How valid is the Block Universe theory?

[DarkloidNeos]

TL;DR

Citing an article that makes it sound like established fact given Einstein

https://nautil.us/welcome-to-the-block-universe-1278973

From what Max Tegmark and others in the article are making it sound like the model is a done deal, but I know others on here have mentioned that it's not really testable. How valid is it truly? I mean I understand how the model represents time, though I kinda agree with the ending criticisms in that we are making the mistake of taking a "gods eye" of the universe as though we can observe the whole thing at once. And directly too I might add.

 

[Ibix]

It's an interpretation, so not testable as far as we know. It's far and away the most popular interpretation, and fits well with the maths, but others are possible.

 

[PeterDonis]

This Insights article might be relevant:

Insights Thread 'The Block Universe - Refuting a Common Argument - Comments'

Nov 13, 2015

PeterDonis submitted a new PF Insights post

The Block Universe - Refuting a Common Argument

Continue reading the Original PF Insights Post.

• PeterDonis
• Argument Block Block universe Universe
• Replies: 146
• Forum: Special and General Relativity

• 

 

[PeterDonis]

@DarkloidNeos the article you reference, unfortunately, is not just presenting the speculations or opinions of various physicists it quotes as established fact (which they're not), it's a mismash of different speculations or opinions, not all of which actually have anything to do with the block universe interpretation of special relativity at all. This is, I'm afraid, common in pop science articles of this sort.

One good quick check: if the article doesn't reference any actual textbooks or peer-reviewed papers, be very, very wary. This article fails that check--its only references are to other pop science articles on the same site.

 

[DarkloidNeos]

One good quick check: if the article doesn't reference any actual textbooks or peer-reviewed papers, be very, very wary. This article fails that check--its only references are to other pop science articles on the same site.

Yeah I'm not sure what's good in terms of science and stuff like that. To me if it looks official then I generally believe it.

I tried to read the article you linked but I'm not sure I understood it. Is the reason it doesn't prove Block Time is because we don't directly perceive reality? I'm confused.

 

[PeterDonis]

if it looks official

What's your definition of "looks official"?

Is the reason it doesn't prove Block Time is because we don't directly perceive reality?

No, it's because what we directly perceive is our past light cone, not "now". For example, when you look at Alpha Centauri in the sky, you're not seeing it as it is "now". You're seeing it as it was 4.3 years ago--the time it took the light you're seeing now to travel from Alpha Centauri to your eye. So the fact that you're seeing Alpha Centauri now doesn't tell you what Alpha Centauri is doing "now". It doesn't even tell you for sure that Alpha Centauri is still there "now"--for example, it might have exploded after the light you're seeing was emitted.

The argument the article is refuting implicitly assumes that we can directly perceive things "now", or at least that what we directly perceive is sufficient to make "now" as real as what we directly perceive. But that's not the case. So the argument is based on a false premise.

 

[Dale]

Is the reason it doesn't prove Block Time is because we don't directly perceive reality?

The block universe is a specific interpretation of the theory of relativity. Like all interpretations, it makes no experimental predictions different from the theory. The theory of relativity can be experimentally verified or falsified. But all of the interpretations (including block universe) stand or fall together with the theory.

That said, the block universe is the most popular interpretation of relativity. It works well for both special and general relativity. But if you don’t like it then you are not forced to use it by either experiment or theory.

 

[Herman Trivilino]

Is the reason it doesn't prove Block Time is because we don't directly perceive reality? I'm confused.

A theory is used to make calculations. A theory is wrong if the results of its calculations don't match what we observe in Nature. The Block Universe isn't a theory. We can't use it to make calculations whose results can be compared to Nature's behavior. It is just a way of interpreting relativity theory, it's not an alternative to relativity theory so it can't be shown to be wrong, but it can't be shown to be right, either. It just gives us a framework for a way of thinking about relativity theory and the calculations we make using relativity theory.

In other words, you can take it or leave it. You've read some stuff written by people who made a choice to believe it. But it is just a choice.

 

[DaveC426913]

This Insights article might be relevant:

Insights Thread 'The Block Universe - Refuting a Common Argument - Comments'

Nov 13, 2015

PeterDonis submitted a new PF Insights post

The Block Universe - Refuting a Common Argument

Continue reading the Original PF Insights Post.

• PeterDonis
• Argument Block Block universe Universe
• Replies: 146
• Forum: Special and General Relativity

• 

I don't want to derail this thread. I'll jump in and, hopefully, back out.

The insight article seems to jump into the middle of an ongoing debate, the details of which seem to be taken for granted. So it's not very helpful for me (at least, not yet).

I have heard of the block universe interpretation. I had no idea that it was "the most popular interpretation of relativity".

I think have a basic idea of it (unchanging, fixed 4D universe, where our passage through that fourth dimension is experienced by us as the passage of time). And I have encountered the Andromeda Paradox before. But I'd like a get back up to speed on it.

Google searches keep returning with growing block universe, which may confuse more than clarify.

Suggestions on where I can read up on the block universe? A primer? (High school level math, at most please.)

 

[DarkloidNeos]

What's your definition of "looks official"?

Like the website looks clean and professional.

No, it's because what we directly perceive is our past light cone, not "now". For example, when you look at Alpha Centauri in the sky, you're not seeing it as it is "now". You're seeing it as it was 4.3 years ago--the time it took the light you're seeing now to travel from Alpha Centauri to your eye. So the fact that you're seeing Alpha Centauri now doesn't tell you what Alpha Centauri is doing "now". It doesn't even tell you for sure that Alpha Centauri is still there "now"--for example, it might have exploded after the light you're seeing was emitted.

The argument the article is refuting implicitly assumes that we can directly perceive things "now", or at least that what we directly perceive is sufficient to make "now" as real as what we directly perceive. But that's not the case. So the argument is based on a false premise.

Is this related to the sensory processing delay in the brain? I know the number is like around 0.083 seconds.

But then why would special relativity not prove that then? I know there is a delay to our sensation but I would think the math from the theory would supersede that.

 

[DarkloidNeos]

The block universe is a specific interpretation of the theory of relativity. Like all interpretations, it makes no experimental predictions different from the theory. The theory of relativity can be experimentally verified or falsified. But all of the interpretations (including block universe) stand or fall together with the theory.

That said, the block universe is the most popular interpretation of relativity. It works well for both special and general relativity. But if you don’t like it then you are not forced to use it by either experiment or theory.

Well the implications of it are what concern me, I was looking through a related thread below:

Insights Thread 'Does the Block Universe of Physics Mean Time is an Illusion?'

Sep 28, 2020

I have written many Insights (and coauthored an entire book) explaining how the puzzles, problems, and paradoxes of modern physics can be attributed to our dynamical bias and resolved by rising to Wilczek’s challenge [1]:
A recurring theme in natural philosophy is the tension between the God’s-eye [4D] view of reality comprehended as a whole and the ant’s-eye view of human consciousness, which senses a succession of events in time. Since the days of Isaac Newton, the ant’s-eye view has dominated fundamental physics. We divide our description of the world into dynamical laws that...

• RUTA
• Block Block universe Mean Physics Time Universe
• Replies: 56
• Forum: Special and General Relativity

• 

 

[Dale]

Well the implications of it are what concern me

Which specific implications? Some are probably parts of the interpretation (optional) but some are probably parts of the theory (not optional). It can be difficult to tell.

Is this related to the sensory processing delay in the brain?

No. Relativity is a theory of space and time in physics. It is not related to psychology or neurobiology in any important way. Relativistic effects, for a human body, would happen on time scales of a couple of nanoseconds. Nothing in sensory processing happens anywhere near that time scale, by orders of magnitude.

 

[dextercioby]

When we read a standard or non-standard textbook on Quantum Mechanics, it's pretty clear what the author's interpretation of the formalism is. But what about General Relativity? More precisely, which interpretation does Robert Wald use in his famous 1984 textbook?

 

[Herman Trivilino]

Like the website looks clean and professional.

It can be really hard for a layman to determine the validity of a professional's website. Perhaps check the validity of the authors in their other writings by checking the references. This may seem like a very difficult task, but it gets a lot easier really fast as you start seeing the same references in related writings.

Note that inherent in this checking process is the reading of multiple authors.

Is this related to the sensory processing delay in the brain? I know the number is like around 0.083 seconds.

It takes light over 4 years to travel from the nearest star to us. That sensory processing time is very much negligible for astronomical objects. Of course it's highly significant when looking at something like your hand because if it's just one inch away (about 2.5 cm) you see it as it was 83 microseconds ago whereas the sensory processing time 83 milliseconds, about 1000 time (3 orders of magnitude) larger.

But then why would special relativity not prove that then? I know there is a delay to our sensation but I would think the math from the theory would supersede that.

I could be wrong about this but it seems you have a fundamental misunderstanding of what theories do for us. We use them to calculate values and make measurements to see how well they compare. If the comparison is off we know the theory is wrong. (Even though it can still be very useful if the comparisons match for a wide variety of situations. In those cases we identify the limits of validity and may choose to use it. Using newtonian theory to navigate to the moon and back is an example).

But if the comparison is a match we know the theory is correct only in that particular case. We make other comparisons and if they match our confidence grows. "Proving" a theory is something that depends on your definition of proof.

 

[Roberto Pavani]

Whether the block universe is truly real is ultimately a metaphysical question.
However, mathematically it is precisely what general relativity delivers:
the Choquet-Bruhat theorem guarantees that well-posed initial data uniquely determine a maximal globally hyperbolic development (a complete four-dimensional spacetime).
In my framework, I adopt this not as a philosophical commitment but as a mathematical constraint, building the theory upon the full block-universe solution of Einstein's field equations.
ORCID: 0009-0002-9098-1203

 

[Dale]

it's highly significant when looking at something like your hand because if it's just one inch away (about 2.5 cm) you see it as it was 83 microseconds ago

I think you mean 83 ps. The speed of light is about 30 cm/ns, so 2.5 cm must be less than a ns.

 

[DaveC426913]

Is this related to the sensory processing delay in the brain? I know the number is like around 0.083 seconds.

Why are we talking about human perception? Relativity worked just fine for the 13.69 billion years before humans came along.

It's a theory of physics, not biology.

Rather than human eyeballs seeing events, think of a passing moonlet being bathed in radiation. Same light-speed delays, same light cones, etc.

 

[Dale]

Why are we talking about human perception?

I always feel that the overemphasis on “observers” can naturally lead to this kind of a misunderstanding.

 

[PeterDonis]

Like the website looks clean and professional.

Then I would recommend adopting a much tighter definition, something more like what I described (you want to be looking at textbooks and peer-reviewed papers, or at least something that's referencing them and trying to explain to you what they say), at least for the purpose of trying to decide whether whatever scientific claims are made are worth your time to consider.

 

[PeterDonis]

Is this related to the sensory processing delay in the brain?

No. It's the time it takes light to travel from whatever emitted it, to you.

 

[Ibix]

When we read a standard or non-standard textbook on Quantum Mechanics, it's pretty clear what the author's interpretation of the formalism is. But what about General Relativity? More precisely, which interpretation does Robert Wald use in his famous 1984 textbook?

As far as I recall he refers to spacetime as a manifold, so he seems to me to be implying a block universe (although you could certainly make a case for him subscribing to shut-up-and-calculate). I think a Lorentz Ether Theory subscriber, for example, ought not to refer to spacetime at all, since only "now" exists in that interpretation.

 

[sbrothy]

The block universe is a specific interpretation of the theory of relativity. Like all interpretations, it makes no experimental predictions different from the theory. The theory of relativity can be experimentally verified or falsified. But all of the interpretations (including block universe) stand or fall together with the theory.

That said, the block universe is the most popular interpretation of relativity. It works well for both special and general relativity. But if you don’t like it then you are not forced to use it by either experiment or theory.

I naively thought that only quantum mechanics "needed" interpretations. You're saying that Relativity can be interpreted in different ways too? How many? Hopefully not as many as QM?

sbrothy starts searching for his Ibuprofen...

 

[PeterDonis]

As far as I recall he refers to spacetime as a manifold, so he seems to me to be implying a block universe

Referring to spacetime as a manifold in the model is not the same as claiming that the entirety of that manifold actually exists in reality as a block universe. The latter is what the "block universe interpretation" is claiming, but that claim is not justified by the former. Modeling spacetime as a manifold is the mathematical framework that GR uses. But the model is not reality.

 

[Herman Trivilino]

I think you mean 83 ps. The speed of light is about 30 cm/ns, so 2.5 cm must be less than a ns.

Oops. I had to go back and edit that post about 3 times because I kept making mistakes. Too early in the morning maybe? Oh well, what's 6 orders of magnitude among friends?

 

[DarkloidNeos]

Then I would recommend adopting a much tighter definition, something more like what I described (you want to be looking at textbooks and peer-reviewed papers, or at least something that's referencing them and trying to explain to you what they say), at least for the purpose of trying to decide whether whatever scientific claims are made are worth your time to consider.

My problem is that I generally cannot understand peer reviewed papers. Physics is my weakest subject and I barely passed the base level, so I rely on articles like the above to understand it. Though I see that's a mistake.

Whether the block universe is truly real is ultimately a metaphysical question.
However, mathematically it is precisely what general relativity delivers:
the Choquet-Bruhat theorem guarantees that well-posed initial data uniquely determine a maximal globally hyperbolic development (a complete four-dimensional spacetime).
In my framework, I adopt this not as a philosophical commitment but as a mathematical constraint, building the theory upon the full block-universe solution of Einstein's field equations.
ORCID: 0009-0002-9098-1203

I'm not sure who is in the right here, because I'm getting different replies. But in this case why would the math not prove it and it would just remain a metaphysical question?

 

[PeterDonis]

My problem is that I generally cannot understand peer reviewed papers.

They are generally written for other physicists, yes. Textbooks offer something somewhat in between, but unfortunately textbooks don't always cover everything.

 

[PeterDonis]

in this case why would the math not prove it and it would just remain a metaphysical question?

See my post #23 about the difference between model and reality.

The math is a model. You can never prove anything about reality with a model. That's why claims like the block universe interpretation--that the entire 4D spacetime manifold is "real", not just a model--are metaphysical questions and can't be proven by math.

You can use a model to make predictions, and compare the predictions with the actual data, and see how accurate the model is. But of course you can only do that for data you actually have--which means you can only make claims about "reality" for the data you actually have. Nobody has data now about what's going to happen a week from now. And whatever any math model says about what's going to happen a week from now is a prediction that we have no way of testing now. So nobody can base any claims about "reality" now on what the model says about what will happen a week from now.

 

[Dale]

You're saying that Relativity can be interpreted in different ways too? How many?

I am sure that there are more than this, but the two main interpretations of relativity are the block universe and the Lorentz aether.

 

[Dale]

I'm not sure who is in the right here, because I'm getting different replies.

I haven’t seen any different replies. They have been remarkably consistent.

Can you point out what replies you thought were in disagreement?

the implications of it are what concern me

It would be useful to know which implications concern you. It may be something “optional” that you can just dismiss if you don’t like it.

But in this case why would the math not prove it and it would just remain a metaphysical question?

Math doesn’t prove things in physics. Experiments do. The issue is that you can always rewrite the math to make the same experimental predictions in different ways. So you can always take the same experimental evidence as supporting different math. This is the fundamental root of why we have different interpretations.

 

[Herman Trivilino]

But in this case why would the math not prove it and it would just remain a metaphysical question?

There is no math in the interpretation! All the math is in the theory. An interpretation is just the way you think about the math when you're doing it.