Does Special Relativity Change Our Perception of Others?

[EclogiteFacies]

TL;DR Summary

Is the Andromeda Paradox not basically time travel?!

Hi all,

I'm a bit nervous about the implications of relativity, not the block universe stuff I can work with that..

What worries me regards planes of simultaneity, when I'm walking away from you my plane of simultaneity will contain you from your past, so the you in my reference frame wouldn't line up with the real you. (honestly I think I've got this wrong and I need to some more research)

Anyway!

The Andromeda Paradox seems to say that if a fella in Andromeda moves away from us or towards us the notion of now on their plane of simultaneity goes all over the place, but here where we are there's a notion of time, it's not like we fly backwards and forwards in time when someone in Andromeda moves around. Surely if this person in Andromedas idea of now is flying all over the place they're basically travelling backwards and forwards in time constantly...

I gather my confusion comes from mixing up things like proper time and coordinate time and to be honest not really understanding relativity

Thanks all any advice would be lovely.

 

[PeroK]

I gather my confusion comes from mixing up things like proper time and coordinate time and to be honest not really understanding relativity

Thanks all any advice would be lovely.

The simultaneity convention used by something in the Andromeda galaxy is of no physical significance. No more so than if someone in London decides at 8am to assume that it's 8am around the globe. That's fine, as long as they stick to that convention. It doesn't mean, however, that you suddenly get daylight in San Francisco.

 

[Dale]

The Andromeda Paradox seems to say that if a fella in Andromeda moves away from us or towards us the notion of now on their plane of simultaneity goes all over the place, but here where we are there's a notion of time, it's not like we fly backwards and forwards in time when someone in Andromeda moves around. Surely if this person in Andromedas idea of now is flying all over the place they're basically travelling backwards and forwards in time constantly...

Simultaneity is simply a matter of convention. There is no physical content to simultaneity meaning that there is no possible physical experiment that can depend on the simultaneity convention. The universe "cares" about causality, not simultaneity. The universe requires that causes must precede effects, but for events that are not causally connected the choice of ordering is entirely a human conceit.

 

[EclogiteFacies]

Simultaneity is simply a matter of convention. There is no physical content to simultaneity meaning that there is no possible physical experiment that can depend on the simultaneity convention. The universe "cares" about causality, not simultaneity. The universe requires that causes must precede effects, but for events that are not causally connected the choice of ordering is entirely a human conceit.

Do you think my anxiety regarding other observers is silly? As in I am failing to grasp relativity

 

[Dale]

Do you think my anxiety regarding other observers is silly? As in I am failing to grasp relativity

Yes, your anxiety is silly.

I am glad that you are interested in learning relativity, but in both this thread and your previous one you have expressed some sort of emotional distress at the topic. That is not reasonable, particularly since your distress has, in both cases, been entirely based on the non-physical concepts/conventions. There should be no more angst for these topics than for the fact that we use right-handed coordinates instead of left-handed coordinates.

Relativity is fun to learn. It is fun to find out how the universe works. There is no reason for anxiety on the subject beyond the normal healthy anxiety inherent in the challenge of learning a difficult topic.

 

[EclogiteFacies]

Yes, your anxiety is silly.

I am glad that you are interested in learning relativity, but in both this thread and your previous one you have expressed some sort of emotional distress at the topic. That is not reasonable, particularly since your distress has, in both cases, been entirely based on the non-physical concepts/conventions. There should be no more angst for these topics than for the fact that we use right-handed coordinates instead of left-handed coordinates.

Relativity is fun to learn. It is fun to find out how the universe works. There is no reason for anxiety on the subject.

Thank you for your help. Ye there's definitely an emotional thing here in the sense my misunderstanding is making the world seem much more weird than it is ahaha.
so what is it I am conflating here? Seems I'm over interpreting things and taking maths and coordinates to be entirely physically real

 

[PeroK]

Do you think my anxiety regarding other observers is silly?

Yes.

As in I am failing to grasp relativity

The restricted sense in which simultaneity is physically meaningful is hard to grasp. If you have a 100m race, then it's essential that the runners all hear the starting gun "at the same time". This has meaning in the rest frame of the sports stadium because we have essentially a local event. Also, the maximum possible loss of simultaneity is very small. It's about the width of the track divided by the speed of light. All your observers in Andromeda would agree that the race was fair - in the sense that the runners all heard the gun at the same time (to within a few nanoseconds).

What the observers in Andromeda cannot do is uniquely specify (with any physical significance), when in local Andromeda time the race on Earth took place. There is a potential range of two million years either way. It's of no physical significance how they choose to relate the current events on Earth to their own local time.

This is where mathematics is underestimated. The mathematical calculations are the only way to really understand what relativity is saying here. Without mathematics, it can become a philosophical quagmire - even for the smartest minds.

 

[PeterDonis]

@EclogiteFacies before getting upset about the so-called Andromeda "paradox", please read this Insights article:

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

 

[EclogiteFacies]

@EclogiteFacies before getting upset about the so-called Andromeda "paradox", please read this Insights article:

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

I'll take a read thank you! I was just curious about the outcomes assuming block time is correct.

 

[PeterDonis]

I was just curious about the outcomes assuming block time is correct.

Even if the block universe is correct, my comments in the Insights article about simultaneity are still valid. Briefly, a surface of simultaneity has no physical meaning, and it makes no sense to think of everything before a surface of simultaneity as "the past" in the sense we normally think of that term. The actual physically meaningful division of spacetime in relativity is into three regions, not two: the past light cone (which works like we normally think of the past), the future light cone (which works like we normally think of the future), and the spacelike separated region, which I refer to as "elsewhere" (using Roger Penrose's terminology), and which doesn't work like our normal intuitions for either the future or the past. Since in the Andromeda scenario, Andromeda and Earth are spacelike separated for the events under discussion, they are in the "elsewhere" region and you can't use any of your ordinary intuitions about the past or the future.

 

[EclogiteFacies]

So to avoid having to make another thread and getting this off my chest.

My anxiety regarding special relativity and my notion of other observers is misfounded.

My anxiety stems from the following;

You are sat in the living room, I walk away from you into the kitchen. According to time dilation we see each others time slow down. My plane of simultaneity crosscuts a period in your past (granted at this rate its going to be a fraction of a second in your past). I'm anxious because this seems to imply that if we take things in my reference frame to be real then the notion of you I have in my reference frame is not the same notion of you in your reference frame. Kinda resulting in two versions of you. This is a mistake and I will figure this out
However this conversation has been enlightening it seems I am over interpreting the physical meanings of things we see on space time diagrams. Attaching physical meaning where it's not necessary.

I think I am in a way viewing reference frames as almost entirely separate universes which I gather is wrong. We are seeing the same universe.

I ought to go study the maths.

Thank you all any further advice that may quell my nervousness would be hugely appreciated. I am thankful for this community.

 

[EclogiteFacies]

Even if the block universe is correct, my comments in the Insights article about simultaneity are still valid. Briefly, a surface of simultaneity has no physical meaning, and it makes no sense to think of everything before a surface of simultaneity as "the past" in the sense we normally think of that term. The actual physically meaningful division of spacetime in relativity is into three regions, not two: the past light cone (which works like we normally think of the past), the future light cone (which works like we normally think of the future), and the spacelike separated region, which I refer to as "elsewhere" (using Roger Penrose's terminology), and which doesn't work like our normal intuitions for either the future or the past. Since in the Andromeda scenario, Andromeda and Earth are spacelike separated for the events under discussion, they are in the "elsewhere" region and you can't use any of your ordinary intuitions about the past or the future.

This really helped further see where I'm making mistakes. Regarding my previous post.

 

[PeterDonis]

We are seeing the same universe.

Yes. Different frames are just different "viewpoints" on the same universe. But different frames will agree on any actual physical event.

 

[EclogiteFacies]

Yes. Different frames are just different "viewpoints" on the same universe. But different frames will agree on any actual physical event.

Thanks for everything. Nice to hear I've misinterpreted!

 

[Dale]

what is it I am conflating here? Seems I'm over interpreting things and taking maths and coordinates to be entirely physically real

That is what you are conflating. Coordinates are just labels, they are no more real than your postal code.

Hopefully you are used to the concept that the origin of your coordinates is not real. There is nothing physical that demands that we place the origin in a certain place. It turns out that your velocity and your simultaneity convention are similarly unphysical.

my misunderstanding is making the world seem much more weird than it is ahaha.

The world is indeed pretty weird, but the main thing to realize is that no matter how weird you find it to be it was just as weird yesterday. There is no more reason to worry than there was previously, the only thing that is changing is your understanding. The world is no more nor less weird than it ever was.

My plane of simultaneity crosscuts a period in your past (granted at this rate its going to be a fraction of a second in your past).

While that is true, it has no physical consequences. Nothing on your plane of simultaneity can affect you now.

 

[EclogiteFacies]

That is what you are conflating. Coordinates are just labels, they are no more real than your postal code.

Hopefully you are used to the concept that the origin of your coordinates is not real. There is nothing physical that demands that we place the origin in a certain place. It turns out that your velocity and your simultaneity convention are similarly unphysical.The world is indeed pretty weird, but the main thing to realize is that no matter how weird you find it to be it was just as weird yesterday. There is no more reason to worry than there was previously, the only thing that is changing is your understanding. The world is no more nor less weird than it ever was.While that is true, it has no physical consequences. Nothing on your plane of simultaneity can affect you now.

So is there no physical meaning to my plane of simultaneity being in your past. Does it lead to any weird consequences that alter they way we think about other observers?

 

[Ibix]

Does it lead to any weird consequences that alter they way we think about other observers?

No. Carelessly switching frames can lead to a few eyebrow-raising things (like the Andromeda paradox), but it's just a result of sloppy book-keeping. It's very like getting on a flight at 7pm and arriving at 6.30pm and wondering if the plane is a time machine - no, just an amusing side effect of changing your clock settings. But potentially a confusing effect if you don't understand why it happens.

Relativity just introduces new types of clock settings to mess with.

 

[PeroK]

Does it lead to any weird consequences that alter they way we think about other observers?

It's important that it can't and doesn't. Otherwise, the universe would make no sense.

 

[PeterDonis]

is there no physical meaning to my plane of simultaneity being in your past.

That's correct. As I said in an earlier post, the only physically meaningful boundaries are the past and future light cones.

Does it lead to any weird consequences that alter they way we think about other observers?

The presence of the spacelike separated "elsewhere" region alters the way we should think about the concept of "now". Either that concept needs to be discarded, or it needs to be updated to not represent a single plane of simultaneity but the entire spacelike separated "elsewhere" region. That means there is a huge uncertainty about what is happening "now" at locations far away; for example, if we ask what is happening "now" in the Andromeda galaxy, that encompasses a range of several million light years along the worldline of any star or planet in that galaxy, so the question itself is much less meaningful. (By contrast, if you ask what is happening "now" in the next room, the range is only nanoseconds, which is many orders of magnitude less than the time it takes you to consciously perceive anything, so on that scale the concept of "now" works the way you would normally expect.)

 

[EclogiteFacies]

Thank you all I really appreciate all of you.
I feel a lot better now.

Just wanna say sorry for putting my anxieties on this forums. Just didn't know who else to ask!

Thank you!

 

[PeterDonis]

Thank you all I really appreciate all of you.

You're welcome! Thanks for the appreciation.

 

[EclogiteFacies]

That's correct. As I said in an earlier post, the only physically meaningful boundaries are the past and future light cones.The presence of the spacelike separated "elsewhere" region alters the way we should think about the concept of "now". Either that concept needs to be discarded, or it needs to be updated to not represent a single plane of simultaneity but the entire spacelike separated "elsewhere" region. That means there is a huge uncertainty about what is happening "now" at locations far away; for example, if we ask what is happening "now" in the Andromeda galaxy, that encompasses a range of several million light years along the worldline of any star or planet in that galaxy, so the question itself is much less meaningful. (By contrast, if you ask what is happening "now" in the next room, the range is only nanoseconds, which is many orders of magnitude less than the time it takes you to consciously perceive anything, so on that scale the concept of "now" works the way you would normally expect.)

Just to double check we are not denying the existence of things outside our light cones just the status of those things is completely unknowable as we can never access it.

 

[PeroK]

Just to double check we are not denying the existence of things outside our light cones just the status of those things is completely unknowable as we can never access it.

No, it's just that are neither definitely in the past nor definitely in the future. Remember that past and future light cones change over time. Assume that we have a machine on Mars that sends us images. If we receive an image now (our local time), then the event of sending the image is in our past light cone. But, it wasn't in our past light cone ten minutes ago. And, it also wasn't in our future light cone ten minutes ago. In short, the event was causally disconnected from the event "Earth, ten minutes ago". It didn't remain causally disconnected from Earth. Once the light from the event reached Earth, it was unambiguously in our past (and all reference frames would agree on that; as they agree on the past and future light cones of any event).

 

[PeroK]

PS to learn the physics, you have to break your mind of the fallacy of dividing events into past and future and divide them according to the causal structure of spacetime. That can be hard work. It's a discipline.

 

[EclogiteFacies]

So to end this thread.

Special relativity, time dilation and the block universe do not mean that the observers I communicate with represent versions of themselves incompatible with that that observers reference frame.

If you are say on the moon your perception / perspective from your frame exists for me, I just have no access to it.

Furthermore, we can calculate a spatially separated observers 'proper time' to derive a notion of their time.

Special relativity has no real implications on our communication and notions of one another. If I am moving away from you my plane of simultaneity may cut a point in your past in your reference frame. But the outcome of this is not that there are two versions of you, or that the universe in my reference frame contains a notion of you incompatible with your own notion of yourself from your reference frame.. It's not necessarily physically meaningful.

A sufficient grasp of special relativity will in turn show that this worldview and physical theory makes sense.

Makes sense in such a way that it does not change our relationships, understanding of of other people / observers and does not give us any reason to feel anxious. Thank you all, if I'm right here and anyone has any final bits of advice I'm very happy with everything. Thanks again all!

 

[Dale]

Just to double check we are not denying the existence of things outside our light cones just the status of those things is completely unknowable as we can never access it.

This distinction is not physically meaningful. In other words, there is no possible experiment that you could design, even in principle, which could ever distinguish between "things outside our light cone do not exist" and "things outside our light cone are completely unknowable". So you can make either assertion as a matter of personal preference, for any reason or no reason. Neither position can be shown wrong.

The point is that this is a distinction that exists only in human minds. Nature does not make this distinction. So the distinction itself does not matter physically.

If you are say on the moon your perception / perspective from your frame exists for me, I just have no access to it.

I don’t think that this is a physically meaningful distinction. Meaning I don’t think there is an experiment that could distinguish these two statements even in principle.

It's not necessarily physically meaningful.

Yes. There are many physically meaningful things in relativity that are very strange. But the specific two that have aroused your anxiety are not physically meaningful.

 

[PeterDonis]

Just to double check we are not denying the existence of things outside our light cones

Correct.

just the status of those things is completely unknowable as we can never access it.

No, that's too strong. We can extrapolate forward from the data in our past light cone to make at least a prediction about what the status of those things is in the spacelike separated region (for example, we can use the latest data we have on the Andromeda galaxy and evolve it forward in time using the laws of physics), and as we move into our own future, we accumulate more data (so a year from now we will have a year's worth of new data on the Andromeda galaxy that we can use to update our model).

 

[jbriggs444]

In the networking trade, we face situations similar to the Andromeda paradox every day.

If I do a ping test to measure round trip time between Washington, DC and Colorado Springs, CO and see a result of 40 milliseconds, I have no way of telling whether that is 10 milliseconds on the forward trip and 30 milliseconds on the return. Or 30 milliseconds on the forward and 10 milliseconds on the return. Or the normally expected 20/20 split.

The good news is that none of our networking protocols (except, perhaps, NTP) care. Only round trip time has meaningful network significance.

Rather than causing anxiety, special relativity actually provides comfort. It assures us (in some back-handed sort of sense) not only that asymmetric latency does not cause problems, it cannot cause problems.

[Asymmetric packet loss and asymmetric congestion is a whole other story and matters greatly]

 

[EclogiteFacies]

Yes. There are many physically meaningful things in relativity that are very strange. But the specific two that have aroused your anxiety are not physically meaningful.

Does the distinction between coordinate time and proper time come into this?

As I gather coordinate time is just a label and isn't meaningful. Proper time is the time experienced by the spatially separated observer and that's the time that's important in understanding how other observers see the world.

What is it I am applying too much physical meaning to?

 

[EclogiteFacies]

Does anyone here think my anxiety is reasonably founded or are my anxieties pretty much only founded on misunderstanding?

 

[vanhees71]

So to avoid having to make another thread and getting this off my chest.

My anxiety regarding special relativity and my notion of other observers is misfounded.

No matter, which subject in physics you consider there's no reason to develop an anxiety, because what physics as a natural science does is simply to observe Nature and try to order the findings of these observations in mathematical theories and models, i.e., it doesn't and can not change anything what's not "there" in Nature.

In the context of relativity, it's clear that relativity simply is a better way to order events in space and time than the Newtonian space-time description is. Of course, as far as we know at the present stage of scientific knowledge, Nature always was behaving more as described by relativity than by Newtonian physics. Newtonian physics is simply a theory, though being very successful within its realm of applicability, which has a limit range of applicability. It could also well be that one day one finds by an observation that also (general) relativity is only approximately valid within some limited range of applicability.

So there is no reason to be anxious about anything we find out by using the scientific method. It's always to be expected that you find more accurate descriptions about the phenomena in Nature, which of course occur independent of our descriptions.

 

[martinbn]

Does anyone here think my anxiety is reasonably founded or are my anxieties pretty much only founded on misunderstanding?

What are you anxious about?

 

[EclogiteFacies]

What are you anxious about?

I summarised it in one of the above posts number 25.

Thanks!,

 

[martinbn]

I summarised it in one of the above posts number 25.

Thanks!,

There it says

...does not give us any reason to feel anxious.

So, are you still anxious? Why? About what?

 

[EclogiteFacies]

There it says

So, are you still anxious? Why? About what?

Well I was just double checking to see if my summary was mistaken and special relativity does not actually our notions of other people

That's what's making me shook. I just to know if my reasoning behind what was causing me anxiety was faulty