I How Does Special Relativity Challenge Our Understanding of Absolute Time?

[name123]

That never happens. Everyone will agree as to what happens to any given observer, though they might disagree as to the timing of some event that led to what that observer experienced.

Thanks again for the diagrams they were really good. I think that the difference disagreements in simultaneity would get smaller the closer the events are, but there would still be differences. So if the person was lying on its back on the train looking up, there could be disagreements about whether two lasers simultaneously hit each of the person's eyes or not (if one was aimed at each. But I am going to stop responding to this thread after this set of posts, because thanks to those on this forum including yourself, the confusions I had have been cleared up, and I think the issues now are slightly philosophical, and so maybe a topic for the general forum or something, but not here. Thanks for the help.

 

[Janus]

Thanks again for the diagrams they were really good. I think that the difference disagreements in simultaneity would get smaller the closer the events are, but there would still be differences. So if the person was lying on its back on the train looking up, there could be disagreements about whether two lasers simultaneously hit each of the person's eyes or not

But no disagreement over what the person would "see". The nerve impulses created by the light hitting the eyes still has to travel to the visual cortex, and whether or these impulses arrive there simultaneously or not would not be in dispute.
Another example would be the person standing with his arms outstretched. The palms on his hands are pricked with a needle. According to his frame, this is done simultaneously, the nerves impulses travel along the arms to his brain and arrive simultaneously. He "feels" the needles poke his hands at the same time. He reacts, sending impulses back down the arms, causing his hands to flinch, again simultaneously.
In another frame, the needle pricks don't occur simultaneously. But the nerve impulses traveling along the arms are subject to the relativistic addition of velocities and so the speed at which they travel with respect to the arms is not equal. And event though one impulse starts before the other, they still both reach the brain at the same time and the person still "feels" the needle pokes at the same time. The reflex impulse leaves the brain at the same moment, but because of the same effect of velocity addition, arrive at each hand at different times causing them to flinch at different times.

 

[name123]

I am going to stop responding after this post, as the forum has helped out on the things I was confused about and the conversation would seem to be getting a bit philosophical now and so off topic. I would be happy to discuss it on another thread in another forum if anyone wanted to continue, but do not want to annoy people on this forum.

It most certainly does not reflect simultaneity of neural events, because it would violate the laws of physics for simultaneity to cause anything. Whatever causes any observable (including experience) must be entirely within some past light cone, not on any surface of simultaneity. This is known as causality.

I was assuming that most physicalists would think that what caused that surface of simultaneity, also caused the experience. That corresponding to the experience was some physical state that had been caused. That the experience was a property of that physical state, and that like other properties of that physical state, they are simultaneous to it.

I am not clear on what you are suggesting here. You seem to be suggesting that the experience will not be a property of some physical event but be something non-physical that is acted upon by physical events and that this acting upon takes time, such that the experience cannot be simultaneous to the physical events that acted upon it. Interesting, but I am not sure any physicalist would go for it, as what would be this entity in the ontology that is acted upon.

Also even with events in the past light cone, there can be a difference in opinion over whether they were simultaneous or not.

It isn’t a slippery slope, it is hard data. For example, if there is a coherent visual and auditory stimulus (e.g. a movie), and if the auditory stimulus is delayed anywhere from 0 to about 100 ms, then the experience is the same. The experience is that there is no discrepancy. So it is a clear experimental fact that different neural states lead to the same experience. Any theory of experience that can not accommodate that is already falsified.

There is a difference between the experience being the same, and not being able to distinguish between the experience. For example consider the experiment you just quoted. The subjects might not be able to distinguish between which of two identical visual presentations had a time delayed audio. But that does not mean the experience is the same. If you were to play the audios together, and one was time delayed by a 100ms then you could clearly hear the difference. So in retrospect you could tell that the experience wasn't actually the same even though you couldn't distinguish which had time delayed audio. And that was my point. Sometimes though you might not even be able to tell the difference between two experiences when they are presented at the same time. Consider an RGB colour on your computer. You could compare two which are only 1 value apart, and you might not be able to distinguish them. That does not mean they are all the same though (though possibly on some the brain would encode them in the same way). You might keep increasing the colour values by 1 and then go back and compare to the original and find that there is quite a difference even though you did not notice it when slowing increasing the value. But like with the auditory, it doesn't mean that they are the same just because you do not notice the difference. Otherwise as I pointed out if you said that e₁ = e₂ and e₂ = e₃ and so on, then you would be saying e₁ = e_n regardless of the value of n, but with the RGB values it is easy to tell that that claim is wrong, and that for some at least there must have been a difference.

One key physical constraint is that spacelike separated events cannot be causally related, so the experience cannot be a function of simultaneous neural states. Of course, given how slowly the experience changes and how small the brain is, this really is a non-issue and you can simply think of the brain as a point object wrt relativity and experience. However, even though it is a non-issue (as I have repeatedly shown) you continue to push it.

Well presumably this is up for debate given "spooky" action at a distance. But ignoring the "spooky" action, and quantum mechanics, presumably all simultaneous finite points are considered to have spacelike separation. And each simultaneous point will have its own past light cone. I don't know whether you are expecting the answer regarding experience to depend on which point was chosen, or whether it would rely on some overlap of past light cones. But then I am not sure what you are thinking what the contents of those past light cones are having an influence on to give rise to experience. As I mentioned it doesn't seem as though you are envisaging it to be something physical.

The point is that whether in a past light cone or not, presumably the relative timing of the relevant events will have an influence on the experience, and while you may not consider the influence to be significant (as the difference in timing could be very small), it does seem to me that there would be a difference, however small. Unless perhaps you were considering the influence to be the influence at some particular point. I was not considering whether it would make any pragmatic difference, only that however small the difference in accounts were by observers, whether there can be multiple true answers to the way it was for you (however close they were), or whether there is only one true answer for how it was.

Anyway, if you want to continue, perhaps let me know and start up a thread in a different forum. If not, then thanks for the help and the time you have taken, I appreciate it, and thanks to the others on the forum that have also helped.

 

[PeterDonis]

I was assuming that most physicalists would think that what caused that surface of simultaneity, also caused the experience.

No, physicalists would say that a surface of simultaneity is not a physical thing to begin with; it's an arbitrary abstraction like a coordinate system. That is the fundamental point that you keep missing in this discussion.

even with events in the past light cone, there can be a difference in opinion over whether they were simultaneous or not.

Yes. So what? Simultaneity is not a physical thing anyway, and can't cause anything or be the effect of anything. It's just an arbitrary human convention.

presumably this is up for debate given "spooky" action at a distance.

No, it isn't. Quantum phenomena still obey relativistic causality.

presumably the relative timing of the relevant events will have an influence on the experience

If by "relative timing" you mean the order in which causal influences from different places arrive at some particular place, yes, of course this will have an influence on experience. But this has nothing to do with simultaneity. The order in which signals arrive from elsewhere at a particular location is a relativistic invariant; it doesn't depend on your choice of coordinates or simultaneity convention.

 

[Ebeb]

No, physicalists would say that a surface of simultaneity is not a physical thing to begin with; it's an arbitrary abstraction like a coordinate system.

The set of simultaneous events I consider occurring 'now' is the 3D world I consider existing 'now'.
If a set of simultaneous events does not represent anything physical, then which 3D world do physicists consider physical?

 

[Dale]

If a set of simultaneous events does not represent anything physical, then which 3D world do physicists consider physical?

No 3D world is physical. The physical world if 4D. Didn’t we have a really really long conversation about this already?

 

[Ibix]

The set of simultaneous events I consider occurring 'now' is the 3D world I consider existing 'now'.
If a set of simultaneous events does not represent anything physical, then which 3D world do physicists consider physical?

The usual model is to treat spacetime as a 4d whole. You can select any 3d plane passing through your worldline "now" and call that "the universe now", but there's no significance to any particular choice. All are arbitrary 3d subsets of the 4d whole.

We're not saying that the 3d subsets don't exist. Just that there are infinitely many ways to pick a subset and no good reason to prefer one choice over another.

 

[PeterDonis]

If a set of simultaneous events does not represent anything physical, then which 3D world do physicists consider physical?

None. As @Dale and @Ibix have said, the usual model is to consider 4D spacetime as "real". An alternative is to consider the events in your past light cone as "real". The latter is the most parsimonious view IMO, since the actual evidence we have is all information in our past light cone.

 

[Dale]

I was assuming that most physicalists would think that what caused that surface of simultaneity, also caused the experience.

A surface of simultaneity isn’t something that is caused, it is merely arbitrary defined. It has no physical significance, neither as a cause nor as an effect.

That corresponding to the experience was some physical state that had been caused. That the experience was a property of that physical state, and that like other properties of that physical state, they are simultaneous to it.

All good until that last phrase.

You seem to be suggesting that the experience will not be a property of some physical event but be something non-physical

I did not suggest any such thing.

The subjects might not be able to distinguish between which of two identical visual presentations had a time delayed audio. But that does not mean the experience is the same.

I disagree. If two stimuli are subjectively indistinguishable then the experience is the same. The experience is not the stimulus, it is the subjective conscious experience that results from the stimulus. So if you cannot consciously distinguish two stimuli then the experience is the same.

Consider an RGB colour on your computer. You could compare two which are only 1 value apart, and you might not be able to distinguish them. That does not mean they are all the same though

Yes, they are not the same, but the conscious subjective experience is the same. You seem to be confounding the stimulus with the experience.

Otherwise as I pointed out if you said that e1 = e2 and e2 = e3 and so on, then you would be saying e1 = en regardless of the value of n,

No. When there is a threshold then at some point a small change makes a subjective difference. So (using what I am guessing your notation means) if e1=e2 that does not imply that e101=e102 even if all of the increments are equally small.

For example, if the numbers represent ms of delay and if the threshold for a given person is exactly 100 ms then subjective experience e0=e95 but e95$\ne$e105, even though the objective stimuli are closer. This is what a threshold response means. Small differences in input near the threshold lead to large differences in the outcome. There is no slippery slope involved, such mathematical functions are perfectly legitimate, although they can be numerically difficult.

Well presumably this is up for debate given "spooky" action at a distance.

No, it isn’t a matter of debate at this point. QFT is fully relativistic and respects causality as described above. In QFT this is enforced by the commutation relationship of spacelike separated events.

The point is that whether in a past light cone or not, presumably the relative timing of the relevant events will have an influence on the experience,

Certainly, but the distinction between the past light cone and the surface of simultaneity is important. If an experience is caused by a surface of simultaneity then it violates all known laws of physics. If experience follows the known laws of physics then it must be caused by the past light cone and, since all reference frames agree on the past light cone then all reference frames would agree on what was experienced (given a perfect theory of experience). The “truth of your experience” would therefore be frame invariant. Which was your question that started rhis whole tangent.

 

[name123]

One key physical constraint is that spacelike separated events cannot be causally related,...

Well presumably this is up for debate given "spooky" action at a distance

No, it isn't. Quantum phenomena still obey relativistic causality.

I wasn't going to respond to the philosophical stuff, but since this is directly to do with physics I will.

Are there not experiments where entangled particles are separated and they then subsequently have certain properties tested such as their spin for example, and that even if they are tested within a time frame which wouldn't allow for any causal effect from the testing of one even if traveling at the speed of light to have influenced the testing of the other, the spins for example are always opposite?

Does Bell's Inequality theorem not indicate that there could be no local hidden variables responsible?

Obviously the issue isn't whether the experiment proves there is spooky action at a distance (there is Everett's theory for example), just whether a case can be put forward for there being such spooky action.

 

[A.T.]

...the issue isn't whether the experiment proves there is spooky action at a distance...

If it doesn't then why conflate the two?

 

[name123]

If it doesn't then why conflate the two?

I did not think I had. I thought I was making a distinction between something being debatable, because there are differing opinions on the matter, and something being proven. Perhaps you can point out where you think I did.

 

[A.T.]

I thought I was making a distinction between something being debatable

But the statement you quoted is not debatable:

Quantum phenomena still obey relativistic causality.

 

[name123]

But the statement you quoted is not debatable:

Quantum phenomena still obey relativistic causality.

You quoted the wrong statement, the statement was:

One key physical constraint is that spacelike separated events cannot be causally related,

I pointed out some issues in post #130 which I thought indicated it was debatable.

 

[A.T.]

I pointed out some issues in post #130 which I thought indicated it was debatable.

How do those issues indicate that?

 

[weirdoguy]

I pointed out some issues in post #130 which I thought indicated it was debatable.

Do you know what 'spacelike separated' means?

 

[name123]

How do those issues indicate that?

Well I think those experimental results have been interpreted as being the measurement of one particle causally influencing the measurement of another particle even though the events were spacelike separated, and so have been interpreted as contradicting the statement "spacelike separated events cannot be causally related".

 

[name123]

Do you know what 'spacelike separated' means?

Roughly that the distance between the events was greater than light could travel in the time. Though I looked it up and I also saw the definition "Spacelike separation means that there exists a reference frame where the two events occur simultaneously, but in different places." Both seem to me compatible with what I was writing, so I am not sure why you asked.

 

[Herman Trivilino]

Well I think those experimental results have been interpreted as being the measurement of one particle causally influencing the measurement of another particle even though the events were spacelike separated, and so have been interpreted as contradicting the statement "spacelike separated events cannot be causally related".

No. Let one event be the detection of the spin of one member of an entangled two-particle system. Let the other event be the detection of the spin of the other member. Moreover, suppose those two events have a spacelike separation. If you are present at the first event it is true that as soon as you know the outcome of the first event you also know the outcome of the second, but you cannot send knowledge of that outcome and have it arrive at the location of the second event before that second event occurs.

 

[name123]

No. Let one event be the detection of the spin of one member of an entangled two-particle system. Let the other event be the detection of the spin of the other member. Moreover, suppose those two events have a spacelike separation. If you are present at the first event it is true that as soon as you know the outcome of the first event you also know the outcome of the second, but you cannot send knowledge of that outcome and have it arrive at the location of the second event before that second event occurs.

So what if you can't "send knowledge of that outcome and have it arrive at the location of the second event before that second event occurs"? The issue was whether the two events can be interpreted as being causally related.

 

[PeterDonis]

Are there not experiments where entangled particles are separated and they then subsequently have certain properties tested such as their spin for example, and that even if they are tested within a time frame which wouldn't allow for any causal effect from the testing of one even if traveling at the speed of light to have influenced the testing of the other, the spins for example are always opposite?

Does Bell's Inequality theorem not indicate that there could be no local hidden variables responsible?

Yes, there have been experiments verifying that quantum phenomena violate the Bell inequalities. No, that doesn't mean relativistic causality is violated. As I've already said.

 

[Ebeb]

The usual model is to treat spacetime as a 4d whole. You can select any 3d plane passing through your worldline "now" and call that "the universe now", but there's no significance to any particular choice. All are arbitrary 3d subsets of the 4d whole.

Looks fine to me.

We're not saying that the 3d subsets don't exist. Just that there are infinitely many ways to pick a subset and no good reason to prefer one choice over another.

Great.

No 3D world is physical. The physical world if 4D.

No 3D world is physical?
If the physical world is 4D, then 3D as a part of 4D has to be physical too.

Didn’t we have a really really long conversation about this already?

Yes, and I gave up because we couldn't get on the same wavelength.
Maybe we disagree on the meaning of physical.
As far as I understand Ibix, the events as such are indeed physical entities. If we consider an event 'car hits tree' then there is definitely car and a tree at a spacelike distance. There are physical object(s) at spacelike distance, hence the 3D world of simultameous events is physical.
And because there is no preference for a simultaneous collection, all 3D are physical. Which makes 4D physical too.

None. As @Dale and @Ibix have said, the usual model is to consider 4D spacetime as "real".

None? If the usual model is to consider 4D spacetime as "real", then the 3D collection of events is real too, see above, i.o.w. your -quote-" None" -unquote- cannot be correct.

I think Name123 too is a bit lost with above discrepancies. That's why he struggles with 'post topic Relative truth'.

 

[PeterDonis]

The issue was whether the two events can be interpreted as being causally related.

No, the issue is whether relativistic causality is violated. It isn't.

Asking whether two spacelike separated measurement events themselves are "causally related" is a different question. The strict answer to it if we take the viewpoint of relativistic causality is that the question has no meaning, because relativistic causality does not tell you which events can be "causally related". It just tells you that spacelike separated events have to commute--i.e., what happens at them does not depend on their ordering. The fact that the events commute does not prevent what happens at them from being correlated.

 

[PeterDonis]

If the usual model is to consider 4D spacetime as "real", then the 3D collection of events is real too

No, if the model considers all of 4D spacetime as real, then you cannot pick out any particular 3D collection of events as "real" while the others aren't. But you were implicitly saying that just one 3D collection of events was "real" and the others weren't.

If you're willing to say that "all 3D worlds are real", including 3D worlds that only contain events billions of years in our past here and now, and also 3D worlds that only contain events billions of years in our future here and now, then yes, you can say that. But then you can't draw the conclusions you are trying to draw from "3D worlds are real".

 

[Ebeb]

No, if the model considers all of 4D spacetime as real, then you cannot pick out any particular 3D collection of events as "real" while the others aren't. But you were implicitly saying that just one 3D collection of events was "real" and the others weren't.

I never said that. How can you pretend this after reading what I said about Ibix post? see #142

If you're willing to say that "all 3D worlds are real", including 3D worlds that only contain events billions of years in our past here and now, and also 3D worlds that only contain events billions of years in our future here and now, then yes, you can say that. But then you can't draw the conclusions you are trying to draw from "3D worlds are real".

No. You didn't understand me. I'm talking of 3D worlds or 3D universe 'now' as 3D sections made of simultaeous events.
What's you point of view on Ibix post #127 ?

 

[name123]

Yes, there have been experiments verifying that quantum phenomena violate the Bell inequalities. No, that doesn't mean relativistic causality is violated. As I've already said.

I never said it did mean relativistic causality is violated.

Dale had written:

One key physical constraint is that spacelike separated events cannot be causally related,

I had replied:

Well presumably this is up for debate given "spooky" action at a distance.

And then you wrote:

No, it isn't. Quantum phenomena still obey relativistic causality.

Though presumably you knew that quantum phenomena being interpreted as indicating that spacelike separated events can be causally related didn't imply that they were being interpreted as not obeying relativistic causality. So I found it slightly strange that you made such a switch on what I thought was supposed to be an educational site.

You seem to understand that many do interpret the experiments as indicating that spacelike separated events can be causally related and thus a claim that they cannot be is debatable. As I mentioned.

 

[name123]

No, the issue is whether relativistic causality is violated. It isn't.

No that was not the issue. That was what you tried to change the issue to as explained above in post #146

 

[PeterDonis]

I'm talking of 3D worlds or 3D universe 'now' as 3D sections made of simultaeous events.

Yes, but why pick out "now"? And why pick out your particular "now" (the events simultaneous to "here and now" in your rest frame), as opposed to someone else's "now" (the events simultaneous to "here and now" in someone else's frame)? Unless you want to give "now" some special status, there is no point to even mentioning it. And if all of 4D spacetime is real, then "now" has no special status.

What's you point of view on Ibix post #127 ?

See my post #128.

 

[PeterDonis]

I never said it did mean relativistic causality is violated.

Good. Then what have we spent the last hundred or so posts discussing?

You seem to understand that many do interpret the experiments as indicating that spacelike separated events can be causally related

I understand no such thing. I already explained what I understand in post #143.

 

[PeterDonis]

And if all of 4D spacetime is real, then "now" has no special status.

And similarly, if you take the alternative viewpoint I described in post #128 (that what is in your past light cone is what is "real"), then again "now" has no special status, so again there's no reason to even mention it.