View Poll Results: Is Lawrence Krauss right about the universe being flat?  
Yes  12  41.38%  
No  17  58.62%  
Voters: 29. You may not vote on this poll 

#19
Nov409, 10:30 AM

P: 1,160

I voted "Yes" meaning the Minkowski spacetime with the gravitational filed to be physical one similar to other physical fields rather than variable curvature of the Riemann spacetime where not additive conservation laws are possible.




#20
Nov409, 12:42 PM

P: 28

what I said is that most of the mass of protons and neutrons can be attributed to virtual particles.. it is that mass that we can calculate using the theory of the strong interaction and powerful computers..
_______________________________ Lawrence M. Krauss Foundation Professor Director, Origins Initiative CoDirector, Cosmology Initiative ARIZONA STATE UNIVERSITY College of Liberal Arts and Sciences School of Earth and Space Exploration http://krauss.faculty.asu.edu On Nov 3, 2009, at 5:04 PM, Jessica Lee wrote:  Forwarded Message Date: Wed, 28 Oct 2009 06:48:23 0700 Subject: A Question For Prof Krauss. Hi Jessica, Please could I ask you to send this question on to Prof. Krauss? Hi Prof Krauss, I loved your recent public lecture <http://www.youtube.com/watch?v=7ImvlS8PLIo> at AAI 2009, but I don't understand something, and I was hoping that you might be able to spare a few moments to clear it up for me. First of all let me state that I am no physicist, so I am rather certain that my misunderstanding is due to an incomplete grasp of the mathematical model that you attempt to describe in natural language. I do understand that it is actually impossible to do this since the mathematical model cannot be expressed in natural language. In the lecture you say that you have calculated the mass of the universe, and have calculated that most of the mass in the universe is as a result of virtual particles "popping in and out of existence" in empty space, while matter particles constitute a very small fraction of the mass of the universe. Considering this, and since you are able to calculate the mass of the universe to be a finite quantity, it seems to me that a conclusion that the universe is infinite in spatial extent would be logically incompatible with a universe of finite mass. I say this because if empty space itself constitutes most of the mass of the universe, then if the amount of empty space is infinite, then the mass of the universe must also be infinite. Thanks very much & kind regards,  End of Forwarded Message 



#21
Nov409, 01:04 PM

P: 28

What also bothers me is I cant show this lecture to any theists or deists because he says: "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. They will just respond: where did the quantum mechanics come from? When in reality, he has shown that there are 2 different definitions of "nothing", I think that he means the physics definition where empty space can be called "nothing", and this may be empty space in some wider reality before the universe was created in the big bang. This would confuse the layman, because they would tend to use their own definition of nothing  which really is nothing  no empty space, no quantum field or fluctuations  literally nothing. I think that his mixing of language here will really confuse the general public. I know that he qualifies all of this by saying that you must not take him literally all the time because he cant express the mathematical model in natural language, but I am asking whether this kind of confusing talk in natural language is a good idea in a world where people often dismiss scientists as being biased against any deistic solutions. (I am neither a deist nor a theist) 



#22
Nov409, 02:08 PM

Sci Advisor
P: 1,883

Read that text again with this in mind. I think you'll find that at no place he says something that can convincingly be interpreted as the mass of the universe being finite. You will also find that the wording "...of the mass of the universe..."  which could be such a hint  is yours, not his. For the theist debate: Don't believe that physics can prove that there must be something rather than nothing. At least not yet, and maybe such a proof is impossibe. It's not the fault of the theists if they don't buy into it. 



#23
Nov409, 02:14 PM

P: 28





#24
Nov609, 07:37 AM

P: 28

I have to now concede that what he is doing is very important  taking science to the masses and by making it accessible by sacrificing accuracy and coherency for in favour of creating an immersive, entertaining experience, inducing the awe and wonder in the audience that our universe is worthy of. 



#25
Nov709, 02:54 AM

Sci Advisor
PF Gold
P: 9,173

Flat looks very attractive given current observational evidence. What flat means is subject to interpretation. There are a number of ways to induce this impression that are model dependent.




#26
Nov709, 04:09 PM

Sci Advisor
P: 1,883

Sorry, OT. 



#27
Nov709, 04:20 PM

P: 1,444

My take  while enjoyable and informative  Krauss pontificates at several places which are, as pointed out in the above posts, not yet established  in particular, the notion of an evolving infinite universe. Perhaps Asympotical Flatness leads to a spatal distension that approaches infinity at some infinite time  its hard to imagine an infinite universe that instantly sprang into being like Athena emerging full grown from the head of Zeus. Seems like Krauss has an agenda  that of selling Flat Universes.




#28
Nov809, 04:06 AM

Sci Advisor
PF Gold
P: 9,173

LOL, Ich. Curved is very comely. A lot if it has to do with philosophy and aesthetics. In a finite universe of finite age, you are inevitably faced with a choice between a unverse from nothing, or a cyclical universe. It is a difficult choice. Something from nothing seems illogical, but, so does a universe that can reincarnate itself in perpetuity  both forward and backward in time  without gaining or losing a single quark in the process.. An infinitely old and large universe, a third option, just doesn't work for me without a compelling solution to Olber's Paradox. There is also a fourth option  parallel universes. This, imo, is fairy dust until someone figures out how to detect them.




#29
Nov809, 04:58 AM

P: 82

I voted No. Why? Shortly because:
1. The BB Theory say that the Universe is not expanding in space, instead the space of Universe is expanding. At the beginning the Universe has a finite and little "amount" of space. An "outside" space doesn't exist. 2. The expansion of Universe is without center and without bounders. 3. I can't imagine a flat shape without bounders (name me a 2D flat geometrical shape without bounders and than extend it to 3D). So, my believe is that the Universe it is flat only at our observational scale. It is like a humane eye observation of Earth shape: it just look like to be flat. 



#30
Nov809, 05:16 AM

Sci Advisor
P: 4,721

But really, I don't think anybody genuinely believes that our universe is perfectly flat. Just that it is very, very close to flat. And the generallyaccepted explanation is inflation, which drives the universe to near perfect flatness in a tiny fraction of a second. 



#31
Nov809, 07:36 AM

P: 82

Yes, maybe a torus is mathematically flat shape but is a strange kind: a torus shape Universe is closed (going on any direction you will finally arrive at the same point) but for each direction other "diameter" of Universe exist. So, it seems like each direction have its own properties.
In our Universe all directions seem to have the same properties, at least until now. Or I don't know well? 



#32
Nov809, 07:39 AM

Sci Advisor
P: 4,721

Closed is a statement about curvature. Whether or not the universe wraps back on itself is a statement about topology. It is perfectly possible to have a flat universe with a topology that wraps back on itself. Just as it is, in principle, possible to have a closed universe that doesn't extend far enough to wrap back on itself. 



#33
Nov809, 07:47 AM

P: 82

Thank you for yours answers.
Please tell me, what is the meaning of "flat" for cosmology? 



#34
Nov809, 08:07 AM

Sci Advisor
P: 4,721

If you draw a triangle on a "closed" surface, its angles add up to greater than 180 degrees. For example, if you draw a triangle on a sphere by starting from the north pole, drawing down to th equator, then across the equator a quarter of the way around, then back to the north pole, you've just made a triangle where each angle is a right angle: you've made a triangle whose angles sum to 270 degrees. If you draw a triangle on an "open" surface, the reverse is true: the angles sum to less than 180 degrees. A saddle is an example of a surface that has this property. When we're talking about the curvature of the universe, this is what we mean: we draw triangles by looking at the passage of light from place to place in the universe. The angles that they make tell us what the overall curvature is. And it's very very close to flat. 



#35
Nov809, 08:18 AM

P: 82

Thank you again, but I already knew that.
My question was about that: to measure the flatness of Universe the mean density of Universe if measured and it is compared with critical density. If I understood correct, this is how we can tell today that the Universe is "very close to flat". But, every popular article about this subject stop here. I look for article that discuss about the effective shape of Universe for the flat case. 



#36
Nov809, 11:21 AM

Sci Advisor
P: 4,721

The "triangle" drawn from the CMB is composed of the typical distance between the "acoustic peaks" which is set by the age of the universe at the time the CMB was emitted. Comparing this distance to the angle that we see and the distance to the CMB gives us our triangle. The "triangle" drawn from BAO measurements comes from the fact that these measurements are measuring a typical distance between galaxies in the more nearby universe, a distance that is correlated to the same distance seen in the CMB. We can thus draw a different triangle as the typical separation between galaxies compared to the distance to those galaxies and their angular separation. By contrast, other measurements of the contents of the universe that don't end up effectively drawing triangles, such as supernovae to measure the expansion rate as a function of time, don't measure the curvature at all. 


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