Concerted response to the most common cosmo confusions

[Martin]

RaulDuke started a valuable thread in which a number of persistent confusions came to light. He elicited excellent responses from several people---Airbrush, Sisyphus, NowThat, Severian and probably others I'm forgetting.

 

The thread has grown. I'd like it if we could have a shorter focused thread that examines the causes of the confusion that people (not just RaulDuke) get into.

 

The reaction was kind of coherent and unanimous, on most points, which is one reason I think it worked.

 

An exception that stands out in my mind is that early on Sisyphus made the key point, which then was seemingly forgotten as a ton of other comment, often informed and valuable, poured in. The key point he made is that

expansion of distances is not motion in space. In ordinary motion, there is some destination out there that you get closer to. That doesn't happen in cosmo expansion.

 

...I am under the impression that we are 13.7 billion ly from the origin of the universe. If we expanded under the speed of light, than we shouldnt be able to see that far back in time...

 

 

Indeed, it seems you are under the impression that the Big Bang and the expansion of space are like an explosion moving away from a central point. This is not the case. The universe has neither a center nor edges. Its origin is everywhere at once, and its expansion is not movement, but an increase in the amount of space itself. These are difficult and counterintuitive concepts, and it takes a while to get used to them...

 

When newcomers arrive with this misconception, we all need to hammer it into them that expansion is not motion. Don't let them slip back into the old habit of talking about expansion as if it were a kind of motion.

 

Also there are two other common misconceptions:

the explosion picture

singularity pictured as a single point.

 

The response was unanimous in this case and Raul got the message:

 

Thanks, I now see my flaw. I was under the impression that all things were created at a central point...

 

I believe I understand what is going on now. Every documentary, everything that I have read makes it seem that a singular point started it all, but that is what was confusing me as it didnt make sense with our current universe...

 

Singular does not mean single. The root meaning of the technical term is "odd or peculiar". On my way here I saw a singular man acting in a singular fashion---this means I saw a weird man acting weirdly. It doesn't mean I saw a bachelor--a single man--who was concentrating on doing one single action.

 

In mathematics a singularity is a situation or region where some manmade theory breaks down/blows up. It doesn't have to be a single isolated point. A singularity can be a large region, or a place where a function fails to be defined. Acts weird. Produces meaningless infinities, etc. This might be at a single isolated point (and quite often is) but that's not what it means.

 

Things farther away are expanding faster than things closer to us, correct? ...

 

Here I would say Raul is slipping back into the habit of thinking of expansion as motion.

 

What can we do? It would be good if we had a coherent strategy. I'm open to hearing other ideas but I'll lay out what seems to me so far to work the best. You've heard it before: it's the Balloon Sermon.

 

Think of all existence, all space and matter, concentrated on the surface of the balloon. There is no outside or inside space, only the surface. And any creatures would be 2D amoebas slithering around.

 

White dots speckle the surface, they are galaxies.

 

Each dot stays at the same latitude and longitude, which is what we mean by not moving. That makes sense because if the balloon expands no dot gets closer to any other---in true motion there is always some place you get closer to.

 

Wigglers called photons move across the surface always at the same speed of one millimeter per second.

 

Google "wright balloon model" and watch and think about it some.

 

After 60 seconds a photon will clearly be farther than 60 millimeters from its point of origin, even though it travels at a constant speed, because the distance that it has already covered expands.

 

Likewise after 13.7 billion years a photon will be farther from its point of origin than a mere 13.7 billion lightyears.

 

I have to go, back later. Do other people have some ideas of how we can best handle this type of situation?

 

BTW thanks to everybody who put in a word on the other thread.

Edited May 7, 2009 by Martin

[NowThatWeKnow]

 

When newcomers arrive with this misconception, we all need to hammer it into them that expansion is not motion. Don't let them slip back into the old habit of talking about expansion as if it were a kind of motion.

 

Also there are two other common misconceptions:

the explosion picture

singularity pictured as a single point.

...

What can we do? It would be good if we had a coherent strategy. I'm open to hearing other ideas but I'll lay out what seems to me so far to work the best. You've heard it before: it's the Balloon Sermon.

 

I am fairly new here but have already noticed many new people asking similar questions and they rarely prepare themselves with the basics. I often point them to Einstein Online or the stickies on cosmology basics. I would hate to run good people of requiring a prerequisite but we can suggest certain reading.

 

The "Balloon Sermon" worked well for me for understanding expanding space/increasing distances rather then movement through space. It helped when I visualized the balloon itself as a (most likely non existent) ether or fabric of space holding the galaxies somewhat in place. When you get a good visual in your head it sticks. Instead of Wigglers called photons I kept seeing ants on the balloon. Not sure why.

 

One problem with singularity and the big bang is that google searches still come up with this concept since it was common mainstream not that long ago.

 

Next

[Martin]

Instead of Wigglers called photons I kept seeing ants on the balloon. Not sure why.

...

 

LOL

 

Next

 

I don't have a next right at the moment. But it is nice to have a response so I can start a fresh post and take a new tack, if I get a notion to. Also maybe someone else with respond.

 

For now everything seems peaceful and in order. Relatively speaking.

[Airbrush]

A few months ago I saw a wonderful short video clip, posted here somewhere by Martin, of a nobel winner explaining the structure of the universe to a design school. I think he said the very early universe, at about the Planck Time was smaller than a proton. Did he mean that only the visible universe would have been that small? Or do they no longer give a hint at the size of the singularity of the universe, very, very shortly after the Big Bang?

[Martin]

A few months ago I saw a wonderful short video clip, posted here somewhere by Martin, of a nobel winner explaining the structure of the universe to a design school. I think he said the very early universe, at about the Planck Time was smaller than a proton. Did he mean that only the visible universe would have been that small? Or do they no longer give a hint at the size of the singularity of the universe, very, very shortly after the Big Bang?

 

Wait, let's get the link for that. I think it was George Smoot talking to the TED club (technology entertainment design leaders and trendsters). Google "smoot TED".

 

Hot dog. First hit =

[NowThatWeKnow]

Hot dog. First hit =

 

Interesting but... It sounds like they are talking about singularity like it happened. Isn't that what we are trying to discourage. And it didn't explain the expanding universe, something else we are promoting. Why do I not see this contributing to the purpose of this thread?

[Airbrush]

George Smoot said that the entire visible universe was once "smaller than an atom". That sounds very singular to me. But that implies a finite universe of only what we can see. If the universe is infinite, then all bets are off about the size of the singularity at the beginning. Does that mean that an infinite universe can orginiated out of a region of indeterminable size, before Planck Time?

[Martin]

George Smoot said that the entire visible universe was once "smaller than an atom". That sounds very singular to me. But that implies a finite universe of only what we can see. If the universe is infinite, then all bets are off about the size of the singularity at the beginning. Does that mean that an infinite universe can orginiated out of a region of indeterminable size, before Planck Time?

 

It doesn't sound like a singularity to me. It's just what you get if you take the observable universe as we now see it---matter density 0.2 nanojoules per cubic meter, including dark matter---and see how big it would be if compressed to Planck density.

 

the difference between classical and non-singular cosmology is simply whether the model breaks down or not. You still extrapolate back and find extreme density, extreme temperature, basically same old conditions as in the classical case.

 

If there was an initial singularity, which I see no reason to suppose (given that we have models being studied which do not break down) and if the universe is infinite spatial volume then the singularity was infinite. I wouldn't say "all bets are off". It clearly could not have been contained in a finite volume.

 

I like Smoot's lecture a lot. As a popular public lecture for Los Angeles and Silicon Valley smart generalists, I think it is terrific. I don't recall him saying that the universe began with a singularity. Saying that there was, at one time, an inconceivably hot & dense state is something else.

 

The aim of today's quantum cosmo model builders is to get back there and not have the model blow up, for a change . Have the model continue. They've got several approaches. They are getting increasing peer attention, conference visibility. They're running the stuff on computer. And trying to find some fine detail predictions of what we can see that differ from the classical model. The hard part is their new models predict very close to the same stuff about the CMB and overall structure.

 

Interesting but... It sounds like they are talking about singularity like it happened. Isn't that what we are trying to discourage. And it didn't explain the expanding universe, something else we are promoting. Why do I not see this contributing to the purpose of this thread?

 

I'm sorry. Does Smoot actually say singularity? Maybe he did, so please let me know. If he just said very hot very dense, that's of course fine!

If he said observable universe concentrated in volume the size of an atom, an atomic nucleus, or a proton, that's fine.

But if he said that since the classic theory breaks down (has a singularity) and therefore nature herself breaks down. If he said that time evolution stops. Then that's disappointing.

I guess I could forgive him---since it is a glitzy elite popular lecture, not an academic talk. But I would feel let down.

 

I put a calculation of the size the observable would have at Planck density over in the "cosmo basics" sticky thread. Maybe it will come in handy.

Edited May 8, 2009 by Martin

[NowThatWeKnow]

I'm sorry. Does Smoot actually say singularity? Maybe he did, so please let me know. ...If he said observable universe concentrated in volume the size of an atom, an atomic nucleus, or a proton, that's fine...

I remember him saying

"observable universe concentrated in volume the size of an atom,"

To the layman that sounds like singularity.

Good video but not pushing the agenda of this thread.

[cameron marical]

If the universe isnt having its contents moved away from each other, does that mean that something externall is coming in to our space and creating up that extra space?

 

Whats blowing up our balloon?

[Martin]

If the universe isnt having its contents moved away from each other, does that mean that something externall is coming in to our space and creating up that extra space?

 

Whats blowing up our balloon?

 

Cameron, in the context of GR and cosmology, space is not a substance that needs to be created or that expands or that contracts. What expands is the network of distances. Distances can change in accordance with

the main Einstein equation. Spacetime curvature means that geometry is dynamic, you have no right to expect distances NOT to change. Since they can, they will. And the Einstein field equation says in what way.

 

To make the balloon model work for you, you have to ignore the inside and the outside, think of all existence concentrated on the 2D surface. No air. No rubber. Pure dynamic geometry.

 

I remember him saying

"observable universe concentrated in volume the size of an atom,"

To the layman that sounds like singularity.

Good video but not pushing the agenda of this thread.

 

Thanks for recalling the quote! I should always remember to include something like that. I think it's a great talk and we should urge people to watch it, and just work with the size comparison and cope with it.

 

The typical size of an atom is one angstrom unit which is 1/10 of a nanometer. That is way way bigger than a proton.

100,000 times bigger.

 

He is being very cautious. He is only going back to 10^-15 of Planck density. Do you follow? 100,000 cubed is one million billion.

He is saying at some point the size of the observable is about an angstrom and the density is one millionth of a billionth of Planck.

 

The Ashtekar group has been running quantum gravity computer models where they find the bounce consistently happens at about 40% of Planck.

 

Smoot is being respectably conservative and only talking about the universe back to a much lower density. He stays in the regime where classical GR has a good chance of applying. He goes nowhere near where the "singularity" befalls GR. As long as he keeps well clear of it he doesn't have to say anything about what might actually have happened instead of the celebrated Glitch.

 

I sound like a Smoot fan. Maybe I am. Though Ned Wright shows where Smoot should have given some other researchers more credit in his Nobel acceptance speech.

[cameron marical]

you have no right to expect distances NOT to change. Since they can, they will. And the Einstein field equation says in what way.

 

Just a question man...

 

The distance between the galaxies is increasing, could that mean that the curvature of space is decreasing?{if space is indeed curved}

[Martin]

Just a question man...

 

The distance between the galaxies is increasing, could that mean that the curvature of space is decreasing?{if space is indeed curved}

 

There is a connection. At least with the standard cosmo model, which gives a pretty good fit to our universe, the two things are related. At least the overall average spatial curvature.

 

If you think of the simple toy picture, the balloon, you can see as distances increase the surface becomes less curved. The overall average curvature, not counting black holes and stuff, which the toy picture doesn't capture.

 

I don't want to think about how general that is---is it a general rule or not. I think it's probably not a general rule. I can imagine universes where the distance between galaxies is increasing but at the same time space is getting more pimply. So I don't want to say that what you are talking about would happen every time.

[Airbrush]

I remember him saying

"observable universe concentrated in volume the size of an atom,"

To the layman that sounds like singularity.

Good video but not pushing the agenda of this thread.

 

I watched the video to hear what he said about how small the observable universe could have been early on, and I think he did say smaller than an atom, but I don't remember him ever using the word singularity, just as Martin said.

 

It is hard to imagine 100 Billion galaxies compressed into an area smaller than an atom. That is beyond surreal!

 

So is the word singularity only used for black holes?

[Martin]

I watched the video to hear what he said about how small the observable universe could have been early on, and I think he did say smaller than an atom, but I don't remember him ever using the word singularity, just as Martin said.

 

It is hard to imagine 100 Billion galaxies compressed into an area smaller than an atom. That is beyond surreal!

 

So is the word singularity only used for black holes?

 

Yes it is beyond surreal :eek:

 

About using which words? I am generally comfortable with the way they talk at Einstein Online. You remember "A Tale of Two Big Bangs". The tendency to use The Singularity as a time-mark without assuming that the classical model (which blows up there) is adequate or even applicable. Use it as a reference point without assuming that

time started there

there was infinite density and infinite curvature (physically meaningless)

or that the classic model is tracking nature at that point.

 

And all the models made so far could be wrong, including the various bounce ones. What I see is intelligent people doing the best they can, trying to cope, quantizing the classic cosmological model, taking hints from partially successful quantum gravity attempts. Trying get the simplest quantum theory they can that is faithful to GR. (Or other worthy goals, like unification of gravity with a theory of matter.) I have a lot of respect for this effort, and I try to reflect and follow what seems to be the main currents.

 

I don't feel able to second-guess the future course of research. I'd certainly be happy if it turned out, with some revised theory, that the density needed for the bounce to happen was not as high as 40 percent Planck. Incredibly unimaginably high. Have to go back tomorrow.

 

Personally I'm happy whatever words the people I know decide to use because I know that there is a certain level of sophistication in how they think. No words are perfect.

 

Sophisticated cusses, they use the term singularity freely without believing that there is necessarily one in nature.

 

One simply doesn't know as yet. There is no scientific reason to suppose time stops, but there is also no good reason to suppose that time-evolution does not stop.

Edited May 9, 2009 by Martin

[Airbrush]

From the little I read about Superstring theory in Astronomy magazine, correct me if I am wrong, I think they said something like the Big Bang was the result of a collision of higher dimensions. I think it was like a couple of bed sheets handing on parallel laundry lines to dry in the sunshine. These flat sheets have only two dimensions of infinite size, and they represent two parallel higher dimensions that are very close together but not touching. The Big Bang was when they came together which might not be at a single point, but could have started from a region, or series of regions, of any size, then spreading outward in all directions? That would explain cosmic inflation?

[teranko]

Why does everyone assume the "Big Bang" was a singular event? It's my guess that the Big Bang is ongoing with matter constantly pouring in from the other membrane or whatever source of matter and energy you choose to accept. Given our space-time "volume" is porportional to the density of matter in it, it continues to expand. If the rate of expansion of the universe is accelerating, so is the rate that matter is pouring into it from the epi-center where the "big bang" occurred.

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Merged post follows:

Consecutive posts merged

Oh yeah, I should probably mention my other theory that black holes are not atom sized objects of unimaginable density but rather a porthole from our familiar 4D space time dimension into another dimension predicted by String theory. Imagine a point in our universe where space-time is pulled through a knot-hole and is turned inside out. The sack that forms fills up with the matter that is pulled into it beyond the event horizon and expands into the other dimension. Density differences between the various dimensions may determine the rate of accretion. Because this dimension occupies the same space that we do, it can't be seen, only "felt". The one thing I'm not sure about is "does the matter in the new dimension fill the other dimension(s) in the immediate area of the black hole or are there other laws of physics that permit the matter to scatter throughout the universe to maintain equilibrium?".

[Airbrush]

If black holes are like a connection with a higher dimension, then maybe that explains supermassive black holes. They exist in our universe because they originated in a parallel higher dimension and leaks over into our universe.

[jackson33]

The Universe has 3 spatial dimensions, but it is easier to visualize an analogy to its expansion for the 2-dimensional surface of a balloon. There is no center. If you stand on any galaxy, all the others will appear to be moving away from you with a velocity proportional to the distance from you. An analogy in 2 dimensions is to put dots on the surface of a balloon and blow the balloon up. As it expands, there is no dot that is the "center", but if you stand on any dot you will see all other dots moving away from you (and the rate at which they move away will be proportional to the distance. Dots close to you will be moving away slower than those further away). The expansion of the Universe appears to be like this, but in 3 rather than 2 space dimensions, which makes it much harder to visualize, but it is possible to describe it mathematically.

http://csep10.phys.utk.edu/astr162/lect/cosmology/expansion.html

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Martin;

Another explanation of 2D vs. 3D visualization of the U, which I simply can't or won't accept. Even in 2D, dots at the top of a balloon expand less that those centered half way down (while blowing up), but the U is at least a 3D (4 with time) object and expansion under BBT is an increase in the size of that object. If you prefer strings, fabrics, levels or other theory creating a curved space scenario, they are all with in that object, which should be all effected by any increase in the total volume.

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In this view, the Big Bang that started the baby universe growing 14 billion years ago blew up only three of space’s dimensions, leaving the rest tiny. Many theorists today believe that 6 or 7 such unseen dimensions await discovery.

 

Of course, it’s not as simple as that. An extra dimension of time is not enough. You also need an additional dimension of space

http://www.physorg.com/news98468776.html

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Martin;

There is an explosion of interest in understanding the U (Cosmology/Astronomy), which can be seen anyplace discussion is permitted. These are primarily folks, questioning the BBT or in some way the Creationist ideas inferred by their church or schools. While your post offering explanations are interesting, certainly enlightening, they offer little or no room for objectionable comments. We had this in the 50's, 60's, with an end result in acceptance of BBT in the first place, but there may be something to beyond BBT or some compromise between SSU, BBT, if nothing other than matter or what is today could have and logically should have, in some manner has always existed. Like it or not all theory, think about 10 or so being studied/explored on how a Universe (as we know it) came into existance, starts from the premise that something had to exist before....