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Old 22nd November 2022, 04:39 PM   #121
Robin
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My science fiction story is that an experiment is performed in which subjects are shown a video, sent back in time, of everything they do in the next hour.

They are offered a million dollars if they can do even one thing differently from the thing they see themselves doing in the video.

To make it interesting the mad philosopher who is running the experiment has poisoned the coffee of some of the subjects.so that when they see themselves dying they have an extra incentive.

The control is another group of subjects who are never shown the video.

There seem to be two possible endings. First everyone picked up their million dollars and no one drinks the poisoned coffee. Since the video must have come from somewhere the conclusion would be that it happened in a different universe.

The other ending I'd that all the subjects find themselves compelled to do everything they see on the video, including drinking the coffee that they know will kill them, and no one collects.

In his trial the mad philosopher points out that the only possible conclusion to the results of the experiment is that the deaths were inevitable and could not possibly have been prevented.

But of course the first ending requires that the second ending also happened.

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Old 22nd November 2022, 04:55 PM   #122
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But what you can't do is come up with a scenario in which causality is actually violated.

You can write it up to the brink of the causality being violated but you can't go the next step and actually describe causality being violated. Because everything you could write would be something that could happen, were the laws of physics different.

Try it, the train is speeding towards a break in the tracks, in full knowledge that there is a break in the track ahead. So go on what happens next? Describe the part where the causality is actually violated.

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Old 22nd November 2022, 10:01 PM   #123
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Oh that’s easy! It goes ‘bip!’ and a little text box pops up that says ‘illegal function in line 885.’

Hey if your mad philosopher isn’t legally culpable then nobody is, he’s still the guy that has the idea to put the poison in the coffee. If he wasn’t sure whether or not the subjects would have any other choice but to drink it then he’s at least creating a lethal hazard at that point. If he’s locked in to the choice then you just disproved functional free will and if you let him off on such flimsy grounds then obviously you must abolish the entire concept of culpability for crime (indeed for anything at all)!

Of course if that were actually the case then it being very inconvenient would not make it less true.

Time travel! Nothing but trouble!
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Old 22nd November 2022, 10:55 PM   #124
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<sorry for late response- been busy>

Originally Posted by pzkpfw View Post
Again with "distortion".

That implies there's something "undistorted". No.
Of course it is a distortion. Or put better; it can be perceived as a distortion.

A single observeer only experiences time 'normally'. A second is a second. An observer (for our purposes, a conscious entity) can only observe time behaving differently from his experience, and differently than he knows the subject is experiencing it, when the other is moving away at a brisk clip.

The time appears distorted, as compared to the one and only way that he experiences time, and that he knows the other does. 'Undistorted' would simply mean the only way a human experiences time.

If I call you on my phone which has a damaged microphone (it does), my ordinarily songbird-like voice would sound like a walrus being raped in a closet. You would perceive my voice as distorted, even though it is entirely real for you, but you know that is not what it sounds like on the other end. It is a relative term used in the language, is all.

Quote:
Reality for Alice is reality. Reality for Bob is reality. Neither is a distortion. They are just different.
If you really believed that, what would the words 'time dilation' mean? It only has meaning compared to an observer who experiences time in only one way. Hence it is distorted from the way ******* everyone experiences time.


Quote:
Also noting: the point about distance increasing between them (or decreasing) ... that just means they are not at rest with respect to each other. They are not comoving.

That in turn means their time is not the same, it can't be (for light speed to be the same for them).

It's not about the distance itself. It's not about whether that's a large distance or a small distance. It's just about that distance changing (so they are not at rest with respect to each other).


I might be on an observatory on the Moon.

Seven (!) rockets could zoom past me in seven different directions and speeds. The dangerous pilots could pass me at almost the same time (according to me) with just a gnats wings space between them all; none of that stops them having seven different clock rates (according to me, and to each other).


(Now over vast distances, it's true that "now" becomes kind of meaningless. Alice and Bob might both be drifting in deep space, in voids between different galaxies. They could technically be at rest with respect to each other, their clocks could be ticking at the same rate. But when even light would take many thousands/millions/... of years to get from one to another, what does that even mean? However, that's not really the topic of this thread. ETA: further reading - "light cone".)


--------------------------
ETA2: different scenario to illustrate the "distance" thing ...

http://www.internationalskeptics.com...ictureid=13252

Alice and Carol are comoving (at rest with each other) so their clocks will agree. Technically, because of the different angle the Alice-Bob speed won't quite be the same as the Carol-Bob speed, so for Bob the Alice and Carol clocks will be different. (But for the purpose of a thread like this they'd be treated as the same.)

Main point: the Alice-Bob distance being long and the Carol-Bob distance being short, isn't the point.
Yes, I get that. what I am trying to do is focus on how this relates to the OP question. As I see it, theprestige posits that he sees an effect, then goes to a point where that effect has not happened yet. As I am seeing it, he could only observe that far off place, not interact with it. We can't for instance, sit in our living rooms with someone who's time is running at half our speed, yes? Twould be a nuisance asking him to pass the salt.

So what I am driving at, is to ask whether places flying away from each other so fast and far as to produce that kind of time dilation could ever in fact interact in any way, magic phones and instantaneous teleporters excluded?
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Old 23rd November 2022, 12:06 AM   #125
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Originally Posted by Thermal View Post
...

Yes, I get that. what I am trying to do is focus on how this relates to the OP question. As I see it, theprestige posits that he sees an effect, then goes to a point where that effect has not happened yet. As I am seeing it, he could only observe that far off place, not interact with it. We can't for instance, sit in our living rooms with someone who's time is running at half our speed, yes? Twould be a nuisance asking him to pass the salt.

So what I am driving at, is to ask whether places flying away from each other so fast and far as to produce that kind of time dilation could ever in fact interact in any way, magic phones and instantaneous teleporters excluded?
It's not about the observation or going to a point.

It's simply that dilation exists and happens.

But as long as all communication or movement is at c or less, then no causality breaking effects will occur.

Alice and Bob can radio each other (radio waves travelling at c), and all is well.

It's only when FTL or instant communication or movement is postulated that the issues pop up.
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Old 23rd November 2022, 12:09 AM   #126
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Originally Posted by pzkpfw View Post
It's not about the observation or going to a point.

It's simply that dilation exists and happens.

But as long as all communication or movement is at c or less, then no causality breaking effects will occur.

Alice and Bob can radio each other (radio waves travelling at c), and all is well.

It's only when FTL or instant communication or movement is postulated that the issues pop up.
The OP specifically posed that.
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Old 23rd November 2022, 12:10 AM   #127
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Originally Posted by Thermal View Post
The OP specifically posed that.
Yes, and frankly it's kind of garbled. The pages of explanation that followed are about what FTL vs causality is really about.
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Old 23rd November 2022, 12:58 AM   #128
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Arrow

Originally Posted by Thermal View Post
We can't for instance, sit in our living rooms with someone who's time is running at half our speed, yes?
We could sit in our living room with someone whose time was running at half our speed.

Only very, very briefly but we could have someone whose time was running at half our speed within a couple of feet.
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Old 23rd November 2022, 02:44 AM   #129
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Originally Posted by Robin View Post
There seem to be two possible endings. First everyone picked up their million dollars and no one drinks the poisoned coffee. Since the video must have come from somewhere the conclusion would be that it happened in a different universe.

The other ending I'd that all the subjects find themselves compelled to do everything they see on the video, including drinking the coffee that they know will kill them, and no one collects.
Forget the time travel aspect; put a cup of coffee in front of me, offer me a million dollars not to drink it, and tell me it's poisoned as well, and I almost certainly won't drink the coffee. Unless it's a really long time since I last had a coffee, in which case, to hell with it, I need coffee.

Dave
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Old 23rd November 2022, 04:31 AM   #130
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Originally Posted by Olmstead View Post
If you really want to split hairs, it's not that FTL communication causes time paradoxes, it's that it's impossible to come up with a way to make FTL communication work in our universe without causing time paradoxes. Even if you could somehow "correct" the communication between two people with different velocities, that same correction would break down when you got a person with a third velocity involved.
The simple solution is to slaughter all life in the universe other than two people.
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Old 23rd November 2022, 04:32 AM   #131
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Originally Posted by sphenisc View Post
The simple solution is to slaughter all life in the universe other than two people.
Nah, you need to reduce the universe to one photon.
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Old 23rd November 2022, 04:34 AM   #132
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Originally Posted by Robin View Post
My science fiction story is that an experiment is performed in which subjects are shown a video, sent back in time, of everything they do in the next hour.

They are offered a million dollars if they can do even one thing differently from the thing they see themselves doing in the video.

To make it interesting the mad philosopher who is running the experiment has poisoned the coffee of some of the subjects.so that when they see themselves dying they have an extra incentive.

The control is another group of subjects who are never shown the video.

There seem to be two possible endings. First everyone picked up their million dollars and no one drinks the poisoned coffee. Since the video must have come from somewhere the conclusion would be that it happened in a different universe.

The other ending I'd that all the subjects find themselves compelled to do everything they see on the video, including drinking the coffee that they know will kill them, and no one collects.

In his trial the mad philosopher points out that the only possible conclusion to the results of the experiment is that the deaths were inevitable and could not possibly have been prevented.

But of course the first ending requires that the second ending also happened.
There are - probably unsurprisingly - many short stories and even novels that have explored this idea.
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Old 23rd November 2022, 02:48 PM   #133
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Originally Posted by Darat View Post
There are - probably unsurprisingly - many short stories and even novels that have explored this idea.
Are there? I'd appreciate it if you could mention at least one. I would be Interested in the result they chose -

In my experience science fiction.tends to skim over the method of paradox resolution. There are stories where people change the future - but they don't tend to go into how they were able to do this - what happened to the other future.

I don't know of any story where paradoxes are explicitly tested.
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Old 23rd November 2022, 03:04 PM   #134
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Best time travel paradox handling ever: https://en.wikipedia.org/wiki/Roswell_That_Ends_Well

Futurama S3E19. Recommend watching somewhere, not reading the wiki page.
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Old 23rd November 2022, 06:15 PM   #135
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Originally Posted by Dave Rogers View Post
Forget the time travel aspect; put a cup of coffee in front of me, offer me a million dollars not to drink it, and tell me it's poisoned as well, and I almost certainly won't drink the coffee. Unless it's a really long time since I last had a coffee, in which case, to hell with it, I need coffee.

Dave


I don't know about poison, but I sometimes think if I was told that someone spat in my coffee I'd say "I need coffee" and drink it.
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Old 23rd November 2022, 06:36 PM   #136
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Originally Posted by pzkpfw View Post
Best time travel paradox handling ever: https://en.wikipedia.org/wiki/Roswell_That_Ends_Well

Futurama S3E19. Recommend watching somewhere, not reading the wiki page.
I loved that episode, but my favourite handling of time travel id is still Bill & Teds solution to getting into the locked cell "After this is over, remember to go back in time, steal your Dad's keys and put them under this rock" "Hey, it was me who took my Dad's keys."
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Old 24th November 2022, 04:50 AM   #137
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Maybe the universe is kind of chill about the whole thing, and particles will be cloned/destroyed as needed to keep the show going. It breaks a few dozen natural laws, but then so does FTL travel in the first place.
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Old 25th November 2022, 08:58 AM   #138
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Originally Posted by Robin View Post
We could sit in our living room with someone whose time was running at half our speed.

Only very, very briefly but we could have someone whose time was running at half our speed within a couple of feet.
Pretty sure we couldn't sit with them. Pretty sure that would have to be flying through the room at near lightspeed.

As far as if we "can" do so, we prob have a long way to go in creating something that could propel a human on Earth at that kind of velocity, not even getting into the piloting mechanisms needed to steer through your living room unscathed.

Pretty sure "we can't" is the right descriptor, here.
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Old 25th November 2022, 09:54 AM   #139
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Originally Posted by Thermal View Post
Pretty sure we couldn't sit with them. Pretty sure that would have to be flying through the room at near lightspeed.
What do you think Robin meant by "Only very, very briefly"?

Originally Posted by Thermal View Post
As far as if we "can" do so, we prob have a long way to go in creating something that could propel a human on Earth at that kind of velocity, not even getting into the piloting mechanisms needed to steer through your living room unscathed.

Pretty sure "we can't" is the right descriptor, here.
None of which is the point.

The question in the OP was "Is violating causality via FTL really a problem? Can someone explain?" As that's about observers in relative motion we have scenarios where the observers are moving (in respect to each other) in some way.

Sure, you couldn't really "pass the salt" (or go that fast through an atmosphere without turning the living room into ash) but the OP question wasn't about salt passing.


You've previously accepted made-up numbers in the examples, and not worried (for example) exactly how Alice and Bob boil eggs in weightlessness (I'll now suggest centrifuges, so they can use regular kitchen equipment); why complain about this hypothetical?

Last edited by pzkpfw; 25th November 2022 at 10:01 AM. Reason: No coffee yet
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Old 25th November 2022, 11:12 AM   #140
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Originally Posted by pzkpfw View Post
What do you think Robin meant by "Only very, very briefly"?
I think Robin meant to say "while I get your point and agree, I think I'll say that you are wrong by claiming a scenario with no context or elaboration that utterly ignores the point made. I will do this so I can feel technically right, even if it means nothing and serves only to generate argumentation and/or confusion".

Quote:
None of which is the point.
Of course it's the point. The point, in case you missed because you took the time to snip it out of other posts, is that a single observer only experiences time one way. A second is a second. Another high velocity observer, due to the distance at which they would be moving apart, cannot meaningfully interact with the first to perceive the relative temporal distortion.

Quote:
The question in the OP was "Is violating causality via FTL really a problem? Can someone explain?" As that's about observers in relative motion we have scenarios where the observers are moving (in respect to each other) in one way.
...and magic phones or teleportation or something had to get interjected because, as I am speculating, those separate realities are stonewalled, and cannot meaningfully interact. The argument against this is that they can unmeaningfully interact. Kind of. If you squint and look at it a certain way.

This is like a physicist claiming we mostly don't exist physically, because it is mostly empty space between our atoms' nuclei and electrons. That's only true in a completely useless word-game sense, and highly counterproductive to gaining a conceptually simple, working model of what we are talking about.

Quote:
Sure, you couldn't really "pass the salt" (or go that fast through an atmosphere without turning the living room into ash) but the OP question wasn't about salt passing.
My example was. The OP question is directly related to the identical proposition: I don't think realities experiencing time differently can meaningfully interact. Certainly not with magical information transfer. The need to interject magic is exactly where the roadblock lies.

Quote:
You've previously accepted made-up numbers in the examples, and not worried (for example) exactly how Alice and Bob boil eggs in weightlessness (I'll now suggest centrifuges, so they can use regular kitchen equipment); why complain about this hypothetical?
There is a huge difference between using made up numbers and boiled eggs when they don't interfere with the hypothetical, versus playing a word game which does interfere with its construction.
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Old 25th November 2022, 11:15 AM   #141
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What's happening is you are dodging the actual explanations of the OP question, and trying to re-frame it all to your own preconceived ideas.

(ETA: To a certain extent, the OP content did that too, which is why it was largely ignored by everyone.)
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Old 25th November 2022, 11:25 AM   #142
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Originally Posted by Thermal View Post
... Of course it's the point. The point, in case you missed because you took the time to snip it out of other posts, is that a single observer only experiences time one way. A second is a second. Another high velocity observer, due to the distance at which they would be moving apart, cannot meaningfully interact with the first to perceive the relative temporal distortion.
No.

For the seventh time, it's not about the distance, it's that the distance is changing.

The voyager probe is moving quite fast* (as seen by Earth), so there will be some time dilation, but we still received meaningful data.

(ETA: * not that the specific speed matters, any difference does mean time dilation.)

Originally Posted by Thermal View Post
... and magic phones or teleportation or something had to get interjected because, ...
The OP question was about "FTL". That is why "magic phones or teleportation" get involved, not "interjected".

Originally Posted by Thermal View Post
... as I am speculating, those separate realities are stonewalled, and cannot meaningfully interact. The argument against this is that they can unmeaningfully interact. Kind of. If you squint and look at it a certain way. ...
Right, you are speculating your own opinions, not trying to learn what over a hundred years of physics has shown.

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Old 25th November 2022, 11:44 AM   #143
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Originally Posted by pzkpfw View Post
What's happening is you are dodging the actual explanations of the OP question, and trying to re-frame it all to your own preconceived ideas.
Well Jesus Christ, how many times do I have to repeat that? I am explaining in a variety of different ways where I am having a roadblock with the explanations. The explanations basically say "so if we didn't have this problem, this is what the problem would be like". That is not very illustrative, and certainly not clarifying anything.

Quote:
(ETA: To a certain extent, the OP content did that too, which is why it was largely ignored by everyone.)
Ignoring it would be the most intellectually cowardly approach.

The OP (who is no dummy) quite humbly ELI5s a tricky question. No pretense at all.

My ALI5 (answering like I'm 5) response is that moving between relative realities is in fact time travel with a new haircut, just traveling to a "location" where the cause had not happened yet. Effectively, that is either the past, or a reference frame where the event is meaningless to the first reference frame.
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Old 25th November 2022, 12:16 PM   #144
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Originally Posted by pzkpfw View Post
No.

For the seventh time, it's not about the distance, it's that the distance is changing.
Yeah, and I understood that the first six times too. When I occasionally shorthand to saying just the distance (when in the same paragraph I would have it fleshed out to something like "moving away at a high velocity creating a vast distance", I'd assume I wouldn't have to spell it out every time in a casual discussion. My bad.

Quote:
Right, you are speculating your own opinions, not trying to learn what over a hundred years of physics has shown.
Yeah, we're not getting anywhere here. You are unwilling or unable to deviate from your script. The problems I'm having aren't covered on your script, so this probably isn't the place I'll get them cleared up. One of these days I'll either find the right words to spell out my problem, or someone will recognize it and deliver that penny-drop explanation. It's not fair to keep dumping that here, though. Thanks, and see ya on the next one.
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Old 25th November 2022, 01:06 PM   #145
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Originally Posted by Thermal View Post
Yeah, and I understood that the first six times too. When I occasionally shorthand to saying just the distance (when in the same paragraph I would have it fleshed out to something like "moving away at a high velocity creating a vast distance", I'd assume I wouldn't have to spell it out every time in a casual discussion. My bad.
There's a great example.

In the one paragraph you say "and I understood that the first six times too"

Then you say "... creating a vast distance".

You contradict yourself!



(ETA "moving away" is wrong too. ETA2: "high velocity" too.)

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Old 25th November 2022, 08:53 PM   #146
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Originally Posted by Thermal View Post
Pretty sure we couldn't sit with them. Pretty sure that would have to be flying through the room at near lightspeed.
Yes, for half speed time they would be moving 0.886 c or so relative to you.

As I said, very briefly. For the purposes of answering the OP that's all you need.

But the point is that people right next to us have time running at a different speed to us, even moving at low speeds WRT us. .It is an everyday part of how the universe around us works, not some theoretical detail that only applies to people fat from each other.

Last edited by Robin; 25th November 2022 at 09:02 PM.
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Old 25th November 2022, 08:59 PM   #147
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Actually this is one of those rare threads where the question posed has a clear and straight forward answer.

FTL would involve time paradoxes and these can be demonstrated by mathematics and diagrams.

If we reject time travel we also are rejecting FTL travel. If we reject the possibility of time loop wormholes then we are basically rejecting that wormholes can be a thing at all.
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Old 25th November 2022, 09:49 PM   #148
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Originally Posted by Robin View Post
Yes, for half speed time they would be moving 0.886 c or so relative to you.

As I said, very briefly. For the purposes of answering the OP that's all you need.
The question was "can you sit with somone in your living room whose time is moving at half yours". Sitting with someone unequivocally means to be at rest. It does not mean moving apart at near lightspeed. There is no "very brief time" on the table to have both at rest, and simultaneously moving apart at .886c. Not a picosecond.

The answer to that question is an unequivocal "no", if we are entertaining the flimsiest of acquaintances with honesty.

Quote:
But the point is that people right next to us have time running at a different speed to us, even moving at low speeds WRT us. .It is an everyday part of how the universe around us works, not some theoretical detail that only applies to people fat from each other.
Yes. I know. We all know. Even the physicist who says we are mostly "not here" knows. If I slowly moonwalk away from my sleeping dog, I am experiencing time at an utterly insignificantly slower speed relative to her. It simply doesn't mean anything, and unquestionably evades the question I asked.

Eta: belongs in the Perpetual Weight Loss thread.
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