# I Describing entanglement collapse with absolute time

#### kurt101

Summary
Why can't all time and distance in the universe be described in light seconds?
Why can't absolute time be used to describe events? Previously I tried to describe entanglement collapse on this forum in terms of absolute time, but I was told more or less this was not valid. I don't understand why.

If the proper time that we use is based on the fact that the speed of light in vacuum is constant no matter where we measure it then shouldn't we be able to describe any point in our universe relative to all other points in the universe in terms of light seconds where a light second is defined as the distance that light travels in free space in one second?

Can't we effectively use light seconds as both our absolute time and absolute position to describe the universe? In other words after N light seconds of time passing in the universe, I should be able to describe the distance between every point in the universe in light seconds.

Shouldn't I be able to make the statement that entanglement collapse happens in 0 light seconds and avoid the confusing language of saying that observers can't agree when an event really happened and avoid the confusing language of retro-causality?

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#### Mentz114

Gold Member
Summary: Why can't all time and distance in the universe be described in light seconds?

Why can't absolute time be used to describe events? Previously I tried to describe entanglement collapse on this forum in terms of absolute time, but I was told more or less this was not valid. I don't understand why.

If the proper time that we use is based on the fact that the speed of light in vacuum is constant no matter where we measure it then shouldn't we be able to describe any point in our universe relative to all other points in the universe in terms of light seconds where a light second is defined as the distance that light travels in free space in one second?

Can't we effectively use light seconds as both our absolute time and absolute position to describe the universe? In other words after N light seconds of time passing in the universe, I should be able to describe the distance between every point in the universe in light seconds.

Shouldn't I be able to make the statement that entanglement collapse happens in 0 light seconds and avoid the confusing language of saying that observers can't agree when an event really happened and avoid the confusing language of retro-causality?
Your question is puzzling. What do you mean by absolute time ? Which clock shows absolute time ?
A light-second is a unit of distance, there is nothing special about it.

#### kurt101

Your question is puzzling. What do you mean by absolute time ? Which clock shows absolute time ?
A light-second is a unit of distance, there is nothing special about it.
A light-second can be used as a unit of distance between points when combined with a 3 dimensional direction vector. A light-second can be used as a unit of time when considered as a 1 dimensional direction vector that only goes forward.

Another way to think of this is that I can simulate the universe on my computer by using light-seconds for my time and light-seconds for my distance and completely describe everything. In my simulation, I can say after N light-seconds of running the simulation what the distance in light-seconds between each object is.

#### Mentz114

Gold Member
A light-second can be used as a unit of distance between points when combined with a 3 dimensional direction vector. A light-second can be used as a unit of time when considered as a 1 dimensional direction vector that only goes forward.

Another way to think of this is that I can simulate the universe on my computer by using light-seconds for my time and light-seconds for my distance and completely describe everything. In my simulation, I can say after N light-seconds of running the simulation what the distance in light-seconds between each object is.
So what ? One could use any units and it would make no difference. Why not use light-milliseconds ?

#### Nugatory

Mentor
In my simulation, I can say after N light-seconds of running the simulation what the distance in light-seconds between each object is.
You can, but the simulation will only be accurate from the point of view of a simulated observer who is not moving. The problem here is that there is no universal observer-independent notion of the distance between objects that are in motion relative to one another.

#### Nugatory

Mentor
Shouldn't I be able to make the statement that entanglement collapse happens in 0 light seconds
A meter of time is the amount time it takes for light to travel a distance of one meter, so you could say that a light-second of time is the amount of time it takes for light to travel a distance of one light-second - but then you might just as well call it a second instead of a light-second.

But no matter what names you use for your units, there is a basic problem with saying that “collapse happens in 0” units of time. That’s tantamount to saying that the collapse happens at the same time at different locations in space, which conflicts with relativity of simultaneity.

#### kurt101

So what ? One could use any units and it would make no difference. Why not use light-milliseconds ?
I don't understand your counter-reply. The constant of speed of light seems like the best source for a universal tick. Whether we use for the units, light-seconds or light-milliseconds is irrelevant to my point and overall question which is why can't we describe events (like entanglement collapse) in terms of absolute time?

You can, but the simulation will only be accurate from the point of view of a simulated observer who is not moving.
You mean like God (the programmer)?

The problem here is that there is no universal observer-independent notion of the distance between objects that are in motion relative to one another.
If I pause the simulation, each object is going to have a specific distance in light-seconds between every other object. If I run it for a bit and then pause it, I can see exactly how each moving object changes relative to one another. So for all practical purposes it seems the "universal observer-independent notion" is extremely useful in understanding what is actually happening.

And again, if I can model everything in the universe accurately using absolute time, why shouldn't we use it in discussions?

#### Mentz114

Gold Member
I don't understand your counter-reply. The constant of speed of light seems like the best source for a universal tick. Whether we use for the units, light-seconds or light-milliseconds is irrelevant to my point and overall question which is why can't we describe events (like entanglement collapse) in terms of absolute time?

You mean like God (the programmer)?

If I pause the simulation, each object is going to have a specific distance in light-seconds between every other object. If I run it for a bit and then pause it, I can see exactly how each moving object changes relative to one another. So for all practical purposes it seems the "universal observer-independent notion" is extremely useful in understanding what is actually happening.

And again, if I can model everything in the universe accurately using absolute time, why shouldn't we use it in discussions?
There is no absolute time. Are you thinking of parameter time ? Are you familiar with special relativity ?

#### Nugatory

Mentor
If I pause the simulation, each object is going to have a specific distance in light-seconds between every other object.
Right, but pausing the simulation and looking at it is basically the same as recording where all the objects are at the same time, and the definition of “at the same time” is inherently frame-dependent.

#### kurt101

A meter of time is the amount time it takes for light to travel a distance of one meter, so you could say that a light-second of time is the amount of time it takes for light to travel a distance of one light-second - but then you might just as well call it a second instead of a light-second.
Obviously time can be translated between seconds and light-seconds, but one is a constant for all objects and the other can only be defined via an equation relative to that constant. For simplicity and understanding it makes more sense to choose the constant.

But no matter what names you use for your units, there is a basic problem with saying that “collapse happens in 0” units of time. That’s tantamount to saying that the collapse happens at the same time at different locations in space, which conflicts with relativity of simultaneity.
This point keeps being brought up and it is my understanding that the moderators on this forum don't agree on this. And those that do agree to this point can't effectively back it up other than to say in principle it conflicts, but never explains how in practice it conflicts. And maybe I am wrong on this perception that you can't back it up this in practice, but than I ask you to demonstrate this again in the most straight forward way possible, because I seem to miss it. Or point me to a previous solid explanation. Thanks!

#### kurt101

There is no absolute time. Are you thinking of parameter time ? Are you familiar with special relativity ?
I am familiar with special relativity and have read through basic proofs of it. For example I most recently have been reading through the proof from the book "Physics from Symmetry" by Jakob Schwichtenberg. The proof seems mostly straight forward and is based on how different observers in relative motion observe light reflected off a mirror. Even though this seems proof seems simple, I struggle at understanding all aspects of it, and I am open to the possibility that I am misunderstanding.

#### Mentz114

Gold Member
I am familiar with special relativity and have read through basic proofs of it. For example I most recently have been reading through the proof from the book "Physics from Symmetry" by Jakob Schwichtenberg. The proof seems mostly straight forward and is based on how different observers in relative motion observe light reflected off a mirror. Even though this seems proof seems simple, I struggle at understanding all aspects of it, and I am open to the possibility that I am misunderstanding.
I do not know that book. What proof are you referring to ?
There is no such thing as 'at the same time' for all observers.

#### Doc Al

Mentor
The constant of speed of light seems like the best source for a universal tick.
Realize that the speed of light is constant with respect to the observer of the light. Imagine a pulse of light. I measure the speed with respect to me to be "c". You measure the speed with respect to you to be "c". But according to my measurements, the speed of the pulse of light relative to you will be something other than "c".

#### DrChinese

Gold Member
I am familiar with special relativity...
General relativity tells us that time is influenced by the presence of mass. Time on Earth moves more slowly than time on a GPS satellite in space. So what could be an absolute clock?

Further: if collapse of entanglement were physical, it would still appear instantaneous regardless of reference frame. And if there were some preferred reference frame, this paper would be relevant:

#### PeterDonis

Mentor
Why can't absolute time be used to describe events?
Because there is no such thing.

This point keeps being brought up and it is my understanding that the moderators on this forum don't agree on this.
Your understanding is incorrect. There is no disagreement whatever on the fact that there is no "absolute time" in our best current theory of spacetime, which is General Relativity.

There is also no disagreement whatever on the fact that quantum entanglement cannot be used to send information between spacelike separated events (which is the correct technical way to say what is often sloppily said as "faster than light").

What there is disagreement on is the interpretation of quantum mechanics. But all interpretations of quantum mechanics make the same predictions for the results of all experiments, including experiments on entangled particles. So no QM interpretation disagrees on the two statements I made above.

#### kurt101

Realize that the speed of light is constant with respect to the observer of the light. Imagine a pulse of light. I measure the speed with respect to me to be "c". You measure the speed with respect to you to be "c". But according to my measurements, the speed of the pulse of light relative to you will be something other than "c".
Take the simple thought experiment of a photon reflecting off of a mirror with observers A and B. Observer B is stationary relative to the photon origin and mirror. Observer A starts at the photon origin and moves perpendicular to the origin and the mirror.

Observers A and B disagree about the time it took for the photon to reflect off of the mirror and come back to its origin, but they both assert that the photon traveled at the constant speed of light. Hopefully at this point I have not said anything incorrect or controversial; I am just repeating the thought experiment and derivation from the textbook in front of me "Physics from symmetry" which I assume is similar to many other derivations.

Now do you or anyone else disagree that at any point during this experiment that I as an independent all knowing observer can assign a distance in light-seconds between any two observers in this experiment? You should not disagree since it is assumed in the derivation that the speed of light is constant between any two points in order for the derivation to work.

If I as an all knowing observer can assign a distance in light-seconds between any two observers and all observers share the same value C then I should be able to pause the universe and make a single unique configuration where this has to be true. I should be able to unpause the universe, run it for a while, and after n * C ticks later do this again. If I can accurately model the universe as an all knowing independent observer, shouldn't we acknowledge that thinking in terms of absolute time is a completely legitimate and more importantly a useful way to think of the universe?

To the best of ability to understand; it seems like those who say absolute time does not exist is because they don't want to think in terms of an independent all knowing observer even though the universe can accurately be modeled this way and reproduce all of the same predictions. Is this correct? Or what mistake am I making in coming to this conclusion?

#### Doc Al

Mentor
Take the simple thought experiment of a photon reflecting off of a mirror with observers A and B. Observer B is stationary relative to the photon origin and mirror. Observer A starts at the photon origin and moves perpendicular to the origin and the mirror.
This description is a bit confusing. I assume you are describing the standard "light clock" derivation, that is repeated in Section 2.1 of "Physics from Symmetry"?
Observers A and B disagree about the time it took for the photon to reflect off of the mirror and come back to its origin, but they both assert that the photon traveled at the constant speed of light. Hopefully at this point I have not said anything incorrect or controversial; I am just repeating the thought experiment and derivation from the textbook in front of me "Physics from symmetry" which I assume is similar to many other derivations.
In that book, A, B, and C represent events, not observers. Nonetheless, you can certainly have a light clock in one frame (where the mirrors are at rest) that is also observed from another frame. Yes, the two observers will disagree on the time it takes for the photon to reflect off the mirror and return.
Now do you or anyone else disagree that at any point during this experiment that I as an independent all knowing observer can assign a distance in light-seconds between any two observers in this experiment? You should not disagree since it is assumed in the derivation that the speed of light is constant between any two points in order for the derivation to work.
I don't know what you mean by the distance between two observers in this context. (Why not refer to the book, since I have it as well?) What two observers? Anyway, there's nothing special about you and your frame of reference. Any observer can "measure" the distance between two "observers" at a given time and express that distance in light-seconds. Different observers will measure different distances, in most cases. So what?

#### kurt101

In that book, A, B, and C represent events, not observers.
Sorry, yes of course you are correct. I am not sure why I used A and B to refer to the observers. I was just going from what was in my head and not directly from the book when I named the observers.

I don't know what you mean by the distance between two observers in this context. (Why not refer to the book, since I have it as well?) What two observers?
Yes, please use first and second observer, like the book does going forward. First observer is at rest with respect to the origin and second observer is moving with a constant velocity u to the left of the origin.

Anyway, there's nothing special about you and your frame of reference. Any observer can "measure" the distance between two "observers" at a given time and express that distance in light-seconds. Different observers will measure different distances, in most cases. So what?
I am thinking hard on this. Thanks.

#### Doc Al

Mentor
I am thinking hard on this.
Good! Keep at it. (I get the feeling that you think that measuring distances using "light-seconds" somehow makes it universally agreed upon. Not so!)

Get your understanding of special relativity under control before worrying about describing entanglement.

#### PeterDonis

Mentor
do you or anyone else disagree that at any point during this experiment that I as an independent all knowing observer can assign a distance in light-seconds between any two observers in this experiment?
Yes, I disagree. There is no such thing as "absolute distance" any more than there is "absolute time". Nor is there any such thing as an "independent all knowing observer" whose distance and time observations have some sort of privileged or absolute status.

You should not disagree since it is assumed in the derivation that the speed of light is constant between any two points in order for the derivation to work.
Yes, it is assumed that the speed of light is constant. That does not mean there is an absolute distance or an absolute time.

it seems like those who say absolute time does not exist is because they don't want to think in terms of an independent all knowing observer even though the universe can accurately be modeled this way and reproduce all of the same predictions. Is this correct?
No.

what mistake am I making in coming to this conclusion?
The mistake of assuming that there is an absolute distance and time and that there is such a thing as an "independent all knowing observer".

#### PeterDonis

Mentor
Get your understanding of special relativity under control before worrying about describing entanglement.
This is good advice. And with it, this thread is closed since all we are doing at this point is repeating the same things.

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