Is Time an Illusion? Exploring the Block Universe Theory

[tophatphysicist]

Einstein said, "The distinction between past, present and future is only an illusion, even if a stubborn one."

That's my problem--that illusion is so vivid and stubborn.

Paul Davies said in his book "About Time": There is only one rational conclusion to draw from the relative nature of simultaneity; events in the past and future have to be every bit as real as events in the present.

 

[jbriggs444]

Paul Davies said in his book "About Time": There is only one rational conclusion to draw from the relative nature of simultaneity; events in the past and future have to be every bit as real as events in the present.

If you decide that by the force of pure reason you can tell how things must be, that is a clue that you have departed from science into philosophy.

 

[tophatphysicist]

If you decide that by the force of pure reason you can tell how things must be, that is a clue that you have departed from science into philosophy.

But, he didn't decide just by the force of pure reason. He decided based on measurements and observations culminating in the relative nature of simultaneity.

I like your comments, jbriggs444. And your avatar is by far my favorite on the forum.

 

[PeterDonis]

Paul Davies said in his book "About Time": There is only one rational conclusion to draw from the relative nature of simultaneity; events in the past and future have to be every bit as real as events in the present.

This is a common unjustified claim in pop science books. Read this Insights article:

https://www.physicsforums.com/insights/block-universe-refuting-common-argument/

 

[tophatphysicist]

This is a common unjustified claim in pop science books. Read this Insights article:

https://www.physicsforums.com/insights/block-universe-refuting-common-argument/

Peter, does an expert such as Einstein, Roger Penrose or Paul Davies lose his stature and authority in physics as soon as he writes a book for the general public? Or, maybe you're suggesting that he alters the true description of the physics for public consumption? I was quite impressed with Roger Penrose's book (also read it years ago). I still look forward to reading your article. Thanks for your contributions to the forum.

 

[Ebeb]

Peter, does an expert such as Einstein, Roger Penrose or Paul Davies lose his stature and authority in physics as soon as he writes a book for the general public? Or, maybe you're suggesting that he alters the true description of the physics for public consumption? I was quite impressed with Roger Penrose's book (also read it years ago). I still look forward to reading your article. Thanks for your contributions to the forum.

I found this interesting quote about Einstein and block universe:
Karl Popper about Einstein:
<< The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. (He agreed that this had been his view, and while discussing it I called him "Parmenides".)... >> (Karl Popper, Unended Quest: An Intellectual Autobiography.Routledge Classics. Routledge. pp.148–150).

 

[PeterDonis]

does an expert such as Einstein, Roger Penrose or Paul Davies lose his stature and authority in physics as soon as he writes a book for the general public?

No, because they never had any in the first place in the sense you mean. Science does not work on "stature and authority". Nobody should be believed or their arguments accepted without examination simply because they are a famous physicist. That goes just as much for their peer-reviewed science as for their pop science. Even famous physicists sometimes get things wrong, so you have to check what they say. That was part of the reason I wrote that Insights article--to show that even someone as smart as Roger Penrose can make mistakes.

maybe you're suggesting that he alters the true description of the physics for public consumption?

I don't think that's the case with the particular argument I refuted in the Insights article. I think it was an honest mistake. But an honest mistake is still a mistake.

I do think a lot of pop science books leave things out, and the authors aren't always very careful to say what they are leaving out, or why, or how it affects what they keep in. Feynman, in one of his pop science books (I think it was QED, but I'm not sure), at least said that he was being careful to mention all the stuff he was leaving out (and did a pretty good job of keeping that promise). But many, if not most, authors aren't as careful as that.

 

[Ebeb]

This is a common unjustified claim in pop science books. Read this Insights article:

https://www.physicsforums.com/insights/block-universe-refuting-common-argument/

Peter, I gave it another go. Correct me if I'm wrong, but you don't seem to accept that special relativity is about 4D objects and 4D universe. In previous posts in this thread I agreed with Dale , JBriggs ... that special relativity is all about 4D objects and 4D universe. 4D means units that include past, present and future. And I found it very interesting and agreed with them that "3D section" (3D world of simultaneous events) should be replaced by 4D slice out of the full 4D object/universe.

Obviously, if you don't accept special relativity is about 4D objects/4D universe, then you can never understand, nor accept Block Universe, nor slices through 4D Block Universe... Is this what I read in your article?

 

[jbriggs444]

And I found it very interesting and agreed with them that "3D section" (3D world of simultaneous events) should be replaced by 4D slice out of the full 4D object/universe.

Please do not put words into our collective mouths.

 

[Dale]

@Ebeb note that I do not "accept Block Universe". I use the Block Universe interpretation when it suits my needs and I use LET instead when it suits my needs. I don't accept or reject either.

Instead, I pay attention to which parts of each interpretation are physical (experimentally measurable) and which parts are philosophical. I use the most convenient philosophical tools as needed, but work hard to keep the experimentally measurable stuff in the forefront. I am not 100% successful, but I work at it.

 

[PeterDonis]

Correct me if I'm wrong, but you don't seem to accept that special relativity is about 4D objects and 4D universe.

I made no such general statement in the article; I specifically said that I was only refuting one particular argument, the argument that relativity of simultaneity implies that the 4D "block universe" model must be true.

Is this what I read in your article?

No. See above.

 

[Dale]

I have no problem calling the universe an object and therefore it is physically 4D. Certainly, it has been measured to have nonzero extension in the time dimension.

However, the Block Universe goes further and asserts that the future is also fixed. I have no physical measurements that support that claim. I don't object to it, but in the absence of measurements of the future, it is in my "not physical" category.

 

[Ebeb]

I have no problem calling the universe an object and therefore it is physically 4D. Certainly, it has been measured to have nonzero extension in the time dimension.

However, the Block Universe goes further and asserts that the future is also fixed. I have no physical measurements that support that claim. I don't object to it, but in the absence of measurements of the future, it is in my "not physical" category.

Allow me to try once more understand what you guys have in mind.

Do you have physical measurement that a present world exists?
You cannot measure a present world, because 'present world' is based on simultaneity, and because simultaneity is a mathematical relative thing, you have to consider 'present world' non-existent. This means there is nothing existing 'now' at a distance from an observer. And because you don't accept the full life of a remote object exists out there, there is simply nothing out there to be observed/measured.
Only the present 'now' event of an observer does definitely 'exist now' for him.
This is even more confusing, because you would definitely reject we are solipsists.
Yes, I guess you will find the above a total mess, but the posts I read in this thread won't help either.
It's sad, but there seems to be no way we can or will understand each other... Very weird because for decades now I do understand perfectly what Einstein, Penrose, Davies, ... tell me in their writings. But that too I got wrong, isn't it?

 

[PeterDonis]

Do you have physical measurement that a present world exists?

No. Our physical measurements can only tell us about our past light cone. We don't physically measure 3-D worlds. (This is all discussed in my Insights article.)

 

[PeterDonis]

This is even more confusing, because you would definitely reject we are solipsists

That's right--because our direct observations tell us that all the events in our past light cone exist, so what exists is certainly not limited to our present moment, i.e., to a single event. And those events in the past light cone include all kinds of evidence of the existence of objects other than ourselves. (This is also discussed in my Insights article.)

 

[PAllen]

Allow me to try once more understand what you guys have in mind.

Do you have physical measurement that a present world exists?
You cannot measure a present world, because 'present world' is based on simultaneity, and because simultaneity is a mathematical relative thing, you have to consider 'present world' non-existent. This means there is nothing existing 'now' at a distance from an observer. And because you don't accept the full life of a remote object exists out there, there is simply nothing out there to be observed/measured.
Only the present 'now' event of an observer does definitely 'exist now' for him.
This is even more confusing, because you would definitely reject we are solipsists.
Yes, I guess you will find the above a total mess, but the posts I read in this thread won't help either.
It's sad, but there seems to be no way we can or will understand each other... Very weird because for decades now I do understand perfectly what Einstein, Penrose, Davies, ... tell me in their writings. But that too I got wrong, isn't it?

There are things far away from me that I detect from my past light cone. I readily infer their history continues beyond my last observation. However, which point in such unobserved future of the object corresponds to my present moment is not part of physics, it is the composition of convention and extrapolation. Even in my past light cone, the correspondence between events in the distant object's history and events in my past is a matter of convention, not physics. Even in SR, there is more than one convention in common use, while in GR, one hardly even bothers with the notion of distant now because of the plethora of choices with no basis for preferring any.

 

[tophatphysicist]

PeterDonis, just trying to make sure I understand the Premise 2 that you are concerned about in your article on Block Universe. Is it that the Block Universe should not be accepted because it has not been verified with observations not available within our light cones? Should it be accepted if events outside of our light cone could demonstrate the same conclusions as presented by Penrose in his paradox?

 

[PeterDonis]

Is it that the Block Universe should not be accepted because it has not been verified with observations not available within our light cones?

My argument is not that the block universe "should not be accepted". It is that the specific argument I described in the article is incorrect, because its second premise is not required by SR.

if events outside of our light cone could demonstrate

It is impossible for us to have knowledge of events outside our past light cone, so this suggestion is meaningless.

 

[tophatphysicist]

It is that the specific argument I described in the article is incorrect, because its second premise is not required by SR.

Sorry to belabor the point, but what do you mean by "...its second premise is not required by SR"? Do you mean that SR does not require relativity of simultaneity for events outside of our light cones, therefore the Block Universe theory is also not required by SR outside of our light cones? Would you then be saying that SR theory is not validated for events outside of our light cones?

 

[PeterDonis]

what do you mean by "...its second premise is not required by SR"?

The second premise is "3D worlds are real at every event". That premise is not required by SR.

Would you then be saying that SR theory is not validated for events outside of our light cones?

How can it be, since, as I said before, it is impossible for us to have knowledge of events outside our past light cone?

 

[tophatphysicist]

How can it be, since, as I said before, it is impossible for us to have knowledge of events outside our past light cone?

O.K. I think I see your position -- a fundamental tenet of operationalism. This is the concept that none of the laws of physics can be known to apply in the future (outside of our past light cones). I had not anticipated that the Physics Forums would operate from that stance. You can certainly make the point that this would certainly be the case particularly for the 4-D object universe. Particularly, since the Block Universe discards causality, so that now the orientation of future segments of the 4-D fiber bundles are not constrained to follow patterns dictated by causal events involving forces, etc. In that sense they are ever free to take arbitrary paths, without the laws of physics to order their configurations. Sometimes operationalism gets us wandering too far into philosophy. I don't think most physicists work within that kind of context.

We amass data from the past light cone and infer future conformance of test results to past results.

 

[PeterDonis]

This is the concept that none of the laws of physics can be known to apply in the future (outside of our past light cones).

I didn't say anything about the laws of physics. I said it is impossible for us to have knowledge of events outside our past light cone. As far as the laws of physics, that means that we can't confirm by evidence that the laws of physics apply outside our past light cone. But it says nothing at all about our ability to use the laws of physics to predict events that we have not yet observed--which is, of course, what we do with them all the time. We just have to bear in mind that those are predictions, and that there is a difference between predictions and actual observations.

the Block Universe discards causality,

It does no such thing. The block universe is perfectly consistent with SR, which is a causal theory.

the orientation of future segments of the 4-D fiber bundles are not constrained to follow patterns dictated by causal events involving forces

I have no idea where you are getting this from.

Sometimes operationalism gets us wandering too far into philosophy.

It seems to me that you are wandering too far away from actual physics.

We amass data from the past light cone and infer future conformance of test results to past results.

Yes, we infer. Inferring is not the same as observing. Once we observe that a prediction was confirmed, the events that confirmed the prediction are in our past light cone.

 

[Ebeb]

The second premise is "3D worlds are real at every event".

That cannot be the premise, because "3D worlds are real at every event" is the conclusion: block universe.The premise you probably introduce and refute is: "a 3D world is real at an event". Correct? I.o.w. you don't accept simultaneity of events in the spacelike/elsewhere zone? In that case let me first make sure what you precisely mean. Do you only refute simultaneity in the spacelike/elsewhere zone, but still accept there are/occurring/existing events in your spacelike/elsewere zone? Or are you saying that at the apex you don't know anything about spacelike/elsewhere zone, hence there are no events at tall occurring/existing in that zone?

 

[PeterDonis]

That cannot be the premise, because "3D worlds are real at every event" is the conclusion: block universe.

The block universe conclusion is not "3D worlds are real at every event". It is "all of 4D spacetime is fixed and certain". That's the claim that is being argued for in the argument I refute in the article. The claim "3D worlds are real at every event" translates to "at any given event, all 3D worlds that contain that event are fixed and certain".

The claim about 3D worlds certainly implies the block universe claim: I discuss that in the article. But that doesn't make it the same claim.

 

[PeterDonis]

let me first make sure what you precisely mean.

None of your attempts capture what I meant. Go back and read the article again, and this time read the actual words I wrote, without filling in anything from your own assumptions.

 

[Ebeb]

None of your attempts capture what I meant. Go back and read the article again, and this time read the actual words I wrote, without filling in anything from your own assumptions.

Seems we cannot even agree what Block Universe means. This is getting hilarious. (I must definitely be an idiot. Let me think about it.)

 

[PeterDonis]

Seems we cannot even agree what Block Universe means.

If you have trouble understanding what I said in the article, go back to the sources I referenced (in particular the Wikipedia article I linked to and the book by Penrose that it quotes from). If you think I'm misstating what they mean, feel free to post here explaining why.

 

[PeterDonis]

Also, for reference, here is the previous discussion on the Insights article:

https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/

 

[Ibix]

Draw a picture of the universe as it is now on a piece of paper. Draw a picture of the universe as it is a second later and stack it on top of the first piece. Draw another picture of the universe another second later and stack it on top of the other two. Repeat until you've drawn the entire future and past of the universe (warning: this may require infinite time). Now find an acid that erodes paper but doesn't touch your ink. Remove the paper, leaving towers of ink that are the 2+1 dimensional history of all the objects in the universe. Smooth out the jags in the towers caused by the original choice of finite time steps..

This is the block universe.

When we pick a reference frame we choose a definition of "time" and hence a definition of "the universe now", and we think of inserting paper into our ink-only model. But there's nothing to tell us how to do that insertion. We could choose any set of planes, not even necessarily flat. And we don't actually insert the paper and there was never any paper to begin with - just the ink. Imagining a stack of paper one sheet at a time is just something we do because that's how our poor monkey brains visualise the universe. And since we're not actually doing anything and there's no reason to prefer one choice of planes over another, we say that "now" isn't a physical thing. We aren't denying that stuff outside our light cone exists, just saying that anything that's a free choice with no effect on the results (like your choice of how to insert the paper, which you can't actually do) can't have physical significance.

 

[Ebeb]

Also, for reference, here is the previous discussion on the Insights article:
https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/

I see I'm in the same boat of the participants of that thread. I'm in fact very glad to see I'm not the only one having trouble understanding your article.

None of your attempts capture what I meant.

O.K. Knowing this helps.

Go back and read the article again, and this time read the actual words I wrote, without filling in anything from your own assumptions.

I'll give it another shot.

 

[Ebeb]

@Ebeb note that I do not "accept Block Universe". I use the Block Universe interpretation when it suits my needs and I use LET instead when it suits my needs. I don't accept or reject either.

Wouln't this be against the forum rules?

Generally, in the forums we do not allow the following:

• Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory); this does not exclude discussion of those theories in a purely historical context

 

[PeterDonis]

Wouln't this be against the forum rules?

Using it as an interpretation for calculational convenience is not the same as claiming it is an actual theory, i.e., that the world "really is" the way LET or the Block Universe says it is. The latter is what is not allowed.

 

[tophatphysicist]

Dale said: ↑
@Ebeb note that I do not "accept Block Universe". I use the Block Universe interpretation when it suits my needs and I use LET instead when it suits my needs. I don't accept or reject either.

Dale, I'm not trying to be contentious here. I'm just trying to get clarification on your basis for not accepting the Block Universe theory. I think I understand your point that even though the block description appears to be valid within your past light cone, it cannot be accepted as valid in the future, since it is not possible to know the future, i.e., not possible to make measurements outside of your light cone. Do I have that part correct?

 

[PeterDonis]

even though the block description appears to be valid within your past light cone

This doesn't make sense. The block universe view is that all of 4D spacetime is fixed and certain, not just the portion within the past light cone of some chosen event.

 

[Dale]

I'm just trying to get clarification on your basis for not accepting the Block Universe theory

The Block universe is not a theory, it is an interpretation. It makes no new experimental predictions. It makes the same prediction for every experimental measurement as LET, the other major philosophical interpretation of SR. So they are physically indistinguishable (again with "physical" meaning "experimentally measurable")

Since nature does not prefer one over the other, I see no need to do so either.

I think I understand your point that even though the block description appears to be valid within your past light cone, it cannot be accepted as valid in the future, since it is not possible to know the future, i.e., not possible to make measurements outside of your light cone. Do I have that part correct?

This is essentially correct, but it is not my motivation. My motivation is that I want to use models that make accurate predictions of experimental measurements. Thus my interest is in whether or not something is "physical".

Interpretations go beyond the experimental predictions and make claims about "reality" and "existence". These sound like science terms, but they are philosophical terms. Specifically, they are from the branch of philosophy called metaphysics.

So I accept or reject theories based on physical evidence compared to the physical predictions. I remain neutral about interpretations, neither accepting nor rejecting them, on principle.

For me, interpretations merely serve as a mental aid to help organize my thoughts as I solve a problem. Different mental organizations may be useful for different problems, so I learn multiple interpretations and use whichever seems convenient for the problem at hand. So for me, the proper way to evaluate an interpretation is useful/useless rather than accept/reject.