality the future will be vastly more surprising than anything I can imagine. Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose."
posted by Vibrissae at 4:23 PM on September 16, 2013 [3 favorites]


Yay! An energetic discussion on one of my posts!
posted by Samizdata at 4:37 PM on September 16, 2013


Yes, excellent post & discussion. A few others, perhaps we should work at "Science Mondays" on MiFi?
posted by sammyo at 5:00 PM on September 16, 2013


Someone light the physicsmatt signal.

0. CTRL + F
1. No physicsmatt comment
2. On to next post
posted by clarknova at 5:26 PM on September 16, 2013 [2 favorites]


I feel that dimensionality is not a property of space but something that describing space necessitates. In other words, space doesn't have three dimensions, but our descritption of space uses three dimensions.
posted by Jode at 5:28 PM on September 16, 2013


"Not sure if this is helpful for you, but it's how I tend to think about these things."

Why don't you think about it mathematically and physically, because it's math and physics? It's entirely possible to get much closer to comprehension than with your strange analogy if you think about what dimensionality is with two and three dimensions and then extrapolate from that. You don't have to guess how a 4D object would appear to a 3D observer, it's entirely knowable. This isn't poetry, this is math.

I'd like to recommend, again, Stewart's Flatterland.

"1. No physicsmatt comment
2. On to next post"


I hear ya. But there's been two at least two astronomers who've posted in this thread, one of them an actual cosmologist. Physicsmatt is a particle physicist, I believe.
posted by Ivan Fyodorovich at 6:27 PM on September 16, 2013 [2 favorites]


I feel I should expand on my earlier comment.

In biology there is a well established theory that suggests given a single organism how you can evolve an entire diverse biosphere from it (Darwin's theory of evolution by natural selection of course). It doesn't explain where that single organism came from. That is handled separately by some other theory of abiogenesis. That could be any of a range of fairly mundane ideas (basically chemical accident in the right conditions) to wackier ones (such as life came from space).

In cosmology, there is a well established idea based on how we already understand physical laws about how you reach the current universe from a much earlier hotter and denser state (the Big Bang theory). It doesn't explain why there is that particular kind of hot, dense (and very low entropy) state in the first place. Unfortunately in this case it's possible to naively wind back the clock past the regime where we think those physical laws should work but still try to apply them, and go too far back and ultimately hit a singularity. Most theoretical physicists take that as an indication that you tried to apply the idea outside the bounds of its applicability, and you really shouldn't be doing that, and you should be thinking about the appropriate kind of 'abiogenesis' theory to put in place at that point. It might be 4D supernovae, the aforementioned ekpyrotic scenario, some eternal inflation idea, or whatever. Unlike biology, all the ideas probably qualify as pretty wacky, and none as all that mundane unfortunately. However, coming up with a new idea, just like coming up with a new kind of abiogenesis, doesn't invalidate the later evolution.

The success of the Big Bang as a model is all about the later evolution. Suggesting an alternative beginning doesn't invalidate it, just because you replace the part where you might naively over-extend the theory. You're just replacing an explanation you basically already knew could not be right. The useful bit of the Big Bang as a model is left completely intact, just like changing the details of the last common ancestor in biology leaves Darwinian evolution intact.

That's why a breathless 'It could be time to bid the Big Bang bye-bye.' gets my goat a bit. These are adjustments (very important adjustments to make, admittedly) to just the earliest parts of the model which leave everything that makes the Big Bang a great success completely intact (or at least mostly intact with slight changes, which will hopefully turn out to be somewhat observable so you can actually do science to check if the idea is right).
posted by edd at 7:20 PM on September 16, 2013 [10 favorites]


Sorry guys, my family is visiting today, and so I missed the physicsmatt signal. I'm working on a comment on this, but it's not going to be finished tonight, so you'll have to wait till tomorrow. Terrible, I know, but science and sarcastic remarks don't write themselves.

Also, people should consider reading the rest of the scientists here: edd, RedorGreen, and janewman. They do know what they are talking about.
posted by physicsmatt at 7:26 PM on September 16, 2013 [1 favorite]


Thanks for the endorsement, physicsmatt !

I'd strongly second edd's comment -- this new model ends up with a universe in much the same state we'd expect at the end of an inflationary epoch, and everything would proceed much the same (though not precisely, due to the differences between DGP gravity and General Relativity) after that. It's less 'invalidating the Big Bang theory' than providing a different possible beginning to the Big Bang story.

If anything, so far as I can tell the predictions this model does make (perfect scale invariance -- though the authors are looking for outs there -- and DGP gravity) are already in tension with observations, so at least the naive version of the model is probably already ruled out.

The good news is that ideas for experiments that would be able to detect direct evidence for inflation under a wide range of scenarios do exist, and would be technically feasible around 2020 or so (see the inflation white paper on this page for details - other white papers there provide a good summary of the current state and near future of cosmology).

If such an experiment doesn't detect anything it wouldn't prove that inflation (a key component of standard Big Bang models) is wrong, but it would at least rule out many of the simplest variations of the theory, which would widen the search for alternatives. Someone'll need to find ~$100 million under their couch cushions for that to happen, though.
posted by janewman at 8:07 PM on September 16, 2013 [2 favorites]


Thanks for the clarifications and this thread. Hope I wasn't being cross or obtuse in my comments. Of course BB is correct, as far as it goes. But without theoretical contexts to understand the event, it's just a random, inexplicable accident. So it's cool to see developments in this field. Not educated enough anymore to judge these ideas on their merits, but I hope some ideas like this eventually stick and hold up to experimental/mathematical scrutiny.
posted by saulgoodman at 8:31 PM on September 16, 2013


This reminds me of the comic Buckminster Fuller drew about the notion that the Big Bang and Steady State theories pale in comparison to his theory that the universe began solely for the purpose of enabling Woody Allen's existence.
posted by BiggerJ at 9:57 PM on September 16, 2013


This would make perfect sense if black holes were magic. But they aren't. They are just big balls of gravity. Because they have so much mass that light can't escape, they just look like magic from our perspective.

This is what Einstein has been trying to tell us for years: there IS a reality, it just LOOKS different depending on where you are.

Another internet armchair physics pet peeve of mine: arguing with people who confuse really fast with instantaneous. The speed of light is really fast. It might even be the speed limit of the universe. But that doesn't create causation paradoxes; light still takes time to travel. The light I see from a distant star seems like it is happening now, but only because I am a dumb animal who can only witness it from one perspective. A far off observer could see the light get emitted, travel for millions of years, and then land in my eyeballs.
posted by gjc at 4:28 AM on September 17, 2013


In order to try and read this article, I first went to the wikitrons to try and figure out what a brane was. (I'm liberal arts, this stuff does not come naturally to me...) And I got like 3 lines in and hit "The variable p refers to the number of spatial dimensions of the brane. That is, a 0-brane is a zero-dimensional pointlike particle, a 1-brane is a string, that can either be open or closed, a 2-brane is a "membrane", etc. Every p-brane sweeps out a (p+1)-dimensional world volume as it propagates through spacetime."

I feel about that the same way I feel about foreign languages that are close to ones I know some of. I recognize the word patterns, I can puzzle some meaning out of the first few parts thanks to high school geometry (points! lines! planes! I got this!), but by the end we're into some advanced verb tenses that are only used in formal written language that I saw once fifteen years ago and so I can see the infinitive (probably...) but for the actual nuance -- isn't the fourth dimension time, and there are more? there are infinity more? how can we have more? what is there to have more from? so confused now.

So, Llama-Lime - that color-dimension keyboarding explanation was brilliant, and lupus_yonderboy, your spheres passing through other spheres were also really helpful. I don't think I'm up to really grasping the science yet, but at least you guys gave me the 501 Physics Verbs so I can try.
posted by sldownard at 4:57 AM on September 17, 2013 [2 favorites]


It kind of seem to me like this is just a big bang of another sort. For us ignorant Luddites, the big bang theory is any theory that suggests that the universe was created at all and that cosmic background radiation and red shift of light are the evidence! The end of the big bang theory to me would look like some discovery that there was no creation of the universe at all...say if someone figures out that background radiation and red shift are due to distance and an intrinsic property of the vastness of space rather than actual expansion...or something.
posted by BearClaw6 at 6:36 AM on September 17, 2013


sldownard: I won't claim to know much about branes (they're generally pretty irrelevant to what we're able to observe, so I leave it to the string theorists to figure them out and then report back when they finally have useful results). However, I can, I think, at least partially explain the statement that "Every p-brane sweeps out a (p+1)-dimensional world volume as it propagates through spacetime."

Consider the surface of a sphere (a balloon, the Earth, etc. -- they're all close enough to spheres for our purpose). That surface is two-dimensional: i.e., you can specify location on the sphere with two coordinates (e.g., latitude and longitude). However, it is embedded in a three-dimensional space (which contains the earth/balloon/etc.). If the 'host' sphere moves you could describe the region swept out by the surface over time, but you'd need three dimensions to describe that shape, not two.

This idea, at least, is more relevant than it might seem. Our universe could have the same geometry as the three-dimensional surface of a four-dimensional sphere (don't try to draw it :) ), though it would have to be one of exceedingly large radius, much larger than the observable universe, to be consistent with observations. Here's where it gets confusing: you'd naturally then think that there's a four-dimensional 'space' our Universe is embedded in, but that's not actually necessary in general relativity. I.e.: our universe can be 'curved' like the surface of a sphere even if there's not an extra dimension to curve around.

P.S. One thing that leads to confusion is people talking about time as a dimension, so e.g., they might say that we live in four dimensions of space-time. To avoid these problems, physicists often will use terms like "3+1 dimensional space", because time can be interrelated to, but still works differently from, space.

P.P.S. In case you didn't notice: the name p-brane was not chosen accidentally...
posted by janewman at 7:19 AM on September 17, 2013 [4 favorites]


janewman already said most of the specific things that should be said about this paper, and again, my parents were here last night visiting so I'm not reading this paper in detail right now. Instead, let's all pull up a chair and talk about the Big Bang: what it is, what it isn't, and why it's not something equivalent to either religion or that bullshit you came up with while you were stoned.

The Universe* today is expanding in every direction we look. For galaxies outside our Local Group (which is gravitationally bound together), they are receding from us in every direction we look. Using careful measurements and a lot of clever work, we've found that the further away an object is, the faster it recedes. This is known as Hubble's Law, and the rate at with things recede is Hubble's Constant H. Best measurements are H = 70 km/s/megaparsec or so; which is to say, for every million parsecs an object is away (1 parsec = 3.26 lightyears), it is moving an additional 70 km/s away from us.

*I'm usually very careful about my capitalization, and here it matters. The Big U Universe is THE particular universe in which we live. Not to be confused with any other universe in which we don't live. Just as our Milky Way Galaxy is a big G Galaxy, and all others are galaxies.

The way to interpret this not that we're in the center of everything, but we are living in a Universe in which the fundamental distance between objects is increasing. That is, the "metric," the way we measure how apart things are, is stretching with time. The usual analogy is take a balloon and blow it up halfway. Then paint a bunch of dots on the balloon and blow it up the rest of the way. Any particular dot sees all other dots move away from it, but not dot is in the center of the balloon: the center of the balloon is in a direction other than on the surface. In the same way, the center of the Universe is back in time.

So, if everything is moving apart, running time backwards makes everything get closer together. If you take an air pump and compress it, it heats up. The Universe does the same: as we run the clock backwards, everything gets closer together, and the average temperature should increase. Right now, if you look in any direction, you see a bath of low temperature photons at microwave wavelengths, corresponding to a temperature of about 2.7 kelvin (that's -270 C) with a variation of less than 1 part in 10^5 (I'll come back to those variations later, they're important). This is the cosmic microwave background (CMB); it's the cooling remnants of the very hot bath of photons that filled the Universe back when it was very very hot.

At some point, the Universe was hot enough that electrons could not remain bound to the atomic nuclei, so the Universe was filled with a plasma of electrons and charged nuclei, along with photons being continually absorbed by the charges and re-emitted. As the Universe cooled, the electrons finally had low enough energy to bind with the nuclei (mostly hydrogen, a sizable chunk of helium, and some trace amounts of lithium and beryllium) and the Universe became electrically neutral. When this happened, all the photons that just had been emitted didn't get reabsorbed, and they just flew off in a straight line forever afterwards. So when we look at the CMB, we are looking at a snapshot of the "surface of last scattering," and it's a picture of the Universe when it was about 300,000 years old. This age corresponds to a "redshift" z = 1100 or so; this redshift means that every photon in the CMB is 1/(1100+1) as energetic as it was when it was emitted, and has a wavelength 1100+1 times bigger (z = 0 is defined as today, thus that extra +1 floating around). This decrease in energy is due to the expansion of the Universe; today the Universe is 1100+1 times larger than it was at the surface of last scattering. This CMB is one of the pieces of evidence that demonstrates that the Universe used to be hotter and denser than it is now, along with the Hubble expansion. It also is a prediction of physics that we have understood for maybe 100 years. Nothing about the relevant microphysics is not well documented.

Running the clock back further, before the surface of last scattering, the nuclei are still ionized, and the temperature just keeps increasing as we go back in time. Eventually, the average temperature is so high that the nuclei themselves melt. Rather than being bound into protons and neutrons, the quarks and gluons are free-streaming in the "quark gluon plasma." Running the clock forward from this moment, as the Universe cools the quarks and gluons condense into protons and neutrons, and then, before the neutrons decay (with a half-life of 11 minutes), any element heavier than hydrogen (a single proton) must be formed. This is called Big Bang Nucleosynthesis (BBN); it occurs between ~0.1 second and ~10^3 seconds (say 20 minutes) after whatever it is we're calling the Big Bang (I'll get there soon). This is where helium, heavier isotopes of hydrogen, lithium, and beryllium are formed. All the heavier elements are actually born many millions of years later in the cores of the first stars.

Again, this is a prediction of the expanding Universe/hot dense beginning model. The physics behind it are more complicated than the CMB physics, but after our nuclear program of the 40's and 50's, we actually know a great deal about how nuclei can form (and actually, from experiments at the RHIC collider in Brookhaven and the heavy ion runs at the LHC, we have created quark gluon plasmas on Earth, getting us back to the conditions of the early Universe once again). Therefore, we can predict with reasonable accuracy the percentages of each element that should be formed. Then, we have to go look for places in the Universe that have "primordial abundances," places where the elements have not been processed through stars. It's tricky, but we think we have it down reasonably good, and the predictions match observations (incidentally, the only way the predictions match is if there's something called "dark matter," which we had suspected existed from other measurements. Dark matter affects the rate of expansion of the Universe, but is not protons or neutrons, and so doesn't play a role in BBN directly. The amount needed to match BBN predictions is exactly the amount needed to match other orthogonal observations).

That's it. That's the hottest we KNOW the Universe ever got. We know BBN occurred* and so we know the Universe had an average temperature of some 100 billion K (10 MeV average thermal energy). We have no direct evidence that the Universe ever was hotter or denser. Therefore, to some degree, THIS is the Big Bang. It doesn't require the Universe to be infinitely dense, it doesn't require any physics beyond what we have experimentally discovered here on Earth, and it matches to a very high degree of accuracy our observations in multiple independent areas.

*To the degree we know anything in physics. I'm still not convinced I'm not a Boltzmann Brain dreaming the rest of you reprobates, so don't go all "what is truth" on me, man.

Now, that only gets us to BBN. We know physics at higher energies existed, so you can keep running the clock back and ask "well, now what?" We often do, or, I often do in my job as a particle physicist. If we could measure the cosmic neutrino background of neutrinos that decoupled from the thermal bath way back when (the equivalent of the CMB, but with neutrinos), we could push our direct experimental knowledge back to energies of 10's of GeV, hundreds of times higher (and thus earlier) than our present direct knowledge. When talking about dark matter, we often assume that the Universe was chugging along "in thermal equilibrium" (that is: hot and dense) at energies of 100 GeV to many TeV. But we don't KNOW that it ever was.

And if it wasn't? Well, the "Big Bang" as I think of it is still true, because the "Big Bang" in a general sense to me just means "Universe started hot and dense, and I know experimentally that it was hot and dense at some point; maybe just not as hot and dense at some earlier time as my naive backwards extrapolation takes it. If I just run my clock back to zero, then yeah, I hit infinite temperature and infinite density, but I know that there will be crazy new physics (probably involving gravity if nothing else) that kicks in before that, and I should not expect my naive extrapolation to continue to work. Weird shit will happen, and I don't know what.

So, bringing it back around to the paper under discussion, I echo all the other physicists' ire in seeing "Is the Big Bang Wrong?" flung around. To the degree we know anything in life or science, we know that "the Big Bang" in a general sense is true. We just don't know what happens in the first zeptosecond or whatever "afterwards." To some degree, I suspect we never will, because the evolution of the Universe as it cools wipes out much of our knowledge of the previous physics.

But let's talk about the possibilities anyway. There is actually a big clue as to what could be going on, lurking all around us. Think of the CMB: those photons that flew off in straight lines 13.7 billion years ago, when the Universe was 300,000 years old. When I see a CMB photon now (or, my radio telescope picks on up, more accurately), what am I seeing. Well, I'm seeing something that was traveling in a more or less straight line (gravitational lensing ignored) since that moment of decoupling. So it's not from around here. It's from WAY far away. So if I see a photon in the CMB from one direction, and then from the complete opposite direction, this is the first moment ever that those two photons where right next to each other. The places that they were born, in that cosmic soup? Those places were not next to each other; they were so far separated that light could never travel between them, simply because the Universe wasn't old enough, and light didn't have enough time to make the trip. Yet somehow, those two photons are exactly the same temperature, to with 1 part in 10^5.

Those small fluctuations, by the way, are a record of the initial gravity perturbations that will go on to form the clusters of galaxies in which all stars and planets live. Again, this is evidence of dark matter, since the photon bath exerted enough pressure to keep the atoms from falling into the gravitational wells, but dark matter, not interacting with photons, were free to start infalling and grow the perturbations. Without dark matter, the small fluctuations in the CMB would look very different, as would the distribution of galaxies and clusters in the Universe today. Go go gadget dark matter. The seeds of these perturbations however? I'll get to those

So, the Universe is very uniform, too uniform in fact. If we're just now seeing segments of the Universe that have never been "in causal contact" (meaning information, via light could have flown back and forth between them) how did the initial conditions set themselves up to arrange uniform temperature? Additionally, the Universe is very "flat" meaning in the absence of local matter density, geometry is Euclidean (triangles, for example have angles adding up to 180 degrees). If that doesn't make sense to you, grab your trusty balloon you used to exemplify the expansion of space and draw a big triangle on it. The angles will add to to more than 180. The Universe has this flatness to a very high degree of accuracy, but its again an initial condition. A Universe that is not flat to start with will get increasing "unflat" as time goes on. To be as flat as we know it to be today, it must have started REALLY flat. How? (Also, flatness is a function of the energy density of the Universe. Adding up the stuff we know about: atoms, photons and neutrinos, gets us to only 5% of flatness. We need to add in the dark matter - 25% - and something else called dark energy - 70% - to get to flat. We get those numbers not to make the Universe flat, but to match other observations. Flatness is just an added bonus).

Finally, there's another problem, which is a bit more technical. As the Universe cools, there should be "glitches" for lack of a better term, in the field values of things like the electromagnetic field. These glitches manifest as particles, in particular, magnetic monopoles (a north pole without a south, and vice versa). Now, we experimentally know there are no magnetic monopoles around. There's an experiment running in a basement lab since the 80's looking for them - there was a single possible signal in 1982 on Valentine's Day, but nothing since. The predictions from our naive expectations are that, as you cool the Universe from these very very high temperatures (higher than those of the BBN), so many monopoles should form that we'd be swimming in them. Literally, they'd cause the Universe to recollapse immediately. So how did the Universe get rid of them all?

The answer is something called inflation. The idea is that WAAAAAAAAAAAAAY before all the BBN or CMB stuff happened, there was this field, the inflaton field. This field (and everything, electrons, photons, Higgses, etc, can be described as a field in quantum field theory, so this isn't anything new) started at some incredibly high value everywhere. Why? Don't know. Just did. Bear with me. This particular configuration causes the metric of the Universe (the distance measure, remember) to "inflate:" distances between objects get very very very far apart, very very very quickly. This is actually the same thing that's happening now with dark energy: a background field is causing the metric to expand faster and faster. Just today, the effect is small, comparatively. And no, no one knows what dark energy is, or whether it's connected to inflaton field.

So the inflaton causes "the inflationary era," predating all the physics we know anything about. Some tiny patch of spacetime got REAL big, expanding to a size at least e^60 times bigger than it started (or 10^26 times larger). This means that the bits we are seeing now, the CMB photons just coming to us today, were in causal contact in the early Universe: the started right next to each other, in fact. Just they were driven apart by the inflationary epoch, and are just now getting back in contact. It also solves the monopole problem by spreading out the volume over which the monopoles are distributed (so maybe we saw one of the two monopoles left in our causal volume on Valentines Day. Ooops, there it goes....). It solves the flatness problem by expanding the metric by this huge factor: regardless of the initial curvature, a huge inflationary factor will drive it to near flatness real quick (think of it as diving in towards the Earth from space. Once you're in orbit, you see the curvature of the Earth, as you get close - effectively the Earth "getting bigger" in your reference frame - the curvature disappears and things look flat).

Now, once this inflationary epoch is done, we've expanded the Universe A LOT. And remember the analogy I used way back in the start, of an expanding air pump? You expand an air pump, the air inside gets cold. After inflation, the Universe is fucking icy. Really damn cold. No fun particles around for the CMB, BBN, Earth, New York and so on. That's a bit of a problem. But, we still have the inflaton field, and it has a huge amount of energy. The idea is, that as inflation ends, the way it ends involves the inflaton dumping energy into the rest of the particles, reheating the Universe, and then the whole story I told above kicks off.

Finally, those initial seeds we see evidence of in the CMB? Those are caused by the way that the inflaton worked, and the fact that they are nearly uniform on all scales (a technical point again) gives us some constraints on the way that any possible inflationary era could have occurred. Also, a 2nd piece of information carried by the CMB photons, the "B modes", can tell us more about an possible model of inflation. I don't know as much about this, so maybe one of my colleagues can talk about that.

But back to the bigger question. Where in that is the Big Bang? Is it the reheating? That at least is hot. Is it the inflationary era, if that existed? Well, it's earlier, so maybe that's "the Big Bang." But it's not hot and dense. It's the exact opposite, in fact. What started the inflaton? Now we can think of the bigger spacetime in which the tiny piece that got inflated resided. What happened to the patch next to our inflated bit? Did it inflate? Are it's laws of physics and field content the same? That's a separate little u universe, maybe it's the same, maybe it isn't. Are bits of our Universe inflating away right now? From the outside, we wouldn't notice. Is the inside of a black hole undergoing inflation? Is that what happened before, to us (see I knew I'd bring it around to the paper in the end)? Well, we don't know, because we lack direct experimental probes of the eras before BBN, which include reheating and inflation and any pre-inflationary physics.

It all gets a bit turtly-all-the-way down, I know. But amazingly, we're at least able to ask pointed and coherent questions now, something that we've only recently been able to do in a manner that at least reasonably resembles physics. Much of this can't yet be tested, but some of it can, and maybe we'll be a bit more clever in the future and test that which right now I can't think of how we'd test. Will we ever see if we're part of a bigger Multiverse of patches of inflating spacetimes? My guess is no, but who am I to say for sure, and the people thinking about how our Universe got to where it is find it useful often to think about that bigger set up, so let's let them run with it while it's useful.

The take away from all this is that there was "a Big Bang," if your definition of a Big Bang is "Universe started hot and dense and expanded." How hot and dense we don't know. If your definition of the Big Bang is "Universe started in an infinitely hot and dense singularity," well we don't know. My money is that it didn't start in a singularity, but again, I don't know that for sure. And thankfully, there are people who's job it is to think about that sort of thing, and maybe one day we will know.

Not me though, my job is to take on the quotidian questions of "hey, what IS dark matter anyway. And this Higgs thing? WTF?" Also: "where is my coffee?"

As a final note, how did we all miss that the physicsmatt signal is clearly The MattSignal? I also demand Mattarangs.
posted by physicsmatt at 7:24 AM on September 17, 2013 [48 favorites]


Flagged as fantastic.

Also, I'm now sitting here bemused at the thought that we started out as bipedal group predators and are now paying some of these highly specialized predators to sit around and think about how we all got here. And we're all just tiny frills on the outside of a giant balloon.

Thanks for putting some perspective on a frustrating afternoon in the office :)
posted by brokkr at 7:44 AM on September 17, 2013


The nice thing about physicsmatt's responses is that they are helpful for laypeople, but I generally learn something from them too (in this case, why we refer to the dumping of energy from the inflaton into everything else as 'reheating' the Universe, instead of just 'heating').

I can maybe flesh out his comment about CMB "B-modes". Basically, when we look at light from the CMB, we can measure not just its intensity but also its polarization -- basically, the orientation of the electric/magnetic fields of the incoming light, which tells us about the orientations of the electric/magnetic fields where the light was emitted (though modified by material along the way). In general, we'd expect the pattern of polarization on the sky to look (in a mathematical sense) like the patterns of electric field lines connecting charges. Electric fields can be described as coming from the divergence (in the mathematical sense) of another quantity (the "potential"), yielding a pattern which has zero 'curl' to it*. However, we can also check for patterns that look (again, only in a mathematical sense) like magnetic field lines, which can be described as coming from the curl of a potential (e.g., more like flowing around in a circle, rather than going inward or outward, though that's not quite it), yielding a pattern with zero divergence.

*Note: I don't think I can really explain curl well in words, but this image from Sky and Telescope shows the two sorts of patterns associated with divergence (kind of think of flow arrows going inward or outward from a source) and curl (think of flow going round and round a source).

So basically, we measure the divergence (flow in/out) and curl (flow round and round) parts of the CMB polarization pattern, and call the two pieces "E-modes" and "B-modes" by analogy with electric and magnetic field lines, just to confuse everyone (both electric and magnetic fields are involved in polarization already, after all). It turns out that almost all of the sources of polarization in CMB maps should primarily yield E-modes. The exceptions are gravitational lensing of the CMB by foreground objects -- which basically can warp E-mode patterns into B-mode ones -- and gravity waves.

In many inflation models, gravity waves would arise due to quantum fluctuations in the curvature of space (not just the density of matter); just like the disturbed surface of a pond would ripple outwards, these disturbances in the curvature of space will ripple out across space (gravitational waves sound like science fiction, but there is by now firm evidence that they must exist from studies of binary pulsar systems, even though they are too weak for us to have detected them directly yet). Gravity waves can cause a pattern of polarization that looks like B-modes, rather than just the usual E-modes. If we can detect the B-modes from this source, we'll get a very useful probe of the physics of inflation (or else evidence that the simplest models of inflation can't be right and we'll need to try harder).

The problems here are that we've only been able to detect the E-mode of polarization in the past ~5 years or so; the lensing B-modes are 100 times weaker than that; and the B-modes from inflation are ten times weaker still. We therefore need great increases in the sensitivity of CMB experiments to be able to detect the signal from inflation. The people building these experiments think they can achieve this within the next decade -- CMB technologies have been getting better at a tremendous pace over the last 10-15 years, and it is expected that will continue.
posted by janewman at 8:25 AM on September 17, 2013 [7 favorites]


How could anything occur without some universe (for the most general value of the term) for it to occur in? It seems to me you have to have turtles all the way down in some form, or you've got nothing. Literally. And you're stuck with it forever unless what you had before wasn't really nothing.

It's really just language of the kind "when the Universe started..." that bugs me a little. The stuff of the big bang (that is, whatever combination of forces, particles, etc. interacted to cause it) already had to exist in some form for that event to have occurred, so why characterize it as the "start" rather than just "an earlier point in the Universe's history when a dramatic event happened that shaped the laws of physics as we know them"? Maybe it was just one of many phase transition events the same old universe has gone through over and over (as in Big Bounce theory variations)... Laymen do not interpret or read the word "universe" the same way as specialists. For most people, if it's possible to say something exists--and we know something must have existed prior to the BB--then the universe has already "started."
posted by saulgoodman at 11:11 AM on September 17, 2013


Physicsmatt, flagged as fantastic, as usual. One teeny quibble:
I'm still not convinced I'm not a Boltzmann Brain dreaming the rest of you.
In reality, of course, we are all dreams of the Red Queen.

More seriously,
We're at least able to ask pointed and coherent questions now, something that we've only recently been able to do in a manner that at least reasonably resembles physics. Much of this can't yet be tested, but some of it can, and maybe we'll be a bit more clever in the future [...]

Exactly so. Cosmology is finally getting its observational, empirical foundations filled in, and the precision of some of the measurements (Planck, for example) is truly astonishing. Radio observations are closing in on the Epoch of Reionization, when the first stars in the Universe ("Population III" stars, of course, because astronomers are forever doing things backwards) ionized the neutral hydrogen produced in physicsmatt's paragraph 6 above.

Here's a very nice large image showing what's going on: we're looking back over 12 billion years in time and making precision measurements of the birth of galaxies and the emergence of large scale structure in the Universe. We can (or soon will be able to) see this happen!

(But what a competitive mess, with LOFAR, MWA, PAPER, LWA, all chasing after the same science.)
posted by RedOrGreen at 11:15 AM on September 17, 2013 [2 favorites]


Kid Charlemagne: "Biotech. Go for an unstoppable army of mutant geckoes or mind-control plague, or a neural interface for a supercomputer, ensuring you, and not some machine without the biochemical ability to gloat over vanquished enemies or lust after conquest, are the beneficiary of singularity.

Score!!! Uh, I mean, how 'bout them red birds!
"

Look. I got dibs here. I called world domination first.
posted by Samizdata at 11:56 AM on September 17, 2013


physicsmatt: "As a final note, how did we all miss that the physicsmatt signal is clearly The MattSignal? I also demand Mattarangs."

Too many Matts...I will brook no pretenders. And also, thanks for your usual excellent info.
posted by jquinby at 12:09 PM on September 17, 2013


Metafilter is truly a wonderful place! I'm so glad a random vacuum fluctuation/collapse of a 4D star/ unknowable first principle made this discussion possible.

Thank you janewman, physicsmatt and everybody! Reading this thread made procrastination feel like real education today.
posted by Kevin Street at 1:40 PM on September 17, 2013


I just caught that episode of ST:TNG where Wesley accidentally traps his mom in a pocket universe. Now it seems so realistic.
posted by XMLicious at 8:05 PM on September 17, 2013 [1 favorite]


Btw, here is the simplest possible way of explaining 'extra dimensions'.

If you want to tell something exactly where something happened on the surface of the earth, you can specify latitude, longitude, height and the time, for example. Let's call latitude x1, longitude x2 and time t.

But wait, what if you're in a multi-story building or an airplane? You need another dimension, height, and call it x3. Now you've got a 3-dimensions of space, and one of time, a 3+1 universe.

So just imagine you need one more number to specify a location, and call it X4. It doesn't matter where it is or where it goes, it's just more space for stuff to happen.

Just like you can use calculus to predict the motion of a projectile in 2-d space or 3d-space, you can equally as well predict it in 4d or 5d or however many dimensions you like and the physics all works out basically the same. You just can't visualize it.
posted by empath at 10:23 PM on September 19, 2013


« Older It's not too often that we come across photos that...   |   It's like Shark Week, but for goats Newer »


This thread has been archived and is closed to new comments