Physicists now question the fate of the Universe • Hacker News Board

Re: Physicists now question the fate of the Universe

#81

Post by thriftwy » Thu, May 23, 2024, 8:34 AM UTC

pdonis wrote: post #79

thriftwy wrote: post #72

Earlier quoted context omitted.

> However, this is still an open area of research That's exactly what I've feared. You just spent writing a full page of text how it takes several decades to understand the theory, then I ask a simplest of questions about it, one that any bright primary schooler will come up - and the understanding immediately implodes on itself because the answer is simply not there. All of these decades of studying led to a model t…

> I ask a simplest of questions about it, one that any bright primary schooler will come up - and the understanding immediately implodes on itself because the answer is simply not there. No, the answer is there, but it's not simple . Again, you want a quick sound bite: yes or no to your question. And reality is not like that . Reality is not simple sound bites. Reality is complicated and it takes work to figure out w…

> The density of stress-energy, for matter (or radiation, since you asked about light) is the same with the scale factor slightly smaller and the energy density slightly higher, as with the scale factor slightly larger and the energy density slightly smaller.

So you are saying, there is a semi-reversible process where energy and volume are correlated? That's what I've started with.

Should there actually be some specific amount of energy in place in order this density-to-scale transmutation to happen? What kinds of energy participate in it in our real world scenario? Does it depend on the specific local density (though I've already asked that)?

Re: Physicists now question the fate of the Universe

#82

Post by pdonis » Thu, May 23, 2024, 7:51 PM UTC

thriftwy wrote: post #81

pdonis wrote: post #79

Earlier quoted context omitted.

> I ask a simplest of questions about it, one that any bright primary schooler will come up - and the understanding immediately implodes on itself because the answer is simply not there. No, the answer is there, but it's not simple . Again, you want a quick sound bite: yes or no to your question. And reality is not like that . Reality is not simple sound bites. Reality is complicated and it takes work to figure out w…

> The density of stress-energy, for matter (or radiation, since you asked about light) is the same with the scale factor slightly smaller and the energy density slightly higher, as with the scale factor slightly larger and the energy density slightly smaller. So you are saying, there is a semi-reversible process where energy and volume are correlated? That's what I've started with. Should there actually be some speci…

> So you are saying, there is a semi-reversible process where energy and volume are correlated?

My original objection was to you thinking of it as a "process", or at least a process involving energy and volume. It's a relationship between stress-energy and spacetime geometry.

> Should there actually be some specific amount of energy in place in order this density-to-scale transmutation to happen?

There is no such "transmutation". That's not what's going on. Your questions aren't answerable because they are based on false premises.

At this point I've done my best to explain what is and isn't going on. All I can do is recommend reading more detailed treatments, which you can find in any cosmology textbook, or in briefer form in most GR textbooks. Sean Carroll's lecture notes on GR are available for free online [1], and Chapter 8 discusses the basics of our best current model of the universe in cosmology.

[1] https://arxiv.org/abs/gr-qc/9712019

Re: Physicists now question the fate of the Universe

#83

Post by DEADMINCE » Sat, May 25, 2024, 11:46 AM UTC

thriftwy wrote: post #81

pdonis wrote: post #79

Earlier quoted context omitted.

> I ask a simplest of questions about it, one that any bright primary schooler will come up - and the understanding immediately implodes on itself because the answer is simply not there. No, the answer is there, but it's not simple . Again, you want a quick sound bite: yes or no to your question. And reality is not like that . Reality is not simple sound bites. Reality is complicated and it takes work to figure out w…

> The density of stress-energy, for matter (or radiation, since you asked about light) is the same with the scale factor slightly smaller and the energy density slightly higher, as with the scale factor slightly larger and the energy density slightly smaller. So you are saying, there is a semi-reversible process where energy and volume are correlated? That's what I've started with. Should there actually be some speci…

At this point why not interact with an LLM to get a better base understanding? Disagreeing with someone more knowledgable whose answers you can't properly grok isn't a great way to learn, surely?

Re: Physicists now question the fate of the Universe

#84

Post by pdonis » Sun, May 26, 2024, 2:33 AM UTC

DEADMINCE wrote: post #83

thriftwy wrote: post #81

Earlier quoted context omitted.

> The density of stress-energy, for matter (or radiation, since you asked about light) is the same with the scale factor slightly smaller and the energy density slightly higher, as with the scale factor slightly larger and the energy density slightly smaller. So you are saying, there is a semi-reversible process where energy and volume are correlated? That's what I've started with. Should there actually be some speci…

At this point why not interact with an LLM to get a better base understanding? Disagreeing with someone more knowledgable whose answers you can't properly grok isn't a great way to learn, surely?

I would not advise trying to learn physics (or any subject, for that matter) from an LLM. They will confabulate confident sounding nonsense just as easily as they will give you reasonable information--and if you don't already know the subject, you won't be able to tell the difference.