Composition of the Universe

February 11, 2009 11:19 AM

A fascinating talk about the composition of the universe [Youtube, approx 1 hour], presented by Sean Carroll, theoretical physicist at CIT. [via]

His talk is fast-paced and high level, but has enough detail to get the imagination fired up. Topics include ordinary matter, the standard model, dark matter, dark energy, string theory, supersymmetry, and the expanding universe. The presentation is extremely coherent and easy to follow, even for non-theoretical-physicists such as myself. Enjoy.

posted by knave (27 comments total)

neat. fyi, Carroll is a frequent contributor to the group blog Cosmic Variance, which has a pleasant (to me) mix of science-y and non-science-y posts.
posted by chalkbored at 11:53 AM on February 11, 2009

Sean Carroll is a really good teacher. He taught my undergrad general relativity class at Chicago, and presented the material with a good balance of rigor and clarity.
posted by mai at 12:07 PM on February 11, 2009

SPOILER ALERT

It's turtles all the way down.
posted by mullingitover at 12:07 PM on February 11, 2009 [3 favorites]

Physicists don't understand 95% of the universe. I don't understand 95% of what physicists understand. It's a wonder that I manage to feed and clothe myself.

That said, I love this stuff! I really hope I'm able to upload my brain into a computer before I die so "I'll" be around when they figure it all out.
posted by diogenes at 12:27 PM on February 11, 2009

How does one determine the percentage you don't understand of something you don't understand?
posted by weapons-grade pandemonium at 12:38 PM on February 11, 2009

Best of the web.

If ever figure out Dark Matter, future generations will find it hilarious that we referred to it by such a frankly ignorant name. It would be as if pre-Watson/Crick/Franklin biologists referred to DNA as "Gene Carrying Thingy".
posted by Joe Beese at 12:39 PM on February 11, 2009 [2 favorites]

How does one determine the percentage you don't understand of something you don't understand?

It's a rough estimate.
posted by diogenes at 12:42 PM on February 11, 2009

Does this have something to do with the new Pepsi logo?
posted by adamrice at 12:43 PM on February 11, 2009 [3 favorites]

This is good. Here goes my next hour and a quarter. Thanks, knave.
I don't use the smiley enough, diogenes ;^)
posted by weapons-grade pandemonium at 12:50 PM on February 11, 2009

Wow, thank you so much for that . . .

I want more . . . particularly an inroad into just how string theory is so potentially useful at explaining things . . .

Where would one (an ignorant but fascinated arts student) go from here to find similarly accessibly presented but more in depth readings or writings or talkings in the field? Any recs?
posted by protorp at 12:55 PM on February 11, 2009

How does one determine the percentage you don't understand of something you don't understand?

One of the members of the previous presidential administration diagramed this fairly well. First, make the simplifying assumption that unknown unknowns = 0. Second, divide known knowns by the quantity (known knowns + known unknowns) and subtract the ratio from 1. Note that unknown knowns is not in the expression, so that even if unknown knowns > 0 you get the same answer. Therefore this method is robust to forgetfulness, which is a very remarkable and useful property for a knowledge-assessment method.
posted by Llama-Lime at 1:16 PM on February 11, 2009 [1 favorite]

Then you have the Higgs boson...the only problem is we haven't found it yet...It could be that it's not there; it could be that this idea that we have of the Higgs boson needs to be replaced by a better idea. We don't have that better idea yet.

I love this. Can you imagine what would happen if the Pope were to say, "Then we have God and the Devil. The only problem is we haven't found them yet. It could be that they're not there; it could be that this idea we have of God and the Devil needs to be replaced by a better idea. We don't have that better idea yet.
posted by weapons-grade pandemonium at 1:21 PM on February 11, 2009 [1 favorite]

Eh, "dark matter" isn't such an embarrassing name, once you realize where it comes from, that is, "anything that isn't emitting light, you know, stars." Telescopes, and the light we receive from stars, have long been the source of just about everything we can determine about the cosmos.

It's a pretty solid name for something that could cover anything from brown dwarfs, interstellar hydrogen, WIMPs, etc. We could use "indirectly-inferred gravitational effect generating stuff," but IIGEGS sounds kinda funky.
posted by adipocere at 1:40 PM on February 11, 2009 [1 favorite]

You're being a bit too literal with your interpretation, adipocere. Most of dark matter is non-baryonic.

The total amount of baryonic dark matter can be calculated from big bang nucleosynthesis, and observations of the cosmic microwave background. Both indicate that the amount of baryonic dark matter is much smaller than the total amount of dark matter.
posted by weapons-grade pandemonium at 1:49 PM on February 11, 2009

See the explanation 25 min. into the video.
posted by weapons-grade pandemonium at 1:58 PM on February 11, 2009

No, I'm not being too literal with my interpretation. The name came about because we could not observe it through emitted radiation, we could only infer it. Baryonic or not, that had nothing to do with the choice of name.

Now, you seem to be laboring under the idea that I believe dark matter to be baryonic. I do not. WIMPs are non-baryonic, and were included in my list. And there's an etc in there, which can cover fun stuff like neutralinos (to be fair, I'm not sure anyone has decided to assign baryon numbers or baryon-like numbers to the posited supersymmetric partners of ordinary matter). I'm pretty aware that we have ruled out most of the forms of "normal" matter, but it's nice to start with stuff we know exists, rather than the zoo of "well, we haven't directly observed this stuff yet, but here's some ridiculous thing we'll postulate," like, say, axions.
posted by adipocere at 2:19 PM on February 11, 2009

adipocere: brown dwarfs, interstellar hydrogen, WIMPs, etc

Now, you seem to be laboring under the idea that I believe dark matter to be baryonic

I wouldn't know why. You get 50% for the WIMPS and the etc, though.
posted by psyche7 at 3:05 PM on February 11, 2009

Hey guys! This talk was pretty cute. Some background: I'm typing this (well, typing is the wrong word. I'm thinking this very loudly) from the iAmaZunehoo Metastore in 2668.

I bought a Temporal Package Tour with an English fellow from 1889 and a Cretan from 2200 B.C. The English guy is kind of losing his shit, but the Cretan is taking it in stride. Odd. Anyway, we've just finished reading THE BASIC STRUCTURE OF SUPERSPACE by Tanitha Lopez, published 2665. Softcover. It turns out Dark Matter and Dark Energy are mutli-universe functions vibrating the sHiggs-Field within and without an ever expanding and limitless amount of space-time (working background, of course, from a non-material quantum probability state. These "objects" move between time to cross super-dimensional space, but are rarely stable) and the expansion and contraction of these dimensions are curled into a slight "V" shape which gives mass to stronger forces of the proto-Lopez matrix, creating areas of deceleration within acceleration zones, pulling and compressing the Gluton and sGraviton wave/partical relationship, comparative to the observer, of course.

What it means is that it's tortoises, all the way down. Not turtles. Also Sea Slugs are now the dominate species.
posted by The Whelk at 3:34 PM on February 11, 2009 [1 favorite]

I am excited to see this debate pan out. Its clear to me that we will have to abandon the standard model completely soon. Dark matter and the higgs boson are both great examples of how existing models avoid specifically explaining some very fundamental stuff.

The nature of reality seems to be a "what if?" scenario whereas scientists seem to think it is a "this is therefore that is blah blah" with rigid rules and expected outcomes.

As participants in a what-if experiment we may never be able to fully understand how the box we're in is constructed. When we do try to see what the stuff inside the box is made up of we find "points in space (volume-less!) that are endowed with properties of mass, charge and spin." So really it appears we are just holograms, projections of energy trapped in the falsely titled "particles."

Interestingly, this is exactly what a computer simulation of reality might look like to a conscious observer within the simulation. The program would have information like "There is a point here with these properties." Say your little observer is programmed to be curious - if he digs in to see what that point is "made of" he repeatedly comes up blank or with confusing results. Thats because his reality is programmed to look real by using constructs like particles but does not actually include the particles. So they can't be studied. Its just not in the code. You are stuck studying outcomes forever, with no possibility of learning anything beyond what reality is programmed to offer it's observer as "hard evidence".

I think the consciousness that exists outside the boundaries of our reality had occasion to ask "what if?" and our universe is one of the many results of that question. But given our limited perspective (we are stuck in here!), to fully articulate with human terminology the source, exact inner workings, or ultimate destination of the universe will always be to some extent futile.
posted by cbecker333 at 3:42 PM on February 11, 2009

I think the consciousness that exists outside the boundaries of our reality had occasion to ask "what if?" and our universe is one of the many results of that question. But given our limited perspective (we are stuck in here!), to fully articulate with human terminology the source, exact inner workings, or ultimate destination of the universe will always be to some extent futile.

Interesting idea cbecker. I'm an atheist, but the closest I ever come to believing that there was a creator is when I deep dive into this stuff. It really feels like we're looking deeper into the inner workings than anybody bothered to "program." I'm hoping that will change as we learn more. The idea that we can never fully understand the universe is depressing.
posted by diogenes at 4:18 PM on February 11, 2009

Physicistance is futile.
posted by jamstigator at 4:34 PM on February 11, 2009

As participants in a what-if experiment we may never be able to fully understand how the box we're in is constructed. When we do try to see what the stuff inside the box is made up of we find "points in space (volume-less!) that are endowed with properties of mass, charge and spin." So really it appears we are just holograms, projections of energy trapped in the falsely titled "particles."

I detect an infinite regress here.
posted by Mental Wimp at 5:37 PM on February 11, 2009

"If ever figure out Dark Matter, future generations will find it hilarious that we referred to it by such a frankly ignorant name. It would be as if pre-Watson/Crick/Franklin biologists referred to DNA as "Gene Carrying Thingy".


Ever hear of Caloric or the Phlogiston theory?
posted by UseyurBrain at 6:04 PM on February 11, 2009

The first 48 seconds of this video:

...the things we've learned about the universe over the past 10 or 20 years which, coincides with my career as a working physicist, but I don't think I had much to do with it. In fact, none of us theorists have had much to do with it...observers and experimentalists have learned what the universe is made of...

Dark matter is stuff no one understands::A priest raises a wafer of unleavened wheat dough and it becomes the body of the Christ.

I am an observer and an experimentalist. You are a theorist. Therefore,...

...what???
posted by sluglicker at 8:43 PM on February 11, 2009

Great talk. In particular the explanations of how the ideas of dark matter and dark energy have come about from the earlier part of the talk.

But in the later part of the talk there were moments of interest too. The idea of experiments to look at how small a scale inverse square gravity works on..

And in the Q&A, the question about expansion of the universe and expansion of objects. If his argument about objects that are held together not growing, but the space between growing is to make any sense, there must be a middle ground of material that is separate more slowly than the rate of growth of the universe, but not stuck together completely either (like.. is the space between galaxies in a cluster growing with the expanding universe? What about stars in a single galaxy?). Also interesting on that scale.. I wonder how much gravitational potential energy is being stored in the separation of all this matter. Surely not much on the scale of dark energy, but it would be a neat number to hear about..
posted by Chuckles at 8:48 PM on February 11, 2009

So, the universe is not only stranger than we think it is, it's stranger than we can think it is. What a novel, intriguing idea. Let me think about it.
posted by sluglicker at 9:09 PM on February 11, 2009

adipocere has it right, AFAIK: The term "dark matter" has been around for longer than we've known that most of the dark matter must be interestingly non-baryonic, and has covered all the various theories for what it might be, including the pedestrian ones like brown-dwarf MACHOs. It really did originate as "stuff that isn't emitting light" or "stuff we can't seem to observe directly" (a very slightly metaphorical meaning of "dark").
posted by hattifattener at 1:23 AM on February 12, 2009