cosmic inflation
November 4, 2021 10:10 PM   Subscribe

We now know the big bang theory is (probably) not how the universe began - "The Big Bang still happened a very long time ago, but it wasn't the beginning we once supposed it to be."
Extrapolating back to as far as your evidence can take you is a tremendous success for science. The physics that took place during the earliest stages of the hot Big Bang imprinted itself onto the universe, enabling us to test our models, theories, and understanding of the universe from that time. The earliest observable imprint, in fact, is the cosmic neutrino background, whose effects show up in both the cosmic microwave background (the Big Bang’s leftover radiation) and the universe’s large-scale structure. This neutrino background comes to us, remarkably, from just ~1 second into the hot Big Bang.

But extrapolating beyond the limits of your measurable evidence is a dangerous, albeit tempting, game to play. After all, if we can trace the hot Big Bang back some 13.8 billion years, all the way to when the universe was less than 1 second old, what’s the harm in going all the way back just one additional second: to the singularity predicted to exist when the universe was 0 seconds old?

The answer, surprisingly, is that there’s a tremendous amount of harm. The reason this is problematic is because beginning at a singularity — at arbitrarily high temperatures, arbitrarily high densities, and arbitrarily small volumes — will have consequences for our universe that aren’t necessarily supported by observations.
also btw...
posted by kliuless (44 comments total) 56 users marked this as a favorite
 
Is the Great Neutrino Puzzle Pointing to Multiple Missing Particles? - "Years of conflicting neutrino measurements have led physicists to propose a 'dark sector' of invisible particles — one that could simultaneously explain dark matter, the puzzling expansion of the universe, and other mysteries."
A rich, complex dark sector could offer a solution to why the present-day universe seems to be expanding faster than expected — a phenomenon known as the Hubble tension — and why galaxies don’t seem to cluster as much as they should if dark matter is a single, inert particle. “Changing the physics of dark matter here would really have an impact on this type of cosmological tension,” said Christina Kreisch, an astrophysicist at Princeton University.

The models resonate with older ideas. For instance, the existence of very heavy neutrinos was first hypothesized decades ago to explain the puzzlingly small masses of the three known neutrinos. (In a “seesaw mechanism,” the masses of the known, lightweight neutrinos and heavy ones could have an inverse relationship.) And the decay of heavy neutrinos moments after the Big Bang has been suggested as the possible reason why there’s so much more matter than antimatter in the universe. “Many people, including myself, are working on exploring such connections,” said Kopp.
posted by kliuless at 11:42 PM on November 4, 2021 [5 favorites]


This whole field is like standing on the edge of a huge lake and seeing the tiniest rippl and calculating the size of the pebble dripped in the center by a seagull. What we probably can't really know is if it was a seagull or an old guy with a long beard and amazing throwing arm.
posted by sammyo at 4:37 AM on November 5, 2021 [9 favorites]


If the Big Bang began from a singularity, we have no explanation; we simply have to assert “the universe was born this way,” or, as physicists ignorant of Lady Gaga call it, “initial conditions.”
posted by Obscure Reference at 4:38 AM on November 5, 2021 [9 favorites]


This is super fascinating, but isn't the inflationary universe also "no explanation" in the same way as the Big Bang? Because the inflation would have erased any information about what came before, we have no idea at all why it occurred either. Am I missing something?
posted by contrapositive at 5:07 AM on November 5, 2021 [2 favorites]


Am I missing something?

We all are, and these folks are all doing their damndest to figure it out. They may be going down the wrong path, or on a fool’s errand entirely even for trying, but I applaud the effort.

For entirely irrational reasons, I am on Team Axion when it comes to dark matter. But even if axions get ruled out, I will cheer the science on from the sidelines no matter which team wins.
posted by notoriety public at 5:33 AM on November 5, 2021 [4 favorites]


Inflation accomplishes this by postulating a period, prior to the hot Big Bang, where the universe was dominated by a large cosmological constant (or something that behaves similarly): the same solution found by de Sitter way back in 1917.

And earlier in the article...

In 1917, Willem de Sitter found the solution for an empty universe with a cosmological constant, which describes an exponentially expanding universe. (emphasis added)

So could this mean, for instance, that our current expanding universe might continue to do so, ever lessening in density, until it is practically empty, thus matching the de Sitter model and providing the initial conditions for a new big bang without ever contracting?
posted by solotoro at 5:48 AM on November 5, 2021 [1 favorite]


I don't know how to evaluate the validity of this site's source but their mission statement is a bit vague for me to trust science coming from it.
posted by tiny frying pan at 6:15 AM on November 5, 2021 [5 favorites]


In 1917, Willem de Sitter found the solution for an empty universe with a cosmological constant, which describes an exponentially expanding universe.

Not on topic I suppose but this statement reminded me of working in restaurants when guests wouldn't write in a specific tip amount to their checks, instead just writing a total amount they wanted to pay on the bottom line and the word 'math' where the tip should be.

de Sitter's constant sounds a lot like 'math' to me. ;->
posted by Insert Clever Name Here at 6:53 AM on November 5, 2021 [11 favorites]


It's good to see The Big Bang Theory being questioned. Like Terence McKenna used to say about the theory: “Modern science is based on the principle ‘Give us one free miracle and we’ll explain the rest.’ The ‘one free miracle’ is the appearance of all the mass and energy in the universe and all the laws that govern it in a single instant from nothing.”
posted by Liquidwolf at 7:02 AM on November 5, 2021 [13 favorites]


^ then again, 'miracle' is just fewer syllables than "hold your horses, we're getting to that"
posted by elkevelvet at 7:18 AM on November 5, 2021 [6 favorites]


"In the beginning there was nothing, which exploded."

Terry Pratchett
posted by Archer25 at 7:22 AM on November 5, 2021 [42 favorites]


OK, I'll do it - Metafilter: I don't know how to evaluate the validity of this site's source but their mission statement is a bit vague for me to trust science coming from it.
posted by achrise at 7:22 AM on November 5, 2021 [22 favorites]


I would never say that about Metafilter. I find our userbase is meticulous about inspecting sources.
posted by tiny frying pan at 7:23 AM on November 5, 2021 [5 favorites]


loose paraphrase of a comment by Felix Pirani: "The Big Bang Theory is what we have today, and will probably be replaced by something else in the future."
posted by ovvl at 7:56 AM on November 5, 2021 [1 favorite]


"The Big Bang Theory is what we have today, and will probably be replaced by something else in the future."

There is another theory which states that this has already happened.
posted by notoriety public at 8:23 AM on November 5, 2021 [28 favorites]


I don't know anything about the site, tiny frying pan, but as someone who's taught a few classes titled "the big bang," the article doesn't seem obviously wrong or crackpot to me. It's worth noting that they're using the phrase "big bang," is a very specific way that even most cosmologists who aren't early universe theorists are often much more casual about. (If by big bang, you mean that the observable universe was very much smaller and hotter and it's been expanding according to something pretty close to general relativity and known physics with a few surprising additional constants for 14 billion years. . . everything in the article could be called a big bang model.) The implications of inflation are interesting and fun to think about. But, it doesn't really change our understanding of things that have been measured.

I also worry a little about how the word "crisis" reads to most people. It's definitely the word working cosmologists use, but it means something much closer to, "wow, this might be new physics. Neat! Let's explore it," rather than a bad thing, at least for most. One could instead call it the H_0 triumph: that multiple groups working with very different techniques have convinced each other their astonishingly precise measurements might both be right is pretty cool. Not every generation gets to see a paradigm shift. (If forced to bet, I'd probably bet against new physics. But, I sure hope I'm wrong, and it seems more likely as time goes on.) The latter articles also seem legit, with some really petty caveats about the definition of "one equation."

(Looking into the author a bit, Ethan Siegel's wikipedia page sure is detailed in a way that is unusual. I'm not sure that's actually a bad thing. His old papers look entirely reasonable.)
posted by eotvos at 8:25 AM on November 5, 2021 [11 favorites]


Despite the "we now know" headline, I can't tell from the article whether this is describing a shift in the consensus, or this is simply an interpretation that's been around a while that the author happens to like.
posted by mark k at 8:28 AM on November 5, 2021 [3 favorites]


They say it all started out with a big bang. But, what I wonder is, was it a big bang or did it just seem big because there wasn't anything else drown it out at the time?

--Karl Pilkington
posted by NoThisIsPatrick at 8:47 AM on November 5, 2021 [10 favorites]


"What is it that breathes fire into the equations and makes a universe for them to describe? Why does the universe go to all the bother of existing?" - Stephen Hawking in A Brief History of Time
posted by neuron at 8:54 AM on November 5, 2021 [7 favorites]


This was a weird article, kept expecting them to explain something new or a new discovery or theory or idk... Felt like this was just explaining the big bang. Everything described in here is what I know of as the big bang and I thought one of the main points of big bang was that nobody can know what exactly was going on before a certain point. This whole article just seems to be re-treading that and calling it something else to make a distinction I'm not sure needs to be made.
posted by GoblinHoney at 8:54 AM on November 5, 2021


The title of the first link is misleading. It implies that we’ve somehow decided that the Big Bang theory is incorrect. Instead, the article just seems to say that yes, the big bang happened but we can’t really extrapolate back into the very first second. Which I didn’t think was news. I wish he had done a better job of explaining how “inflationary theory” is somehow different from the idea of a singularity. I don’t quite get it. But a lot of great stuff in there and the other links.
posted by freecellwizard at 8:59 AM on November 5, 2021 [5 favorites]


May I recommend The End of Everything by Katie Mack for the most understandable treatment of all the possible ways the universe could end, plus some clarity about the beginning.
posted by Peach at 9:33 AM on November 5, 2021 [2 favorites]


I'm also an astronomy prof, I've worked a bit with Ethan, he contracted me to write a popular article on similar topics, although this is not my specialty. He does a lot of science popularization and is very solid. He has a textbook out. Not primarily a researcher.

And yes, I think the gist of this is that it's another way to look at things, what most people mean by the Big Bang is the universe has been expanding, we can trace that back billions of years to the Cosmic Microwave Background, to primordial nucleosynthesis that left us with the fractions of elements we have in the oldest stars, etc. We all know as we extrapolate further backwards our models get fuzzier. If you think of the Big Bang as The Beginning, this is an intuition pump that our science hasn't gotten to The Beginning yet.

Inflation solves some problems but it's also very adjustable. Something has to turn it off at just the right time. Avi Loeb, former chair of the Harvard astronomy department and now rather infamous for hyping that this interstellar comet could have been an alien spacecraft, along with some other scientists wrote a controversial claim to Scientific American that the Inflationary add-on to the Big Bang was now not even scientific, because it was too adjustable. Ethan has a much more positive take on inflation and its partial confirmation through ripples in the cosmic microwave background.

I don't think anybody expects a literal singularity. We simply can't extrapolate to that situation without a quantum theory of gravity.

There are a lot of ideas out there at the frontier, some more speculative than others (Penrose's cyclic cosmology).
posted by Schmucko at 9:58 AM on November 5, 2021 [21 favorites]


I don't know how to evaluate the validity of this site's source but their mission statement is a bit vague for me to trust science coming from it.

Cite ?
posted by They sucked his brains out! at 10:14 AM on November 5, 2021


"The Big Bang Theory is what we have today, and will probably be replaced by something else in the future."

It turns out that the "something else" is Young Sheldon.
posted by Strange Interlude at 10:21 AM on November 5, 2021 [4 favorites]


Came for Penrose, left satisfied.
posted by zengargoyle at 10:49 AM on November 5, 2021 [1 favorite]


This is why I've turned my attention towards creating a smaller, less complicated and more understandable pocket universe to move into. This one is a fucking mess and the sooner we admit this and make our escape plan the better.
posted by interogative mood at 11:13 AM on November 5, 2021 [8 favorites]


I'm waiting for physicists to announce that the universe is bigger on the inside than it is on the outside.
posted by SPrintF at 11:45 AM on November 5, 2021 [3 favorites]


I don't know how to evaluate the validity of this site's source but their mission statement is a bit vague for me to trust science coming from it.

Cite ?

It is on their website in an "about us" section, much like many websites.
posted by tiny frying pan at 12:18 PM on November 5, 2021


And to extend my flip pebble comment, we are doing all these observations with sunglasses and a veil. Go Webb telescope at L2! It will be using the earth as a sun shield and peeping at wavelengths that are muddied by air. So expect a whole passel of theories to be revised in the next few years.

And I can't go deeper but :

2020 — Scientists publish a study which suggests that the Universe is no longer expanding at the same rate in all directions and that therefore the widely accepted isotropy hypothesis might be wrong.

I liked a theory that I can't track down just now where the universe is sort of a 4+ dimensional torus (donut) shape that curves around on itself. A legit theory that I guess worked for a bit but the data keeps returning to the big bang.
posted by sammyo at 12:45 PM on November 5, 2021 [2 favorites]


I’m surprised Alan Guth’s seminal “The Inflationary Universe” isn’t mentioned in the main article or the accompanying piece.
posted by syzygy at 12:57 PM on November 5, 2021


This is why I've turned my attention towards creating a smaller, less complicated and more understandable pocket universe to move into.

Pfft. The pocket universe I'm building is bigger, more complicated, and less understandable than this one. But it's got blackjack. And hookers.
posted by GCU Sweet and Full of Grace at 2:00 PM on November 5, 2021 [4 favorites]


could this mean, for instance, that our current expanding universe might continue to do so, ever lessening in density, until it is practically empty, […] providing the initial conditions for a new big bang without ever contracting?
I first heard this suggestion about ten years ago, at a conference, from Guth himself. The gist of the proposal is that inflation is what the vacuum does most of the time. Our mostly-flat universe, where the acceleration is small, is a fluctuation.
posted by fantabulous timewaster at 2:05 PM on November 5, 2021 [1 favorite]


As I understand it, the matter/antimatter asymmetry works as follows:

1. Start with 0.
2. 0 = 1 + (-1)
3. ????
4. 1

We just have to clarify step three.
posted by dephlogisticated at 2:09 PM on November 5, 2021


Pfft. The pocket universe I'm building is bigger, more complicated, and less understandable than this one. But it's got blackjack. And hookers.

A fella could throw a hell of a party in an Infinite Fun Space like that.
posted by notoriety public at 2:20 PM on November 5, 2021 [2 favorites]


Nthing recommend on Dr. Katie Mack's book. She's also a good follow on Twitter.
posted by rikschell at 3:55 PM on November 5, 2021 [1 favorite]


As I understand it, the matter/antimatter asymmetry works as follows:

1. Start with 0.
2. 0 = 1 + (-1)
3. ????
4. 1

We just have to clarify step three.


Isn't step 4 more like 0.000000000000000000000000000000000000000000001 or whatever (but still nonzero) ? As far as I understand, most matter and antimatter annihilated each other, but for unknown reasons there was a teensy tiny amount of matter left over that is our current universe
posted by ymgve at 7:51 PM on November 5, 2021 [1 favorite]


calculating the size of the pebble dripped in the center by a seagull

I don’t think that was a pebble.
posted by romanb at 12:50 AM on November 6, 2021 [4 favorites]


This is an odd article, as it seems to just be saying "the way Carl Sagan explained it in Cosmos was right", no?
posted by rum-soaked space hobo at 2:20 AM on November 6, 2021


I'm waiting for physicists to announce that the universe is bigger on the inside than it is on the outside.
posted by SPrintF

Or that we are the antimatter universe.
posted by Pouteria at 4:52 AM on November 6, 2021


We're obviously the anti-matter universe because our electrons somehow have negative charge.
posted by straight at 10:52 AM on November 6, 2021 [3 favorites]


What's changed since Sagan's Cosmos?

We've turned cosmology into a precision science using the tool of the Cosmic Microwave Background, radiation filling all space from 380,000 years after the Big Bang. We've mapped out the expansion of the universe using supernova explosions. We've found the effect of dark matter (or a problem with our current theory of gravity, but probably dark matter) and dark energy. We've simulated how the galaxies developed from the ripples of 380,000 years after the Big Bang.

The Big Bang, at least as we used to think of it, is now really well matched by observations. There was a time when the Steady State theory could fall back on: ok, galaxies are moving apart but maybe new galaxies appear in the gaps. Maybe this "Cosmic Microwave Background radiation" is just dust heated up by star light. But details of the CMB only fit the Big Bang.

So the Big Bang is really solid, but that's made further back in time the new speculative frontier. And maybe Inflation is about where the Big Bang was around 1970-1990. Some good evidence for it, details not measured all that well, and some detractors. Basically that a LOT could have gone on in the merest fraction of a second, and instead of complete speculation, this is the new frontier.

The evidence for Inflation was weaker during Sagan's Cosmos, and there was the basic Big Bang to shore up more. Now we have to deal with the horizon problem and the flatness problem, why is the universe so equal in all directions and why does the matter and energy add up to cause space on average not to be curved.
posted by Schmucko at 12:03 PM on November 6, 2021 [8 favorites]


I don’t know what I like more.

A Culture GCU being a futurama fan and quoting Bender at humans.

Or futurama taking place in the Culture and Bender somehow ends up as a GCU called Sweet and Full of Grace.
posted by Dr. Curare at 6:31 PM on November 6, 2021


Laws of Logic Lead to New Restrictions on the Big Bang - "Physicists are translating commonsense principles into strict mathematical constraints on how our universe must have behaved at the beginning of time."
The unfathomable ocean that theorists aim to plumb is a brief but dramatic stretch of space and time that many cosmologists believe set the stage for all we see today. During this hypothetical era, known as inflation, the infant universe would have ballooned at a truly incomprehensible rate, inflated by an unknown entity akin to dark energy.

Cosmologists are dying to know exactly how inflation might have happened and what exotic fields might have driven it, but this era of cosmic history remains hidden. Astronomers can see only the output of inflation — the arrangement of matter hundreds of thousands of years after the Big Bang, as revealed by the cosmos’s earliest light. Their challenge is that countless inflationary theories match the final observable state. Cosmologists are like film buffs struggling to narrow down the possible plots of Thelma and Louise from its final frame: the Thunderbird hanging frozen in midair.

Cosmic bootstrappers strive to winnow the crowded field of inflationary theories with little more than logic. The general idea is to disqualify theories that fly in the face of common sense — as translated into stringent mathematical requirements. In this way, they “hoist themselves up by their bootstraps,” using math to evaluate theories that can’t be distinguished using current astronomical observations.
posted by kliuless at 1:11 AM on November 12, 2021


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