SA: What Is Spacetime Really Made Of?

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SA: What Is Spacetime Really Made Of?

#1

Post by notFritzArgelander »


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Re: SA: What Is Spacetime Really Made Of?

#2

Post by Michael131313 »


Well that made my head spin. 🤯
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Re: SA: What Is Spacetime Really Made Of?

#3

Post by notFritzArgelander »


Michael131313 wrote: ↑Tue Jan 25, 2022 2:24 am Well that made my head spin. 🤯
It's also spinning the heads of the physics folks. :)
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Re: SA: What Is Spacetime Really Made Of?

#4

Post by WilliamPaolini »


"Their work raised the question of whether time and space are somehow illusory..." :tools-hammerdrill: I've been told that before. May just be so.

Now that was an interesting article :text-thankyouyellow:
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Re: SA: What Is Spacetime Really Made Of?

#5

Post by notFritzArgelander »


WilliamPaolini wrote: ↑Tue Jan 25, 2022 2:57 am "Their work raised the question of whether time and space are somehow illusory..." :tools-hammerdrill: I've been told that before. May just be so.

Now that was an interesting article :text-thankyouyellow:
It is a nice review and overview that at least mentions the three leading candidates for an emergent spacetime. I would have preferred more balance between, string theory, quantum loops and causal sets. But it fairly represents the consensus in terms of popularity.

Back at the old site we used to have a sticky thread on astrophysical videos. A superb, but long one (~1.25 hrs) was a public lecture by Fay Dowker discussing thermodynamics of BHs and causal set theory. There is an argument late in the talk, (~48minutes) handwaving to be sure, the estimates the value of the cosmological constant and the expansion of the universe.

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Re: SA: What Is Spacetime Really Made Of?

#6

Post by ThinkerX »


hmm...

1 - I was under the impression Fritz has 'issues' with Susskind, or at least aspects of String Theory.

2 - If space and time are emergent from 'something else,' then the 'one step removed' sensory/perception issue could become significant. It would mean that key elements of the universe are beyond our ability to perceive. At least that would be my take.

3 - the notion of immensely large (infinite?) spaces arising from the 'folding' (yes, bad word choice) of infinitesimally small ones makes me wonder if our entire universe is but a 'gem' on the shelf of a Great Old One. Or it approaches the threshold of matters as much philosophic and theological as they pertain to physics. Which could lead to claims of 'category error.'
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Re: SA: What Is Spacetime Really Made Of?

#7

Post by notFritzArgelander »


ThinkerX wrote: ↑Tue Jan 25, 2022 5:32 am hmm...

1 - I was under the impression Fritz has 'issues' with Susskind, or at least aspects of String Theory.
That is correct with regard to two points:
a) the absolute necessity of Supersymmetric particles as partners to the particles of the Standard Model is required for string theory to work mathematically, none are observed (yet?)
b) the addition of the multiverse interpretation to randomly generate Nature's coupling constants is lazy physics IMO however the recent thread viewtopic.php?f=74&t=22297&p=183649&hil ... es#p183649 indicates that this of my objections might be overcome.
2 - If space and time are emergent from 'something else,' then the 'one step removed' sensory/perception issue could become significant. It would mean that key elements of the universe are beyond our ability to perceive. At least that would be my take.
It has been my take too ever since I read Kant. Space and time are the forms by which we order our perceptions. We NEVER perceive things as they ARE, only phenomena as they appear.
3 - the notion of immensely large (infinite?) spaces arising from the 'folding' (yes, bad word choice) of infinitesimally small ones makes me wonder if our entire universe is but a 'gem' on the shelf of a Great Old One. Or it approaches the threshold of matters as much philosophic and theological as they pertain to physics. Which could lead to claims of 'category error.'
It is a category error to posit in science something which has no observable consequence and cannot be tested. :) So I'll leave that to the theologians. ;)
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Re: SA: What Is Spacetime Really Made Of?

#8

Post by Greenman »


Having read that I believe the answer is 42. :D
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Re: SA: What Is Spacetime Really Made Of?

#9

Post by Michael131313 »


Thanks you guys for the interesting thread. Very Buddist of you nFA. "It has been my take too ever since I read Kant. Space and time are the forms by which we order our perceptions. We NEVER perceive things as they ARE, only phenomena as they appear"
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Re: SA: What Is Spacetime Really Made Of?

#10

Post by notFritzArgelander »


Michael131313 wrote: ↑Wed Jan 26, 2022 3:14 am Thanks you guys for the interesting thread. Very Buddist of you nFA. "It has been my take too ever since I read Kant. Space and time are the forms by which we order our perceptions. We NEVER perceive things as they ARE, only phenomena as they appear"
Well, I don't know. :shrug: While I would not deny Buddhist readings and practices, Kant was a Lutheran of pietist leanings. :)
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Re: SA: What Is Spacetime Really Made Of?

#11

Post by helicon »


Interesting article, thanks notFritz.
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Re: SA: What Is Spacetime Really Made Of?

#12

Post by pakarinen »


Greenman wrote: ↑Tue Jan 25, 2022 9:48 am Having read that I believe the answer is 42.
Ehhh, it's turtles all the way down.
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Re: SA: What Is Spacetime Really Made Of?

#13

Post by WilliamPaolini »


Michael131313 wrote: ↑Wed Jan 26, 2022 3:14 am Very Buddist of you nFA. "It has been my take too ever since I read Kant. Space and time are the forms by which we order our perceptions. We NEVER perceive things as they ARE, only phenomena as they appear"
Indeed!

"Nature can never be completely described, for such a description of Nature would have to duplicate Nature. No name can fully express what it represents. It is Nature itself, and not any part (or name or description) abstracted from Nature, which is the ultimate source of all that happens... If Nature is inexpressible, he who desires to know Nature as it is in itself will not try to express it in words. To try to express the inexpressible leads one to make distinctions which are unreal. Although the existence of Nature and a description of that existence are two different things, yet they are also the same. For both are ways of existing. That is, a description of existence must have its own existence, which is different from the existence of that which it describes; and so again we have to recognize an existence which cannot be described." --Lao Tzu, Tao te Ching; translated by Archie J. Bahm,1958

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Re: SA: What Is Spacetime Really Made Of?

#14

Post by chasmanian »


nFA,

"string theory, quantum loops and causal sets "

I just googled for a minute.
I am wondering about how each of these 3 theories treats Black Holes.
I read that String theory postulates Fuzzballs.
the other 2 sound like they go along with GR.

am I right to think that String theory does not go along with the Schwartzchild radius explanation for Black Holes,
but the other 2 theories do?
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Re: SA: What Is Spacetime Really Made Of?

#15

Post by notFritzArgelander »


chasmanian wrote: ↑Thu Jan 27, 2022 11:25 pm nFA,

"string theory, quantum loops and causal sets "

I just googled for a minute.
I am wondering about how each of these 3 theories treats Black Holes.
I read that String theory postulates Fuzzballs.
the other 2 sound like they go along with GR.

am I right to think that String theory does not go along with the Schwartzchild radius explanation for Black Holes,
but the other 2 theories do?
i'm afraid not. in the classical limit of low energies string theory goes along with the event horizon for BHs. it is only at very high energies that the fuzziness of a BH might be seen. the same goes for loop quantum gravity and causal sets: in the low energy limit agreement with GR is necessary.

loop quantum gravity at high energies has the novel property that BHs evolve into white holes.

https://physics.aps.org/articles/v11/127

causal set theory disturbs the GR picture of BHs by the least amount:

https://inspirehep.net/literature/803560
We explicitly compute the causal structure of the Schwarzschild black hole spacetime, by providing an algorithm to decide if any pair of events is causally related. The primary motivation for this study comes from discrete quantum gravity, in particular the causal set approach, in which the fundamental variables can be thought of as the causal ordering of randomly selected events in spacetime. This work opens the way to simulating non-conformally flat spacetimes within the causal set approach, which may allow one to study important questions such as black hole entropy and Hawking radiation on a full four dimensional causal set black hole.
i can come back to this later if needed?
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Re: SA: What Is Spacetime Really Made Of?

#16

Post by chasmanian »


thank you nFA.

fascinating, all you said.

I love the article in your first link. the second one is too hard for me.

this looks like super important stuff.
if you have any more thoughts, I'd love to hear any.
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Re: SA: What Is Spacetime Really Made Of?

#17

Post by notFritzArgelander »


chasmanian wrote: ↑Fri Jan 28, 2022 4:14 am thank you nFA.

fascinating, all you said.

I love the article in your first link. the second one is too hard for me.

this looks like super important stuff.
if you have any more thoughts, I'd love to hear any.
Well, there's not much, except that I think that the causal set stuff isn't as fully developed as strings and loops so it may be a while before we are very clear about how BHs fare in causal set theory.
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Re: SA: What Is Spacetime Really Made Of?

#18

Post by chasmanian »


thank you nFA.

side note:
so amazing that the Schwartzchild radius of the earth is ~9 mm.
so in inches, ~3/4 inch diameter sphere. incredible.
and fun thing to tell others.
science is amazing.
magical even.
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Re: SA: What Is Spacetime Really Made Of?

#19

Post by chasmanian »


nFA,

I have googled alot trying to find the answer before posting now.
still not clear about:

am I correct to say that the Schwartzchild radius of an object,
is the radius at which, if the object
exceeds a certain density, it will collapse into a black hole.

thank you for any thoughts,
Charlie
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Re: SA: What Is Spacetime Really Made Of?

#20

Post by notFritzArgelander »


chasmanian wrote: ↑Sat Jan 29, 2022 10:27 pm nFA,

I have googled alot trying to find the answer before posting now.
still not clear about:

am I correct to say that the Schwartzchild radius of an object,
is the radius at which, if the object
exceeds a certain density, it will collapse into a black hole.

thank you for any thoughts,
Charlie
Two complicated I think. It's rather the radius at which an event horizon is found for a given enclosed mass.
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