B How does emergent spacetime work?

[wolram]

TL;DR Summary

I have been reading a little about it but it doesent make sence to me

How can space time emerge from nothing, I mean nothing in the absolute case is voide of any thing, I can imagine the BB where there is a primordial plasma the expands and creates the matter and space, but space time from nothing is beyond me, me being stupid and uneducated.

 

[Weran]

Summary:: I have been reading a little about it but it doesent make sense to me

but space time from nothing is beyond me, me being stupid and uneducated.

Its not about you..no one knows the answer of that question

 

[weirdoguy]

How can space time emerge from nothing

And in what textbook or peer-reviewed paper did you read that it can emerge from nothing?

 

[PeterDonis]

I have been reading a little about it

Where? Please give a specific reference.

 

[wolram]

https://aip.scitation.org/doi/full/10.1063/1.4899081

However more recently

 

[wolram]

Well I thought that geometry was nothing, its just a mathmatical formula ie nothing

 

[weirdoguy]

I used a search option and it did not find the word "nothing" in your link.

 

[wolram]

I used a search option and it did not find the word "nothing" in your link.

? That was a draft I don't know how I posted it.

 

[PeterDonis]

thought that geometry was nothing, its just a mathmatical formula ie nothing

Don't confuse the mathematical formula with what it describes. The word "geometry" can be used to refer to both. For example, in the GR literature the term "spacetime geometry" is often used. That term is not referring to the mathematical formulas that physicists write down; it's referring to what those formulas describe, the real thing that is called "spacetime" and the real properties it has that we describe using the mathematical formulas of geometry.

 

[haushofer]

Afaik, in the emergent scenario space(time?) and its geometry emerges from yet unknown fundamental degrees of freedom. Just like Maxwell didn't know the details of atoms yet could derive thermodynamical properties via statistics, people now try to derive geometry from the quantum entanglement of the yet unknown "fundamental spacetime degrees of freedom".

"Nothing" enters nowhere. It didn't for Maxwell and co., and it doesn't here.

 

[phinds]

Lawrence Krauss wrote a whole book on the subject (A Universe From Nothing) but that's a pop-science presentation and if that's where you got it, you should not take it seriously.

 

[pinball1970]

Lawrence Krauss wrote a whole book on the subject (A Universe From Nothing) but that's a pop-science presentation and if that's where you got it, you should not take it seriously.

Is there nothing of value in that book?

 

[phinds]

Is there nothing of value in that book?

It's been quite a while since I read it and I don't really recall. I DO remember being very put off by his certitude about his central premise which is that the universe evolved from nothing. I don't even remember how, or if, he defined "nothing" and I considered his thesis just a personal opinion (HE feels that he "proved" it, but ... )

I would add, I find Krauss very entertaining, both in his TV appearances and in his books, but he IS a bit of a pain sometimes.

 

[pinball1970]

It's been quite a while since I read it and I don't really recall. I DO remember being very put off by his certitude about his central premise which is that the universe evolved from nothing. I don't even remember how, or if, he defined "nothing" and I considered his thesis just a personal opinion (HE feels that he "proved" it, but ... )

I would add, I find Krauss very entertaining, both in his TV appearances and in his books, but he IS a bit of a pain sometimes.

He uses the word plausible a lot both in the book and presentations on it.
An emphasis on the evidence that suggests the observable universe is flat is made a lot.
That's what I remember but I'll have to read it again.

If the universe is infinite then I suppose time has always been and did not need to to emerge in the first place? Or space?

 

[phinds]

If the universe is infinite then I suppose time has always been and did not need to to emerge in the first place? Or space?

When you see "The universe may be infinite", it means in EXTENT, not in duration, so your logic is based on a mistaken premise.

 

[pinball1970]

When you see "The universe may be infinite", it means in EXTENT, not in duration, so your logic is based on a mistaken premise.

So time could be emergent but space may not be?
Ok.
Something to think about.

 

[windy miller]

I think there is a some confusion here, there are serious suggestions that the universe evolved from nothing , Krauss just popularised the idea but in a academic form you can read this paper here:
https://www.sciencedirect.com/science/article/abs/pii/0370269382908668

There is a different idea going around where space and time are emergent , in this sense of not fundamental. I think this is a separate idea and nothing to do with the paper I have linked to above. If anyone disagrees let me know, I have heard some people say it is emergent from entanglement but maybe someone can explain how this is supposed to work, as I understood entanglement is between particles, so are particles supposed to be fundamental?

 

[PeterDonis]

So time could be emergent but space may not be?

No. Whether or not spacetime is emergent from something more fundamental is independent of whether or not the spacetime that describes our universe is infinite in spatial extent or infinite in time extent.

 

[zoki85]

From "nothing"? If it is emergent, it's from something but they don't know what that could be. Calling it "nothing" is wrong.

 

[haushofer]

Is there nothing of value in that book?

For a critical view, see

https://arxiv.org/abs/1405.6091

 

[haushofer]

From "nothing"? If it is emergent, it's from something but they don't know what that could be. Calling it "nothing" is wrong.

"Nothing" in itself is an inconsistent term. But if you want to assign something to it, the quantumvacuum of spacetime is not such a bad choice. A better approach to "nothing" is hard to find ;)

 

[pinball1970]

For a critical view, see

https://arxiv.org/abs/1405.6091

I think I have seen this before. Too technical for from memory but I will give it a go

 

[pinball1970]

For a critical view, see

https://arxiv.org/abs/1405.6091

Still way to technical for me though

 

[haushofer]

Well, my impression of the book: it contains nice cosmology at the popular level and interesting ideas, but steps over many subtleties way too easy and pretends way too much. The praise of Dawkins in the forword (comparing it to Darwin's Origin of Species) is simply ridiculous.

In the end, Krauss' claim that we don't need god to explain the universe is not even wrong. It wasn't a problem in the first place, and the proposed solution for this non-existent problem is highly hypothetical and poorly understood. Admitting this is plain and simple intellectual integrity.

 

[DAH]

My knowledge in physics/cosmology is very basic and my math is even worse, but I've always liked the idea of a universe from nothing. I think this is partly due to me being an atheist (no need for a creator), and also from my basic understanding of how the universe works. The universe seems to be made up of positives and negatives, like energies and charges, where the sum of these properties is zero.

Also, i think experiments have shown that the vacuum of space is filled with particle/antiparticle pairs being created from the vacuum (borrowing energy from nothing) and then annihilating and paying the energy back to the vacuum, is that correct?

Most people think of 'nothing' as the vacuum of space where no matter/energy is present, but for me, a true nothingness would be no matter, no radiation, no time and no spatial dimensions. I don't think we can comprehend what that 'true nothingness' is because we only know of something.

 

[PeterDonis]

i think experiments have shown that the vacuum of space is filled with particle/antiparticle pairs being created from the vacuum (borrowing energy from nothing) and then annihilating and paying the energy back to the vacuum, is that correct?

Not really. See this Insights article:

https://www.physicsforums.com/insights/vacuum-fluctuation-myth/

 

[DAH]

Thanks for that link, very interesting, however I'm still a bit confused as to whether the particle/anti-particle pairs are just a myth or they really do exist, even if it's just for a fraction of a second. Also, from the link i branched off to another article on Hawking radiation and found that the virtual particles (if they exist) have positive and negative energy. Apparently the particles are separated at the event horizon and the negative energy always falls in leaving the positive particle outside and energy is conserved.
http://carlip.physics.ucdavis.edu/#Hawkrad

Does that mean the virtual anti-particle has negative mass (Eg. -1 kg)?
If so, would you have any links on negative mass?

 

[phinds]

Also, from the link i branched off to another article on Hawking radiation and found that the virtual particles (if they exist) have positive and negative energy.

Total misconception, unfortunately propagated by Hawking himself who said specifically that the "particle pair" explanation of Hawking radiation is just a heuristic that was the best he could do to express in English something that really can only be expressed in math. It is NOT to be taken seriously as an actual description of what happens.

 

[phinds]

If so, would you have any links on negative mass?

Google is your friend https://en.wikipedia.org/wiki/Negative_mass

 

[PeterDonis]

Google is your friend https://en.wikipedia.org/wiki/Negative_mass

This has nothing whatever to do with virtual particles or the (highly heuristic and often misleading) viewpoint in which some virtual particles have negative energy. Please don't confuse the OP any further.

 

[PeterDonis]

I'm still a bit confused as to whether the particle/anti-particle pairs are just a myth or they really do exist, even if it's just for a fraction of a second.

And the answer to this is, neither. Virtual particles are a name for a particular mathematical feature of a particular mathematical approximation used in quantum field theory. (The simplest way I know of to point at this feature is to say that virtual particles are internal lines in Feynman diagrams.) So virtual particles are not a myth, because the mathematical approximation I refer to is really used and can make real predictions that match experiments. But virtual particles don't "really exist" either, because they can never be observed directly (that's what internal in "internal lines in Feynman diagrams" means) and the mathematical feature is part of a specific approximation scheme which is not the only mathematical way to do quantum field theory. So the question you are asking is really the wrong question; you should not even be thinking in terms of whether virtual particles "exist" or not.

virtual particles (if they exist) have positive and negative energy

While there is a sense in which this can be said to be the case, it is open to the same objections that I gave above to asking the general question of whether virtual particles "exist" or not.

Does that mean the virtual anti-particle has negative mass (Eg. -1 kg)?

Not in any useful sense.

 

[phinds]

This has nothing whatever to do with virtual particles or the (highly heuristic and often misleading) viewpoint in which some virtual particles have negative energy. Please don't confuse the OP any further.

He asked for a link to negative energy. I gave him one.

 

[PeterDonis]

He asked for a link to negative energy.

He asked for a link about negative mass in relation to virtual particles. That's not what you gave him. The concept of "negative mass" described in the link you gave has nothing whatever to do with virtual particles and is not the same concept as the concept of "virtual particles having negative energy" that was referred to in the Carlip article the OP linked to when he asked about negative mass. As I said, please don't confuse the OP further.

 

[valenumr]

And the answer to this is, neither. Virtual particles are a name for a particular mathematical feature of a particular mathematical approximation used in quantum field theory. (The simplest way I know of to point at this feature is to say that virtual particles are internal lines in Feynman diagrams.) So virtual particles are not a myth, because the mathematical approximation I refer to is really used and can make real predictions that match experiments. But virtual particles don't "really exist" either, because they can never be observed directly (that's what internal in "internal lines in Feynman diagrams" means) and the mathematical feature is part of a specific approximation scheme which is not the only mathematical way to do quantum field theory. So the question you are asking is really the wrong question; you should not even be thinking in terms of whether virtual particles "exist" or not.
While there is a sense in which this can be said to be the case, it is open to the same objections that I gave above to asking the general question of whether virtual particles "exist" or not.
Not in any useful sense.

I like to think of imaginary numbers as an analogy. I've never had 3i apples, but the concept is incredibly useful mathematically. Heck, even negative numbers were considered absurd until people started lending money. ..

 

[PeterDonis]

I've never had 3i apples, but the concept is incredibly useful mathematically. Heck, even negative numbers were considered absurd until people started lending money. ..

In other words, what kinds of numbers are going to be useful depends on the particular application. Yes, that's true.

In the particular application under discussion in this thread, namely General Relativity, negative numbers for mass has a very specific physical meaning, which does not apply to virtual particles.