View Poll Results: Is Lawrence Krauss right about the universe being flat?
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'A Universe From Nothing' by Lawrence Krauss, AAI 2009


by Schlofster
Tags: universe expansion
Schlofster
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#1
Oct28-09, 05:22 AM
P: 28
I started this thread a while ago talking about Stephen Hawking's "No Boundary Condition".

I think that I finally got a handle on it, but now Lawrence Krauss has discussed here why he thinks that the universe is not closed, but flat, and he says by implication, 'infinite in spatial extent'.
(he also claims to have empirical evidence of the flatness of space-time on the largest scales)

I don't understand how he can reconcile this with the big bang (which he also seems to accept).
If the universe is infinite in spatial extent, at what point did it become infinite, because when the universe was 1 second old, it was not infinitely large (I think that this is the scientifically accepted view).
He is obviously a widely respected physicist, and I am not a physicist, so I expect that I just don't understand what he is saying.

Could anyone explain it to me, or can it not be expressed in natural language?

Thanks,
Schlofster
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mikeph
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#2
Oct28-09, 05:49 AM
P: 1,199
Quote Quote by Schlofster View Post
If the universe is infinite in spatial extent, at what point did it become infinite, because when the universe was 1 second old, it was not infinitely large (I think that this is the scientifically accepted view).
I don't think this is scientifically accepted. When the universe was 1 second old, all we can say is the scale factor was a lot smaller than today, nothing about the size of the universe.

For me the idea of an infinite universe is troubling when you think what happens at time zero, but for all positive times there is no mathematical problem, an infinite space can still expand as much as it likes. And when you think about time zero with whatever perspective of the size of the universe you will be uncomfortable thinking about it, so I don't think an infinite universe has any relative disadvantage from this perspective.
Schlofster
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#3
Oct28-09, 06:42 AM
P: 28
In the talk, he claims that they have used mathematical calculations to calculate the mass of the universe, and he claims that most of the mass in the universe is as a result of virtual particles "popping in and out of existence" in empty space.
Considering this, and since he is able to calculate the mass of the universe to be a finite quantity, how is it then possible to say that the universe is infinite in spatial extent, because this then implies that the mass of the universe should be infinite since empty space itself constitutes most of the mass of the universe?
Is my logic flawed?
If it is, please show me where, because I would really like to understand this if it is possible to express the answer in natural language.

Many thanks,
Schlofster

mikeph
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#4
Oct28-09, 07:13 AM
P: 1,199

'A Universe From Nothing' by Lawrence Krauss, AAI 2009


Are you sure he says mass and not density? I can't watch it because I'm in a library.

Your logic seems fine here.
qraal
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#5
Oct28-09, 04:45 PM
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Quote Quote by Schlofster View Post
In the talk, he claims that they have used mathematical calculations to calculate the mass of the universe, and he claims that most of the mass in the universe is as a result of virtual particles "popping in and out of existence" in empty space.
Considering this, and since he is able to calculate the mass of the universe to be a finite quantity, how is it then possible to say that the universe is infinite in spatial extent, because this then implies that the mass of the universe should be infinite since empty space itself constitutes most of the mass of the universe?
Is my logic flawed?
If it is, please show me where, because I would really like to understand this if it is possible to express the answer in natural language.

Many thanks,
Schlofster
An infinite Universe is merely a possibility of the chosen topology - in this case a 'flat' Universe. There's no evidence that it is infinite, merely philosophical presumption.
marcus
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#6
Oct28-09, 06:47 PM
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I saw that talk several days ago.
It is delightful. Some very funny remarks, great quotes----sly pokes at this and that.
I would urge everybody to watch the video, just for entertainment!

However it is scientifically so sloppy as to be almost useless to us in Cosmo forum.

Krauss is a worldclass cosmologist, but he is talking at a total layman level and, as he explicitly says, nothing is to be taken seriously---he calls his statements lies because they are purely verbal---no rigorous definitions, just impressionistic approximate language.
He uses the word "lies" in reference to his own statements, explaining that what he is saying is not mathematical, not quantitative, imprecise.

So it is a wonderful talk but don't try to translate anything into hard empirical fact.

There is no evidence that the U. is spatially flat. Only that it is NEARLY so. The current 95% confidence interval on the curvature allows for finite volume spacetime with circumference lower bound of 600 billion lightyears.
Krauss does not indicate he has anything different from the most recent WMAP report, that you or I can get from NASA or from arxiv.org.
When talking to a complete nonscientist, nonmathy audience we can understand saying that that the U is spatially flat and spatially infinite. But you cannot as a scientist talking to other scientists maintain this. It is possible. It is one consistent interpretation. But another equally good interpretation of the data is that space is finite volume and if you could freeze expansion so that you could make the round trip, it would take 600 billion years traveling at the speed of light.

His scholarly papers on arxiv.org are different from his stand-up entertainer pop-talk to general audience. I'm a fan of Krauss. He is first class in either category---pop-sci or real-sci. More power to him.
Chalnoth
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#7
Oct29-09, 12:36 AM
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Quote Quote by marcus View Post
I saw that talk several days ago.
It is delightful. Some very funny remarks, great quotes----sly pokes at this and that.
I would urge everybody to watch the video, just for entertainment!

However it is scientifically so sloppy as to be almost useless to us in Cosmo forum.

Krauss is a worldclass cosmologist, but he is talking at a total layman level and, as he explicitly says, nothing is to be taken seriously---he calls his statements lies because they are purely verbal---no rigorous definitions, just impressionistic approximate language.
He uses the word "lies" in reference to his own statements, explaining that what he is saying is not mathematical, not quantitative, imprecise.

So it is a wonderful talk but don't try to translate anything into hard empirical fact.

There is no evidence that the U. is spatially flat. Only that it is NEARLY so. The current 95% confidence interval on the curvature allows for finite volume spacetime with circumference lower bound of 600 billion lightyears.
Krauss does not indicate he has anything different from the most recent WMAP report, that you or I can get from NASA or from arxiv.org.
When talking to a complete nonscientist, nonmathy audience we can understand saying that that the U is spatially flat and spatially infinite. But you cannot as a scientist talking to other scientists maintain this. It is possible. It is one consistent interpretation. But another equally good interpretation of the data is that space is finite volume and if you could freeze expansion so that you could make the round trip, it would take 600 billion years traveling at the speed of light.

His scholarly papers on arxiv.org are different from his stand-up entertainer pop-talk to general audience. I'm a fan of Krauss. He is first class in either category---pop-sci or real-sci. More power to him.
Yes, definitely. It's also worth mentioning that he also listed out the current experimental limits at about 1% (which is correct).
robertm
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#8
Oct29-09, 07:41 PM
P: 290
I was going to ask about this as well.

It seemed to me that he is particular to the (relative) theoretical simplicities that a zero-sum universe would provide.

I generally enjoy Kruass, and I did quite enjoy this talk, but I just can not imagine that he thought a general audience would not be able to comprehend the idea that he is biased toward the flat case, which does fit the current data, but that more data is needed in order to make any definite statement either way (flat or closed). Especially since, as far as I understand the data, the closed universe seems to be slightly favoured.

He specifically and deliberately stated multiple times that the universe IS flat; it just seems to me to be a sloppy and unnecessary short cut that is guaranteed to cause confusion in his target audience.

But I guess this sort of thing is just what you get, even from world class popularizing.
Chalnoth
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#9
Oct29-09, 08:26 PM
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For all practical purposes, as long as the dark energy continues to act much like a cosmological constant, our universe might as well be perfectly flat.
Schlofster
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#10
Oct30-09, 03:28 AM
P: 28
I am sorry to ask, (maybe this is because I have only done some undergrad physics and therefore don't understand your answer) but I still don't see how Prof. Krauss can claim to conclude that the U is infinite in spatial extent when he also claims that the U has a finite mass, and he also claims that completely empty space accounts for 70% of the mass of the U.
This still seems to me to be a non sequitur, because the empirical measurements of the finite mass of the U must then imply that the U must be finite in spatial extent (using my admittedly simple logic).
Since Krauss says that a flat U would be infinite in spatial extent, this must then imply that the universe must be closed (again using my admittedly simple logic).

Do I make any sense at all, or should I just give up trying to use my folk logic to understand how the conclusions cosmology are internally consistent?

Were I to show this video to my theist friends (I am not a theist), I think that it would seriously damage the reputation of science in their eyes - a first class cosmologist making logically (folk logic of course) inconsistent statements.
Schlofster
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#11
Oct30-09, 03:31 AM
P: 28
I think that I might be starting to see a pattern emerge - it seems to me that the intellectual abilities that scientists like Krauss are so far beyond what ordinary humans are capable of, he cant even articulate them at all in a way is intelligible by the majority of humans on this planet.
Ordinary humans would understandably respond with incredulity, and since they pay his salary, I suggest that people like him should only make statements that are logically intelligible ordinary people.
I think that public lectures like this just serve to polarize the voting public, against science.

I am rather interested though in what the evolutionary consequences of this cavernous gap between the intelligentsia and the rest of the human population would be.
Is it possible that we eventually see a divergence in the species - this may also be accelerated if people are selected for establishing a human colony on another planet like Mars.
Presumably the criteria for selecting the people for this mission would be heavily biased in favour of intellect.
Chalnoth
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#12
Oct30-09, 03:48 AM
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Quote Quote by Schlofster View Post
I am sorry to ask, (maybe this is because I have only done some undergrad physics and therefore don't understand your answer) but I still don't see how Prof. Krauss can claim to conclude that the U is infinite in spatial extent when he also claims that the U has a finite mass, and he also claims that completely empty space accounts for 70% of the mass of the U.
I don't see how he's claimed any of these things. Except that last one, which is basically what we understand the cosmological constant to be.

Quote Quote by Schlofster View Post
This still seems to me to be a non sequitur, because the empirical measurements of the finite mass of the U must then imply that the U must be finite in spatial extent (using my admittedly simple logic).
Er, what? There is no such measurement that has been performed, because the limits of our ability to measure do not extend to the entire universe.
Chalnoth
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#13
Oct30-09, 04:01 AM
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Quote Quote by Schlofster View Post
I think that I might be starting to see a pattern emerge - it seems to me that the intellectual abilities that scientists like Krauss are so far beyond what ordinary humans are capable of, he cant even articulate them at all in a way is intelligible by the majority of humans on this planet.
It has nothing to do with that. It's a matter of language. What we understand the universe to be, as well as the experimental results that place limits on our universe's behavior, are placed in the extremely precise language of mathematics. It is unfortunate but simply true that most people don't understand this language, due to a lack of training, and also due to a lack of use. And so people, when attempting to engage the public, attempt to explain things in the language that people outside their own field understand: colloquial language.

But colloquial language isn't nearly as precise as mathematics. Many of the mathematical statements about what we currently know just don't have any meaning at all in colloquial language, and can't be translated. Various popularizers of science make use of different attempts at performing this imperfect translation. Many disagree on precisely how to do it, even in cases where there is no disagreement in the underlying science that is in the language of mathematics.

In the end, what this means is twofold:
1. You can't hope to have an actual understanding of the science unless you take the time (and it is quite a lot of time, unfortunately) to understand the mathematical language of the science in question. You can definitely get a vague impression, or some superficial understanding. But you can't hope for that understanding to be entirely accurate.
2. If you want to try to find fault with a theory, you really need to go to the only language in which it is accurately described: mathematics. Due to the inaccuracies of plain language, and due to the fact that plain language doesn't exactly describe the mathematics, you're more likely to find fault with the way in which the person translated from mathematics to plain language than with the underlying theory. The only way to be sure is to go to the underlying mathematics.

In sum, it's not about intelligence, it's about taking the time to understand the language of the science. Which few people have the time or take the time to do (as it generally takes years of study).
Schlofster
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#14
Nov4-09, 02:21 AM
P: 28
Quote Quote by Chalnoth View Post
In sum, it's not about intelligence, it's about taking the time to understand the language of the science. Which few people have the time or take the time to do (as it generally takes years of study).
Well, you seem to be implying here that most humans are born with the potential to understand the most advanced math that humanity has produced.
As far as I know, that is not accepted to be the case, but I do take your point - most humans pay very little attention to developing their mathematical skills resulting in the expected inability to understand the science.

In a way, this is congruent with my point above - If you know that the average person won't understand what you are saying and will think that it is illogical, then don't say it if they are paying your salary (even though they are the ones who are deficient)!
Unfair, I know :-(
Chalnoth
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Nov4-09, 02:55 AM
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Quote Quote by Schlofster View Post
Well, you seem to be implying here that most humans are born with the potential to understand the most advanced math that humanity has produced.
For the most part, yes, I think this is likely to be the case. However, let me stress that in terms of these theories, it is most definitely not necessary to understand the most advanced mathematics that humanity has produced. The mathematics behind what is being talked about in this thread, though more complex than most people are exposed to, are generally quite simple. They're nowhere near as complicated even as the mathematics you see in quantum field theory, let alone what the mathematicians generally work on. I would find it exceedingly strange that a student who could do well at basic algebra could fail to do well, given time and effort, at the mathematics required here.

Quote Quote by Schlofster View Post
In a way, this is congruent with my point above - If you know that the average person won't understand what you are saying and will think that it is illogical, then don't say it if they are paying your salary (even though they are the ones who are deficient)!
Unfair, I know :-(
Well, they won't necessarily think it's illogical. And I am perfectly happy to help people who want to understand to do so. I think it's great when people are curious about the science, and honestly want to know what's going on. Just bear in mind that scientists are not dummies, and I can virtually guarantee you that any objection you have ever thought of, if it is a valid objection, has already been thought of a thousand times over by scientists all over the world.

This was definitely my experience when I was training to be a scientist. When I was new at this, working as a young student, I had all sorts of ideas of how certain things might be wrong, or of potential alternative ideas that might be right. As it turned out, when I learned more, I found that every single one of my ideas was either blatantly and obviously wrong, or had already been developed, and in vastly more depth, by somebody else.

The only time amateurs really have much of any chance at all of contributing something novel is when a field is brand-new and still only has a very small number of people working on it, where the amateur is on relatively equal footing with everybody else because everybody in the field is an amateur. But this just isn't the case in modern cosmology.
Schlofster
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#16
Nov4-09, 03:03 AM
P: 28
nice reply - thanks - I put this question to Prof Krauss, and he responded to me, pointing out where I was going wrong.
I have asked him if I can post his reply here, I will do so if he gives me permission.
Schlofster
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#17
Nov4-09, 09:42 AM
P: 28
Quote Quote by schlofster
I am sorry to ask, (maybe this is because I have only done some undergrad physics and therefore don't understand your answer) but I still don't see how Prof. Krauss can claim to conclude that the U is infinite in spatial extent when he also claims that the U has a finite mass, and he also claims that completely empty space accounts for 70% of the mass of the U.
Quote Quote by Chalnoth View Post
I don't see how he's claimed any of these things. Except that last one, which is basically what we understand the cosmological constant to be.
Quote Quote by schlofster
This still seems to me to be a non sequitur, because the empirical measurements of the finite mass of the U must then imply that the U must be finite in spatial extent (using my admittedly simple logic).
Quote Quote by Chalnoth
Er, what? There is no such measurement that has been performed, because the limits of our ability to measure do not extend to the entire universe.
Well, I have transcribed some relevant sections of the talk, and it seems to me that my bewilderment by his contradictions is not irrational.

time index: 19:35
what could contribute a term like this, and we know the answer - nothing - by "nothing", I don't mean nothing, I mean nothing.
If you take empty space, and that means get rid of all the particles, all the radiation, absolutely everything,
so there is nothing there, if that nothing weighs something, then it contributes a term like this.


time index: 21:20
It turns out, most of the mass of the proton comes not from the quarks within the proton, but from the empty space between the quarks.
these fields produce about 90% of the mass of the proton, and since protons and neutrons are the dominant stuff in your body,
empty space is responsible for 90% of your mass.

time index: 23:48
we should test what the energy of empty space is, how do we do that? well we 'weigh' the universe,
how do we do that? well we stand on the shoulders of giants.

time index: 24:53
and the point is, we can use gravity to 'weigh' the universe including the weight of empty space

time index: 25:30
and an open universe would be infinite in spatial extent, as would a flat universe

time index: 40:20
but just like Goldilocks, in a flat universe, it is just right, in fact it is right now we know to an accuracy of better than 1 percent.
The universe is flat, it has zero total energy, and it could have begun from nothing, and I have written a piece,
although of course, I got a lot of hate mail, saying that in my mind, this answers this crazy question that religious people keep throwing out
which is: "Why is there something rather than nothing", the answer is: there had to be, if you have nothing in quantum mechanics, you will
always get something, it is that simple, it doesn't convince any of those people, but it is true.

time index: 41:01
Now, great, we know the universe is flat, but if you have been awake, 10 minutes ago I proved that the universe is open,
there is only 30% of the stuff in the universe needed to make it flat, where's that other 70%?
Well, if you put energy in empty space, so that empty space weighed something, you wouldn't see it, it is the empty space between the galaxies,
you're far away from those galaxies, you wouldn't see it.
But what would that empty space do if you put energy in it, well, produce a cosmological constant, that would cause the expansion of the universe
not to slow down over time, as any sensible universe would do, but to speed up over time.
In 1998, people measuring these supernovae at large distances to measure the Hubble diagram tried to measure what was happening at large distances
to see if the universe was slowing, well they all knew that the universe was slowing down, they wanted to measure how much.
This doesn't look like much, but it was a revolution in cosmology.
I can draw a straight line through that dataset there and bring the whole thing down and make it horizontal, and if the universe was slowing down,
these distant supernovae should have followed this curve.
Much to the surprise of the observers, the supernovae lay above the straight line, and the only way to explain this, well there is two ways,
either the data is wrong , which it usually is, or the universe is accelerating, speeding up.
And if just for fun, one believed it was speeding up, and one asked just how much energy would you have to put in empty space to make it speed up
by the amount we measure it, it is exactly the amount we are missing.
Everything holds together, our new picture of cosmology is that we live in a universe dominated by nothing.
The largest energy in the universe, 70% of the energy in the universe, resides in empty space, and we don't have the slightest idea why it is there.


Quote Quote by Chalnoth
Well, they won't necessarily think it's illogical.
A comment by Marcus seems appropriate to me:
Quote Quote by Marcus
However it is scientifically so sloppy as to be almost useless to us in Cosmo forum.
As far as I can see, it is not only scientifically sloppy, it is more broadly logically sloppy (the little matter of whether the universe is infinite in spatial extent is muddled here).
I understand that it is impossible to express the mathematical model in natural language while still maintaining logical consistency, but I feel that in this case, no attempt should be made, because it damages his reputation and the reputation of science in general in the eyes of non scientists.
Ich
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#18
Nov4-09, 10:01 AM
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And where's the contradiction? Where does he claim that the universe has a finite mass?
"we 'weigh' the universe" - is that the phrase which bothers you?


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