Undergrad Is Time Just a Stubborn Illusion in the Block Universe Theory?

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• Attempts to promote or resuscitate theories that have been discredited or superseded (e.g. Lorentz ether theory); this does not exclude discussion of those theories in a purely historical context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

 

[Ebeb]

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.

You call LET a "major philosophical interpretation", instead of a "theory"? But the forum rule correctly stipultates it's a theory (see forum quote below) . And LET means ... Lorenz Ether Theory, not Lorentz Ether philosophy.

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.
(my Bold)

If LET is a philosophical interpretation but not a theory, then why calling it a theory?

Just my personal view on this issue.
LET gives another explanation for the phenomena than SR does. That makes it a different theory. LET uses ether, SR not.
If LET is only a philosophical interpretation and no theory, then I would call SR also only interpretation, both being a different interpretation of the Lorentz Transformations: LET interprets with ether, SR without.

Thinking about it LET as interpretation of SR, can we turn it around and call SR an interpretation of LET ? (Never thought physics it can be that much fun;-)

Anyway, don't worry, I won't dig any further into this.

 

[PeterDonis]

If LET is a philosophical interpretation but not a theory, then why calling it a theory?

You're getting hung up on words instead of looking at the substance. The point is that LET and block universe both make all of the same predictions for all experimental results.

I would call SR also only interpretation

"SR" as we are using the term here means the mathematical machinery that makes the predictions, and that's it. No "explanations" beyond that. LET and block universe are two different "explanations" (in your sense of the term) of why that mathematical machinery works. But both use exactly the same mathematical machinery and so make exactly the same predictions.

 

[jbriggs444]

You call LET a "major philosophical interpretation", instead of a "theory"? But the forum rule correctly stipultates it's a theory (see forum quote below) . And LET means ... Lorenz Ether Theory, not Lorentz Ether philosophy.

The Bard:

What's in a name? that which we call a rose. By any other name would smell as sweet

 

[Dale]

If LET is a philosophical interpretation but not a theory, then why calling it a theory?

It is a name that has stuck for historical reasons. It is not a separate theory in the modern usage, but that usage was not fixed at the time it was named.

If LET is only a philosophical interpretation and no theory, then I would call SR also only interpretation, both being a different interpretation of the Lorentz Transformations:

I am fine with that. I assume that in your usage "SR" is synonymous with the "Block Universe". So I think you are saying the same thing I am, but using different words. I don't know that there is an official standard usage.

LET gives another explanation for the phenomena than SR does. That makes it a different theory.

The explanation doesn't define a theory, the experimentally measurable predictions do. Or, at a minimum, the explanation is not physical, which is what most interests me.

 

[SlowThinker]

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).
...
This is the block universe.

You start with the assumption that the future is fixed now, and conclude that the future is fixed now.
Anyway, even if it was, the radioactive atoms still were free to decide when they want to decay, and the photons in double slit experiment were free to decide where they want to land, when the block universe was being built. These decisions might as well be happening only "now" as our consciousness reaches them.

 

[PAllen]

You start with the assumption that the future is fixed now, and conclude that the future is fixed now.
Anyway, even if it was, the radioactive atoms still were free to decide when they want to decay, and the photons in double slit experiment were free to decide where they want to land, when the block universe was being built. These decisions might as well be happening only "now" as our consciousness reaches them.

Ibix is not making any attempt to derive or justify the BU interpretation (over any other), he is just trying to describe it clearly.

 

[Ibix]

You start with the assumption that the future is fixed now, and conclude that the future is fixed now.

As @PAllen says, I'm not justifying the model, merely describing it and setting out why "now" doesn’t fit into it well. The whole point is that there isn't any reason to prefer one interpretation over another except convenience for any given application.

An analogous description of the Lorentz ether theory would be a tablet, possibly with a curved screen, displaying an animated picture of the universe at one time (a series of screen captures could be used to build up the block universe model as I described in the post you quoted). In this model there is a now, but it turns out to be undetectable. Perhaps the best way to explain that is to point out that there are an infinite number of possible tablets with the same shape of screen and, for each choice of screen shape, an infinite number of choices of origin and orientation. So "the" Lorentz ether theory is a bit of a misnomer - there are actually an infinite set of experimentally indistinguishable Lorentz ether theories. So "now" only means something if you adopt one particular Lorentz ether theory - which is a choice on top of choosing Lorentz ether theory, just as it is a choice on top of choosing the block universe.

These decisions might as well be happening only "now" as our consciousness reaches them.

It's worth noting that you don't reach the vast majority of the universe. You are only a tiny little worldline lost in the vastness of space (by any choice of space). So you have to ask: which "now"? And you can't answer by experiment, not even in principle, which is why you can choose either interpretation.

 

[Ebeb]

I am fine with that.

I start feeling better now.

I assume that in your usage "SR" is synonymous with the "Block Universe".

Not necessarily. In that quote I said <<... , both being a different interpretation of the Lorentz Transformations: LET interprets with ether, SR without.>>
In that quote, whether SR means BU is irrelevant. Yes I'm nitpicking here, but let me phrase it differently:
If you start f.ex. with different postulates for explaining phenomena -whether you use different mathematical formulae or not is irrelevant- , then you have a different theory, or not?
But If we get agreement calling SR and LET both "philosophical interpretation" of the LT, I'll settle with that. But it actually means from now on I don't have to call SR a "theory". I'll have to get used to that. ;-)

So I think you are saying the same thing I am, but using different words. I don't know that there is an official standard usage.

You say you "don't know"... I would appreciate you get back to me when you do know whether there is a difference between theory and philosophical interpretation. Just to make sure for future reference on PF discussions.

The explanation doesn't define a theory, the experimentally measurable predictions do.

Well, I'm not so sure about this. It's not what I learned at school.

Or, at a minimum, the explanation is not physical, which is what most interests me.

What interests me is whether they are theories or not. Because, it's important for usagage of specific words on PF forum. And understanding what that PF rule about theories exactly means. I think all participants would appreciate.

Back to BlockUniverse now.
Suppose one day we develop a set of specific BU mathematical formulae (other than LT), producing same experimental (prediction) results as SR or LET does. Would you call it a different theory than SR?

 

[Ebeb]

About 4D terminology.
I still have to sort out a lot more about terminology used -or allowed to use (?)- on PF.
I still don't have a clear view on how the term 4D object is used here.
4D object means we consider the object as one thing, a block. Block Universe (BU) is a 4D object.
Hence, when one would say that SR uses 4D objects/units -I agree-, but refute BU, then I'm lost. Completely lost.

I get the impression that on this forum "spacetime" is considered to be 4D, but not a 4D unit/object/block as a whole?
If spacetime is not 4D unit/object/block, then Newton 'space and time' is also called 4D.
"4D object", will then be used as -I agree- a block, hence BU is a block where past, present and future exist.
Can we stick to this?
I'll then read through the last pages of that other thread (Proper (and coordinate) times re the Twin paradox) and see whether it helps me to understand better the post content.

You have to understand that if you now would get back to me telling there are different 'interpretations' of what 4D means, -so be it- then I need specific guidelines how to differentiate between them, so that all participants understand what is being said in the posts. Because It would be sad such a "miscommunication" issue -and I guess that happens a lot on fora- would be interpreted as not following the PF rules. That's also why I wanted to know whether PF rules considers LET being a theory or not (see above).

 

[SlowThinker]

It's worth noting that you don't reach the vast majority of the universe. You are only a tiny little worldline lost in the vastness of space (by any choice of space). So you have to ask: which "now"?

The events could be happening once their past light cone has been built. I don't think you need some global definition of "now" for that.
Is this what you were trying to picture with those curved tablet screens?

 

[Ibix]

The events could be happening once their past light cone has been built. I don't think you need some global definition of "now" for that.
Is this what you were trying to picture with those curved tablet screens?

I've no idea what you mean here. Lorentz ether theory means that there is a global now, but it's undetectable. It can certainly be any now corresponding to a global inertial frame, but I don't believe it has to be an inertial frame. A non-inertial spatial slice is curved, but it's still a "global now".

 

[Boing3000]

Draw a picture of the universe as it is now on a piece of paper.

It is by far the best way of picturing things, but to fix the misconception about the future being fixed, I prefer to see it the following way:

The stack of "now" should be pictured as a pyramid/cone whose tip/circumference will be imprinted by a local 3D/picture snapshot of the universe (actually the light signals there and then). Then cone grows with time because each circumference 'slice' is your past whose own volume growth at light speed to meet other past.

I may have missed it on this thread, but isn't a 4D map of spacetime entirely frame dependent ? Only those portion of different past cones that intersects (causally linked) will be reconciled by special relativity.

 

[jbriggs444]

I may have missed it on this thread, but isn't a 4D map of spacetime entirely frame dependent ? Only those portion of different past cones that intersects (causally linked) will be reconciled by special relativity.

4D spacetime is entirely frame independent. Special relativity only allows causal influences within light cones. Light cones are not frame dependent.

The coordinate chart(s) that you lay onto the 4D spacetime can vary. And in this sense, yes, a 4D "map" is frame dependent. But none of the physics depends on the map that is chosen. All the physics is frame independent.

 

[PeterDonis]

If you start f.ex. with different postulates for explaining phenomena -whether you use different mathematical formulae or not is irrelevant- , then you have a different theory, or not?

This is a question about words, not about physics.

I get the impression that on this forum "spacetime" is considered to be 4D, but not a 4D unit/object/block as a whole?

The term "spacetime" generally refers to a model using a 4D locally Lorentzian manifold. The model might cover the entire history of a universe, past and future, or it might not--it might only cover a local region (for example, near the Earth during an experiment that has already been run). It depends on the specific scenario being considered.

it's important for usagage of specific words on PF forum.

What's important isn't words, it's physics. As long as you are clear about what physical model your words refer to, that's fine. But you should not be getting hung up on words; the physical models and the predictions they make are what's important.

I need specific guidelines how to differentiate between them

Why? They all use the same model--the same mathematical machinery--and make the same predictions. The model and the predictions are what's important. See above.

That's also why I wanted to know whether PF rules considers LET being a theory or not (see above).

It depends on what you mean by the word "theory". But once again, don't get hung up on words. What we're trying to do here at PF is to focus on the physics--models and the predictions they make. If you find yourself wanting to talk about two thingies that seem different to you, but both use the same mathematical model and make the same predictions, then you should take a step back and reconsider, because whatever differences you see are not differences in the physics.

 

[Boing3000]

4D spacetime is entirely frame independent. Special relativity only allows causal influences within light cones. Light cones are not frame dependent.

The coordinate chart(s) that you lay onto the 4D spacetime can vary. And in this sense, yes, a 4D "map" is frame dependent. But none of the physics depends on the map that is chosen. All the physics is frame independent.

I clearly specified map in my first sentence. Collection of events may be another. The problem is those map are collections of quadruplet of numbers, and all those number are entirely frame dependent.

I never implied the universe is frame depended. I implied clearly that map are frame depended, and the only thing that special relativity allows you is to compare those patch of DIFFERENT map/block that intersects. Only then you always obverse that those map represent the same exact "fix/block" events (once both numbers have been transformed using SR formulas).

I find this way of picturing things much more sane than to speak of future light cone that exist nowhere in any frame of reference. There is a past block universe, only accessible trough patch of individual frame dependent block map.

The "absolute" 4D spacetime (if such a thing exist) is nowhere to be observed directly. But I do agree it is independent. It is so independent that there are patch of it/them that are not even connected (if the expansion of the universe keeps accelerating).

 

[jbriggs444]

I find this way of picturing things much more sane than to speak of future light cone that exist nowhere in any frame of reference.

What makes you say that the future light cone does not exist in any frame of reference?

 

[tophatphysicist]

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.

So, your point is that by not accepting the Block Universe, it is not that this one concept is not accepted as uniquely unconfirmed, rather it is not accepted along with all physical laws and theories not accepted (because nothing can be confirmed that is outside the light cone). For the longest time I was assuming that Block Universe was being uniquely identified by the Physics Forum as a major concept that has been falsely presented as a validated concept. I think it might have a different impact on visitors to the Forum to understand the absence of validation is in the context of the more general principal that there can be no proof of theories (or predictions) regarding events outside of the light cone.

Regarding Block Universe specifically, then, notwithstanding the understanding that Block Universe applies to universe past, present and future, is it accepted that the relativity of simultaneity leads to the concept that space is 4-dimensional and fixed within the past light cone -- and that this conclusion is accepted as valid by the Physics Forum and physics community at large?

 

[PeterDonis]

So, your point is that by not accepting the Block Universe, it is not that this one concept is not accepted as uniquely unconfirmed, rather it is not accepted along with all physical laws and theories not accepted (because nothing can be confirmed that is outside the light cone).

No. I didn't say we couldn't accept that the laws of physics apply outside our past light cone. I just said we couldn't confirm this, since the only way to confirm it would be by collecting evidence, and we can't collect evidence outside our past light cone.

You also seem to be ignoring the fact that "our past light cone" is not a fixed region of spacetime. It grows as we move into the future along our worldline. So even if we can't confirm today that the laws of physics apply in the region of spacetime that is currently outside our past light cone, tomorrow we will be able to confirm it for some portion of that region (the region that is less than one light-day outside our past light cone today).

For the longest time I was assuming that Block Universe was being uniquely identified by the Physics Forum as a major concept that has been falsely presented as a validated concept.

Go back and read my article. I did not say anywhere in that article that the Block Universe was false. I just said that one particular argument that was presented about it was not a valid argument. That's all I said.

is it accepted that the relativity of simultaneity leads to the concept that space is 4-dimensional and fixed within the past light cone

No, because you don't need relativity of simultaneity in order to know that events in your past light cone are fixed and certain. You can observe those events directly without having to know anything about simultaneity at all.

You really need to stop inserting your own preconceptions into what you read.

 

[Ebeb]

... that events in your past light cone are fixed and certain. You can observe those events directly ... .

No, you cannot observe them directly. You observe them after they occurred.

You also seem to be ignoring the fact that "our past light cone" is not a fixed region of spacetime. It grows as we move into the future along our worldline. So even if we can't confirm today that the laws of physics apply in the region of spacetime that is currently outside our past light cone, tomorrow we will be able to confirm it for some portion of that region (the region that is less than one light-day outside our past light cone today).

Does the above confirms that you accept there are events outside the lightcone before they enter into the light cone as observer's time progresses?
Because striclty speaking one doesn't know whether there are events outside the lightcone. Correct? And one -strictly speaking- doesn't know that when you do observe an event, that that event was/existed/occurred outside the lightcone before it is observed.
Does this mean that - and I guess this is what Tophatphysicist is getting at- that special relativity can not necessarily be applied to that zone?
Hence all the simultaneity planes through the apex of lightcone pictures on the internet are wishfull thinking?
Still trying to understand you.

 

[Boing3000]

What makes you say that the future light cone does not exist in any frame of reference?

Projection don't exist, hence the name. The future does not exist, it will eventually. The past ends at the present. That does not preclude us to use projection/prediction,but they are entirely based on the past.

Another way of saying that is I (a particle with rest mass (but no gravitas obviously )) am certainly never going to catch up/intersect with any light cone emitted at any time from my past to "observed" its existence. But other will, mostly mirrors...

I think it is a pretty straightforward definition of the growing block universe

 

[PeterDonis]

You observe them after they occurred.

Yes, which means that when you observe them, they are in your past light cone. That is what I meant by "observe them directly"--you get light signals direct from the events. You don't have to make any calculations or do any extrapolation or prediction.

Does the above confirms that you accept there are events outside the lightcone before they enter into the light cone as observer's time progresses?

No.

Because striclty speaking one doesn't know whether there are events outside the lightcone. Correct?

No, because you haven't observed them yet.

And one -strictly speaking- doesn't know that when you do observe an event, that that event was/existed/occurred outside the lightcone before it is observed.

More precisely, you have no way of testing by experiment whether or not the event "existed" before you observed it--because any experiment would involve observation.

Does this mean that - and I guess this is what Tophatphysicist is getting at- that special relativity can not necessarily be applied to that zone?

No, because SR is a model. You can make a model of (hypothetical) events that you haven't observed yet. But the model is not reality. You can't make claims about the events being "real" based on the model. The model is a tool for prediction, not for telling you what's "real".

 

[Dale]

If you start f.ex. with different postulates for explaining phenomena -whether you use different mathematical formulae or not is irrelevant- , then you have a different theory, or not?

That isn't the way I would categorize different theories, but at least it is clear and I can understand what you are saying. You are saying that a theory is defined by its postulates or axioms, I am saying that it is defined by its experimental predictions. I think your usage is non standard, but I don't have an official definition either way.

I would appreciate you get back to me when you do know whether there is a difference between theory and philosophical interpretation

I do know that I (and many of the forum regulars) use the terms as I have described. I do not know if there is an official authoritative source where those terms have been defined. That is why I have made my usage explicit and asked you to do the same.

Suppose one day we develop a set of specific BU mathematical formulae (other than LT), producing same experimental (prediction) results as SR or LET does. Would you call it a different theory than SR?

Based on what I have previously stated defines a theory what do you think I would say?

Hence, when one would say that SR uses 4D objects/units -I agree-, but refute BU, then I'm lost. Completely lost.

Who refuted BU? I certainly did not. I wouldn't even attempt to refute any interpretation. A refusal to accept is not the same as a refutation.

 

[Dale]

So, your point is that by not accepting the Block Universe, it is not that this one concept is not accepted as uniquely unconfirmed, rather it is not accepted along with all physical laws and theories not accepted (because nothing can be confirmed that is outside the light cone).

That is not my point. My point is that the Block Universe is an interpretation, not a theory. As an interpretation it makes no physical predictions that distinguish it from other interpretations.

I accept or reject physical laws and theories on the basis of their experimental predictions. Interpretations (including the Block Universe) make no new predictions, so they do not need to be accepted or rejected.

 

[Ebeb]

Who refuted BU? I certainly did not. I wouldn't even attempt to refute any interpretation. A refusal to accept is not the same as a refutation.

It's not about what my post is about. I'll try again:
You were very clear in that other thread that -your quotes (from this post)- <<Clocks are 4D objects.>><<Measuring sticks are 4D objects.>>
I still don't understand what you mean by 4D objects. Because: 4D objects means: the full worldline. Past present and future in one unit. Block Universe is a 4D object.
Measuring a 4D object is: measuring the 4D block. If SR deals with 4D objects, then SR is about Block Universe. How can SR not be about Block universe if you tell me clocks and measuring sticks are 4D objects? That is what I still don't understand and what I tried to communicate in my post.

Just curious; would you say that in LET the clocks and measuring sticks are also 4D objects?

 

[jbriggs444]

Projection don't exist, hence the name.

The word projection does not appear in the phrase "frame of reference". If you want to restrict a frame of reference to your past light cone that seriously limits your ability to use that frame of reference to make any predictions.