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Old 17th November 2022, 05:02 AM   #41
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Originally Posted by theprestige View Post
Yes, and also what breaking causality would actually look like in practice.
As I said, there is nothing that it would look like because it can't happen.

It's like asking what a broken unbreakable object would look like or a lifted unliftable stone.
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Old 17th November 2022, 05:34 AM   #42
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Originally Posted by William Parcher View Post
Would you be able to win the lottery with this?

After a lottery drawing you send the winning numbers to a distant spaceship at FTL. Then they send them back to you at FTL. The winning numbers arrive before the drawing and you play them for the win.

Is that one of the time travel paradoxes?
If you could afford to do that, you wouldn’t need to win the lottery.
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Old 17th November 2022, 05:56 AM   #43
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Originally Posted by Thermal View Post
1. A thing happens at 1:00.. Using the magic instantaneous phone, theprestige calls his buddies on Alpha Centauri to tell them the thing happened. The light has not reached AC to let them see this event has taken place.
That isn't the scenario.

Merely sending something to a place where the light hasn't reached yet wouldn't cause any paradox and no-one has claimed that it would.

OTOH if you have a magic telephone and send a message faster than the speed of light to someone travelling at a significantly different velocity to you and they have the same magic telephone to return the message then they would be able to get the message back to you before it was sent.

The point is that there are no magic telephones that can send messages faster than the speed of light and there never el be and so we will never see replies coming back before the message was sent.
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Old 17th November 2022, 06:28 AM   #44
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Originally Posted by Thermal View Post
Which is the calendar problem again. As soon as you draw a timeline, or calendar, or any other spacetime grid to represent the past and present existing at the 'same time', you have screwed the proverbial pooch, logistically.
Which is why no-,one has done that or anything even remotely like it.

A space time diagram shows past and present at different times,

Quote:
Yet if you place a pawn on today on this calendar, you can't slide it to last week and declare "Therefore, Time Travel! It is proven via the Supermodel of time which has no competition!" The model, indisputably powerhouse that it may be, does not reflect reality.
Which is why,; again, no-one has said that or anything like it.

Now let's set aside your straw men and look at what you can do.

You can use a space time diagram and the mathematics of special relativity and.show that if you could do impassible thing A (send messages at faster than the speed of light) then you would necessarily be able to do impossible thing B (send messages back in time).

Which demonstrates that there would indeed be causality violations if something could travel faster than light.

Last edited by zooterkin; 17th November 2022 at 10:00 AM. Reason: Broken quote
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Old 17th November 2022, 08:09 AM   #45
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Originally Posted by Olmstead View Post
Attempts at simple representation will always have their issues. There really isn't a debate here. Physicists in relevant fields agree that FTL messages, especially magical instantenous phones, would lead to time paradoxes if they were possible. A layman like myself isn't going to be able to poke holes into something they have been studying for decades. At that point, all I can do is to accept it and to try to wrap my head around the concepts as much as possible.
Yeah, I am too. I'm not saying that they are wrong. I have no doubt that they are much farther along in understanding than I could ever be. But in order to get even the loosest grasp, I'm looking for a comprehensible model. Simply baking in the calendar thing to the explanation kind of blows it for me.

For instance, when you said:

Originally Posted by Olmstead View Post
If TP and AC are travelling at different velocities, TP would receive the call from AC before 1:01.
...that didn't say anything to me. If my frame of reference was that of an observer hanging out in space able to see both parties, I would see AC experiencing time at a much different rate than (say) the much faster TP. So there would be weird time dialations in the exchange of information. Great.

But as TP and AC whiz along on their respective velocities, there is a line behind each of them called "the past", which has an asterisk beside it saying "for reference only". It is not actually there anymore.

Then the spacetime diagram casually shows an arrow capriciously crossing that line. That's where I hit full stop. It would...I don't know how it would be represented...'ricochet' off its course, not continue into the past which, by definition, isn't there anymore.

I am by no means suggesting they are wrong. I am saying the core problem is baked into the explanation, so it doesn't clarify anything to a layperson.
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Old 17th November 2022, 08:24 AM   #46
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Originally Posted by Robin View Post
You can use a space time diagram and the mathematics of special relativity and.show that if you could do impassible thing A (send messages at faster than the speed of light) then you would necessarily be able to do impossible thing B (send messages back in time).

Which demonstrates that there would indeed be causality violations if something could travel faster than light.
That's why I'm not really understanding theprestige's dilemma. It boils down to "if you could go back in time, why would you have a causal violation?" You would have one by definition, I would think. All the speculations along that line hard-wire in the impossible notion that the past continues to exist as a "place that could be traveled to".

If you entertain the Impossible Notion in any way, even theoretically, then time travel and all the paradoxes are right on the table. You are in science-fiction world, and I don't see why any problems would exist. You just 'impossible' them away. Why not, if the most foundational issue is being 'impossibled' away? Of course you will come up with impossible conundrums if you start with an Impossible Notion, no?
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Old 17th November 2022, 12:42 PM   #47
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Originally Posted by Thermal View Post
...that didn't say anything to me. If my frame of reference was that of an observer hanging out in space able to see both parties, I would see AC experiencing time at a much different rate than (say) the much faster TP. So there would be weird time dialations in the exchange of information. Great.

But as TP and AC whiz along on their respective velocities, there is a line behind each of them called "the past", which has an asterisk beside it saying "for reference only". It is not actually there anymore.

Then the spacetime diagram casually shows an arrow capriciously crossing that line. That's where I hit full stop. It would...I don't know how it would be represented...'ricochet' off its course, not continue into the past which, by definition, isn't there anymore.

I am by no means suggesting they are wrong. I am saying the core problem is baked into the explanation, so it doesn't clarify anything to a layperson.
See, from what I understand, the past of Person A can very literally still be there for someone with a different velocity (Person B). If two boxes explode at the same time for Person A, they won't explode at the same time for Person B. This isn't a perception thing. The order of events will literally be different. This is where the mind screw begins. A box will have exploded for one person, but won't have exploded for another person. The past of one person will still be there for another person.

The same would apply to your observer hanging out in space. They couldn't observe some universal line, because there isn't any.

Last edited by Olmstead; 17th November 2022 at 12:44 PM.
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Old 17th November 2022, 12:48 PM   #48
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Originally Posted by Olmstead View Post
See, from what I understand, the past of Person A can very literally still be there for someone with a different velocity (Person B). If two boxes explode at the same time for Person A, they won't explode at the same time for Person B. This isn't a perception thing. The order of events will literally be different. This is where the mind screw begins. A box will have exploded for one person, but won't have exploded for another person. The past of one person will still be there for another person.

The same would apply to your observer hanging out in space. They couldn't observe some universal line, because there isn't any.
Right, but in the their relative pasts and futures, right? They don't experience them from an 'objective' reference frame, so there would never be a point where one could look at the future, say, by looking over at anothers viewpoint?

eta: TL;DR: could they both observe the same box at the 'same time'? Seems their velocities would prohibit that, putting them each in their own isolated reference frame?
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Old 17th November 2022, 01:37 PM   #49
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I found this to be illuminating. The article's point of view is how trying to introduce relativity into space simulation gaming can break the game, but in a very meaningful way it can explain the real life problems inherent in FTL travel or communication. In the example, substitute Adama's peeking at Vader's computer with some hypothetical anomalous method of FTL signaling, because it amounts to exactly the same problem.

A Relatively Hard Game, by Kevin Lin

Quote:
Three players are playing a recreation of the famous battle in which the Battlestar Galactica and the Enterprise team up against the Death Star (shown above, not to scale) using the Space Battle Simulator 2000.
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Old 17th November 2022, 03:53 PM   #50
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Originally Posted by gnome View Post
I found this to be illuminating. The article's point of view is how trying to introduce relativity into space simulation gaming can break the game, but in a very meaningful way it can explain the real life problems inherent in FTL travel or communication. In the example, substitute Adama's peeking at Vader's computer with some hypothetical anomalous method of FTL signaling, because it amounts to exactly the same problem.

A Relatively Hard Game, by Kevin Lin
A worse problem is that Kirk, having seen the Galactica destroyed, can signal the USS Intrepid which is closing on the Death Star at warp speed and the Intrepid can destroy the Death Star before it has had.a chance to fire the laser blast that destroyed the Galactica.

So now the players have to decide which of the Death Star or the Galactica were destroyed.
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Old 17th November 2022, 05:48 PM   #51
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Originally Posted by Thermal View Post
Right, but in the their relative pasts and futures, right? They don't experience them from an 'objective' reference frame, so there would never be a point where one could look at the future, say, by looking over at anothers viewpoint?

eta: TL;DR: could they both observe the same box at the 'same time'? Seems their velocities would prohibit that, putting them each in their own isolated reference frame?
Just to set some ground rules, do you accept:
  1. That when two observers are in relative motion (not at rest with respect to each other), they can both consider themselves as at rest, and that the other is moving.
  2. That the speed of light is the same for every observer.
  3. That both of their clocks run "normally" according to themselves, but (because of 2) according to each, the others clock runs slow.

(If you don't it'd be good to clear that up first.)

Alice and Bob are in spaceships. Alice and Bob can both use a 3 minute egg timer to boil an egg, and for both of them it's perfect.

But, the distance between them is changing. Because of 2. and 3., they both know that time for the other is slow.

Bob knows that Alice's timer would have said 3 minutes when her egg was done, but his timer would have said 4 minutes.
Alice knows that Bob's timer would have said 3 minutes when his egg was done, but according to her timer it took 4 minutes.

(Made up numbers, the specific math isn't the point here. The main thing, is time dilation is as real as anything. Note also none of this is about when they see each others actions. They can be comparing video tapes next week at the bar.)

What if they used some method to start their timers at the same time. (Like, when their paths crossed and their solar panels touched.) That means when "now" was 3 minutes for Alice (her egg done), it was 2 minutes for Bob (his egg not yet done). And when "now" was 3 minutes for Bob (egg done), it was 2 minutes for Alice (egg not yet done).

(And further, when Bob's timer said 2, according to Bob's "now", Alice's timer said 1.)

Note that nothing is "going to the past here". It's really just that the idea of "now" gets very tricky, and especially: there is no universal "now" that will apply to everything at once. (There could be a Craig, Debbie, Edgar and more also in spaceships all doing different speeds. All of their clocks (time) at all sorts of rates vs each other.)

Putting it together, Alice at 3 (according to her timer) instantly says "my egg is done" to Bob. Bob gets the message at 2 (on his timer), and instantly replies "that's nice". Alice gets that reply at 1 (on her timer) ... before she sent her message.

Clearly weird, but it's not relativity that's wrong here, it's the idea that any message can be sent "instantly".

For any message sent < c from Alice to Bob, a reply that travels < c, will reach Alice after she sent the message.
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Old 17th November 2022, 09:06 PM   #52
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Originally Posted by pzkpfw View Post
Just to set some ground rules, do you accept:
  1. That when two observers are in relative motion (not at rest with respect to each other), they can both consider themselves as at rest, and that the other is moving.
  2. That the speed of light is the same for every observer.
  3. That both of their clocks run "normally" according to themselves, but (because of 2) according to each, the others clock runs slow.

(If you don't it'd be good to clear that up first.)

Yes, I get basic relativity (although I can see by my garbled posts above why you'd think I didn't. Pro tip:don't try to tape your fingers back together while considering time dilation. It's distracting as hell).

Quote:
Alice and Bob are in spaceships. Alice and Bob can both use a 3 minute egg timer to boil an egg, and for both of them it's perfect.

But, the distance between them is changing. Because of 2. and 3., they both know that time for the other is slow.

Bob knows that Alice's timer would have said 3 minutes when her egg was done, but his timer would have said 4 minutes.
Alice knows that Bob's timer would have said 3 minutes when his egg was done, but according to her timer it took 4 minutes.

(Made up numbers, the specific math isn't the point here. The main thing, is time dilation is as real as anything. Note also none of this is about when they see each others actions. They can be comparing video tapes next week at the bar.)

What if they used some method to start their timers at the same time. (Like, when their paths crossed and their solar panels touched.) That means when "now" was 3 minutes for Alice (her egg done), it was 2 minutes for Bob (his egg not yet done). And when "now" was 3 minutes for Bob (egg done), it was 2 minutes for Alice (egg not yet done).

(And further, when Bob's timer said 2, according to Bob's "now", Alice's timer said 1.)

Note that nothing is "going to the past here". It's really just that the idea of "now" gets very tricky, and especially: there is no universal "now" that will apply to everything at once. (There could be a Craig, Debbie, Edgar and more also in spaceships all doing different speeds. All of their clocks (time) at all sorts of rates vs each other.)

Putting it together, Alice at 3 (according to her timer) instantly says "my egg is done" to Bob. Bob gets the message at 2 (on his timer), and instantly replies "that's nice". Alice gets that reply at 1 (on her timer) ... before she sent her message.

Clearly weird, but it's not relativity that's wrong here, it's the idea that any message can be sent "instantly".

For any message sent < c from Alice to Bob, a reply that travels < c, will reach Alice after she sent the message.
Ok. I would see the messages being received differently. Like so:

-Alice and Bob each see the other's clock as running slower, if they consider themselves 'normal' and the other zipping away from them at high speed.

=Alice's timer hits 3, and she sends the magic IM to Bob that her egg is done.

-Bob sees her timer as still being back at 1 when he gets the message, and marvels at the weirdness of temporal information distortion at these speeds. After all, he knows full and well from the IM that what he is perceiving about her clock is not 'real', as proven by the IM, which indicates she is really at 3.

-He sends the return "that's nice" IM when he perceives Alice's clock as being at two, but Alice's clock receives this when her own timer now reads four. It only reads 2 from Bob's dilated perspective.
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Old 17th November 2022, 09:24 PM   #53
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No. You are skipping over the real life effects of each persons clock being normal and the others being slow.

Originally Posted by Thermal View Post
...
Ok. I would see the messages being received differently. Like so:

-Alice and Bob each see the other's clock as running slower, if they consider themselves 'normal' and the other zipping away from them at high speed.
Fine enough so far.

Originally Posted by Thermal View Post
=Alice's timer hits 3, and she sends the magic IM to Bob that her egg is done.
At 3 "now" for Alice, what time is it for Bob? Bob's time is running slow (according to Alice) so his timer will be less than 3. This is not a visual artifact, it's reality for Alice.

Originally Posted by Thermal View Post
-Bob sees her timer as still being back at 1 when he gets the message, ...
When he gets that "instant" message, Alice's timer was at 3 (imagine her message is a picture of her timer and that nice egg).

His timer is less than 3 when he gets the message. (And as below, at that point her timer is less than his too - but easiest to think one step at a time.)

Originally Posted by Thermal View Post
...and marvels at the weirdness of temporal information distortion at these speeds. After all, he knows full and well from the IM that what he is perceiving about her clock is not 'real', as proven by the IM, which indicates she is really at 3.
At 2 "now" for Bob, what time is it for Alice? Alice's time is running slow (according to Bob) so her timer will be less than 2. This is not a visual artifact, it's reality for Bob.

Be careful with that word "really". That smells of absolutism. Relativity showed us time, distance, simultaneity are not absolute - but it can be hard to stop assuming they are. What's "really"? For whom?

Originally Posted by Thermal View Post
-He sends the return "that's nice" IM when he perceives Alice's clock as being at two, but Alice's clock receives this when her own timer now reads four. It only reads 2 from Bob's dilated perspective.
Alice can't receive the message at 4, and her timer can't read both 2 and 4 at the same time.

At 2 on Bob's timer, from Bob's reality Alice's timer is at 1, not 4.

I think this comes from that "really". You are assuming Alice's' clock will "really" be at 4 when Bob considers it to be 1.

Why is Alice's time "real" but Bob's time is not? You are placing an absolute time and "now" on the Universe and assume Alice is on it and Bob is not.



(It's 5:24 pm on a hot day at the end of the week. I have had a beer waiting for the cricket, sorry if I go astray.)

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Old 17th November 2022, 09:41 PM   #54
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Ok, let's simplify a little further, then everything should follow from there:

-Alice and Bob are zipping away from each other. Each sees the other's clock as running slower, yes?

-Alice's timer reads 3, when she sees Bob's timer as reading one. At the same time, Bob sees his timer as reading 3, and sees Alice's as reading 1. Do I have this right?

-so when Alice's first IM goes through, it is 3 on her timer, but Bob sees her timer as being on 1. When Bob sends the reply IM, he sees Alice's timer as being on 2...but Alice sees her own timer as being on 4.
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Old 17th November 2022, 10:09 PM   #55
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Originally Posted by Thermal View Post
Ok, let's simplify a little further, then everything should follow from there:

-Alice and Bob are zipping away from each other. Each sees the other's clock as running slower, yes?
Yes.

Originally Posted by Thermal View Post
-Alice's timer reads 3, when she sees Bob's timer as reading one. At the same time, Bob sees his timer as reading 3, and sees Alice's as reading 1. Do I have this right?
Sort of. Each half is accurate enough (I was using 2 not 1 here, which I'll go back to ...) but sticking "at the same time" in there muddies the waters.

3 for Alice is 2 for Bob.
3 for Bob is 2 for Alice.

But Alice can't be looking at her own timer and see both 3 and 2.
And Bob can't be looking at his own timer and see both 3 and 2.

Originally Posted by Thermal View Post
-so when Alice's first IM goes through, it is 3 on her timer, but Bob sees her timer as being on 1. When Bob sends the reply IM, he sees Alice's timer as being on 2...but Alice sees her own timer as being on 4.
You have Bob seeing both 1 and 2 on Alice's timer. That doesn't make sense. And I think you are still applying an absolute view on things (where Alice is the one who is "right").

From the first part of this post:

(A) 3 for Alice is 2 for Bob.
(B) 3 for Bob is 2 for Alice.

Extrapolate that back:

(C) 2 for Alice is 1 for Bob.
(D) 2 for Bob is 1 for Alice.

Alice sending her magic message is (A), Bob's magic reply is (D). Alice gets the magic reply at 1, not 4.

(D) is not Bob being tricked by an illusion that Alice is 1 when she's "really" 4.

(You might complain that 2 for Bob is two different values for Alice, but note that (A) is Alice's reality and (D) is Bob's reality. Remember the first line of this post "Each sees the other's clock as running slower, yes?". In (A) Bob can calculate that Alice was at 3, but for his "now" (D) is in effect.)


ETA: maybe it would help to just completely forget (A) for a moment. Given all the standard setup including the synchronised timers, and your agreement that the "other persons" clock is slower, Bobs send a magic message to Alice at 2 on his timer. What will Alice see on her timer when she gets that message? Why would it be 4?

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Old 18th November 2022, 05:57 AM   #56
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Extrapolating from the prior example, if Bob sends the magic message to Alice when it is 2 on his timer then it will be 6 on Alice's timer when she receives it.
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Old 18th November 2022, 08:28 AM   #57
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Originally Posted by pzkpfw View Post
Yes.



Sort of. Each half is accurate enough (I was using 2 not 1 here, which I'll go back to ...) but sticking "at the same time" in there muddies the waters.

3 for Alice is 2 for Bob.
3 for Bob is 2 for Alice.

But Alice can't be looking at her own timer and see both 3 and 2.
And Bob can't be looking at his own timer and see both 3 and 2.



You have Bob seeing both 1 and 2 on Alice's timer. That doesn't make sense. And I think you are still applying an absolute view on things (where Alice is the one who is "right").
Not really. I am acknowledging that "time marches on". By having events happening, messages sent, and replies made all when the timer is reading 1, I think we are causing needless confusion. Bob's reply took a moment to compose and feed into the IM machine, and by the time he did that, another 'minute' would have ticked by on their respective timers.

Quote:
From the first part of this post:

(A) 3 for Alice is 2 for Bob.
(B) 3 for Bob is 2 for Alice.

Extrapolate that back:

(C) 2 for Alice is 1 for Bob.
(D) 2 for Bob is 1 for Alice.

Alice sending her magic message is (A), Bob's magic reply is (D). Alice gets the magic reply at 1, not 4.

(D) is not Bob being tricked by an illusion that Alice is 1 when she's "really" 4.

(You might complain that 2 for Bob is two different values for Alice, but note that (A) is Alice's reality and (D) is Bob's reality. Remember the first line of this post "Each sees the other's clock as running slower, yes?". In (A) Bob can calculate that Alice was at 3, but for his "now" (D) is in effect.)


ETA: maybe it would help to just completely forget (A) for a moment. Given all the standard setup including the synchronised timers, and your agreement that the "other persons" clock is slower, Bobs send a magic message to Alice at 2 on his timer. What will Alice see on her timer when she gets that message? Why would it be 4?
Ok. You are rightly criticizing my falling back on 'real' time. Let's apply the usual 'meeting at the bar to compare tapes after the flight' scenario.

-Thermal is on earth as the 'neutral' Mission Control for Operation MEBE (Most Expensive Breakfast Ever). MEBE will run for 10 minutes, Earth referential frame time.

-Astronauts Alice and Bob take off in opposite directions at whatever velocity, say c/2 (I think we skipped over the opposite thing, before: if they were holding hands going in the same direction, they would not experience any of this).

-Upon landing, we all go to the bar, wearing horn-rimmed glasses and smoking, if I remember Space Program fashion. Thermal previously put a couple of those snazzy Ring cameras in each of A & B''s ships. Let's compare the video.

-Thermal clocks the mission at 10 minutes. Alice and Bob have the mission clocked at say 8 minutes on their timers. When we roll the video, we see both Alice and Bob moving slower as their speed increases, and their clocks ran slower. They experienced time and movement as normal.

-What else would we expect to see on the 10 minute side by side comparative footage? Would we expect to see Alice's timer being at three, when Bob's was at two, when at the same time Bob's read three and Alice's read two? That is a flat-out impossible contradiction.
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Old 18th November 2022, 10:02 AM   #58
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Originally Posted by Thermal View Post
-What else would we expect to see on the 10 minute side by side comparative footage? Would we expect to see Alice's timer being at three, when Bob's was at two, when at the same time Bob's read three and Alice's read two? That is a flat-out impossible contradiction.
But since the scenario is based on the assumption that they can do an impossible thing (ie communicate with each other instantaneously) then it isn't surprising that it leads to a contradiction.

The key is that Bob's "now" isn't the same as Alice's "now"
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Old 18th November 2022, 10:14 AM   #59
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Originally Posted by Robin View Post
But since the scenario is based on the assumption that they can do an impossible thing (ie communicate with each other instantaneously) then it isn't surprising that it leads to a contradiction.

The key is that Bob's "now" isn't the same as Alice's "now"
Right, and I get that, but where I am floundering is where their respective 'nows' would be anything other than a warped relativistic perception. That's what a timestamped video should straighten out, to provide a simulated instantaneous communication across massive distances. It would reconstruct it tail end.

So what would the videos show, played side-by-side, with no need to calculate the time on the other's timer, or needing magic instantaneous phones?
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Old 18th November 2022, 10:54 AM   #60
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you are all forgetting:

Quote:
"No matter how fast the body travels, the soul only travels at the speed of an Arcturan Mega-Donkey"
- OOlan Colluphid
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Old 18th November 2022, 02:00 PM   #61
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Originally Posted by Thermal View Post
Not really. I am acknowledging that "time marches on". By having events happening, messages sent, and replies made all when the timer is reading 1, I think we are causing needless confusion. Bob's reply took a moment to compose and feed into the IM machine, and by the time he did that, another 'minute' would have ticked by on their respective timers.
Sure, "time marches on", and for any message/reply both sent at c or less, the reply is received after the message is sent.

But even (yes the specific numbers are made up) if Bob takes 1 minute to compose his mreply, in this scenario Alice still receives it before she sent the message.

We need the numbers to help stop it all just being words that mean what we want them to mean, to illustrate what relativity tells us, and to highlight that "now" for each is different.

Originally Posted by Thermal View Post
Ok. You are rightly criticizing my falling back on 'real' time. Let's apply the usual 'meeting at the bar to compare tapes after the flight' scenario.

-Thermal is on earth as the 'neutral' Mission Control for Operation MEBE (Most Expensive Breakfast Ever). MEBE will run for 10 minutes, Earth referential frame time.

-Astronauts Alice and Bob take off in opposite directions at whatever velocity, say c/2 (I think we skipped over the opposite thing, before: if they were holding hands going in the same direction, they would not experience any of this).
They don't need to be going in opposite directions, and this wasn't skipped. In earlier posts I've mentioned "when two observers are in relative motion (not at rest with respect to each other)", and "But, the distance between them is changing"

Originally Posted by Thermal View Post
-Upon landing, we all go to the bar, wearing horn-rimmed glasses and smoking, if I remember Space Program fashion. Thermal previously put a couple of those snazzy Ring cameras in each of A & B''s ships. Let's compare the video.

-Thermal clocks the mission at 10 minutes. Alice and Bob have the mission clocked at say 8 minutes on their timers. When we roll the video, we see both Alice and Bob moving slower as their speed increases, and their clocks ran slower. They experienced time and movement as normal.

-What else would we expect to see on the 10 minute side by side comparative footage? Would we expect to see Alice's timer being at three, when Bob's was at two, when at the same time Bob's read three and Alice's read two? That is a flat-out impossible contradiction.
How do you make the footage "side by side" when time itself was different for them? Landing where? Together? If you are trying to record what they each see (vs know or calculate) of each other, how to you account for light speed delay in those observations? Details! ETA: the bit I bolded is also another indication of unconsciously imposing an absolute time or "now" on the Universe. The "contradictions" only arise when faster than c information travel is brought in to play. No one observer would actually see two different numbers on one clock (just for example).


In this new more complicated scenario, at 10 according to Thermal, the situation with Alice and Bob is symmetrical, let's say their timers are at 8 according to his "now".

But for Alice (considering herself at rest), Thermal is moving, and Bob is moving faster. So when her timer says 8, according to her "now" Thermals' is 6 and Bob's is 4.

And for Bob (considering himself at rest), Thermal is moving, and Alice is moving faster. So when his timer says 8, according to his "now" Thermals' is 6 and Alices's is 4.

This isn't wishful thinking, it's the result of relativity. Each observer (I'm ignoring acceleration here) is at rest and the other observers are moving, so their time is slower (by two different rates now).

You say "flat-out impossible contradiction" but - welcome to relativity, it's weird to creatures who live with mundane speed variations.

In post #51 I tried hard to lay it out in small steps. You may as well have stopped at:
"Bob knows that Alice's timer would have said 3 minutes when her egg was done, but his timer would have said 4 minutes.
Alice knows that Bob's timer would have said 3 minutes when his egg was done, but according to her timer it took 4 minutes." and said "no" then.

Last edited by pzkpfw; 18th November 2022 at 02:39 PM.
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Old 18th November 2022, 02:08 PM   #62
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Thermal, do you see this picture?
(Not really sure how image handling works here, and when I looked at an earlier post I stuck a picture in, from a different device, the image didn't show. Not sure if that's simply because I wasn't logged on, or what. Ignore the content, it's just a test.)


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Old 18th November 2022, 03:10 PM   #63
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I haven't been following... is this just the standard twin paradox being discussed?
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Old 18th November 2022, 03:12 PM   #64
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Originally Posted by Ziggurat View Post
I haven't been following... is this just the standard twin paradox being discussed?
No. Causality breaking by faster than light information.
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Old 18th November 2022, 03:43 PM   #65
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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.
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Old 18th November 2022, 05:28 PM   #66
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Originally Posted by Thermal View Post
Right, and I get that, but where I am floundering is where their respective 'nows' would be anything other than a warped relativistic perception. That's what a timestamped video should straighten out, to provide a simulated instantaneous communication across massive distances. It would reconstruct it tail end.

So what would the videos show, played side-by-side, with no need to calculate the time on the other's timer, or needing magic instantaneous phones?
How does that simulate communication across vast distances?

The way to do it is that there are a set of synchronised clocks and cameras which co move with Alice, each recording the time on Bob's clock and the time on their own.

This would show the times that would be showing if Alice had instantaneously viewed Bob's clock.

Similarly Bob has an array of synchronised clocks and cameras behind him comoving with him taking a picture of Alice's clock and their own clock. This would give the time that Bob would see if he instantaneously viewed Alice's clock

Afterwards they can bring all the videos together and superimpose the images on Alice's video at the matching timestamp and superimpose Bob's camera images with the matching timestamps, then run Alice's and Bob's videos side by side. What you would see is the clocks that are synchronised with Alice's clock would be ahead of Bob's clocks and the clocks synchronised with Bob's clocks would be ahead of Alice's clocks.

Last edited by Robin; 18th November 2022 at 05:39 PM.
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Old 18th November 2022, 05:54 PM   #67
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Or more simply, there is an array of synchronised clocks comoving with Alice and an array of synchronised clocks comoving with Bob.

So we have a video of Bob and his clocks and comparing it with the adjacent clock which is comoving with Alice.

And a video of Alice and her clock and comparing it with the adjacent clock comoving with Bob.

This will simulate reading time instantly across vast distances.

Now we run both videos side by side. So we see Bob:s clock is ahead of Alice's clocks as they appear in his videos and Alice's clock is ahead of Bob's clocks as they appear in her video..

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Old 18th November 2022, 09:48 PM   #68
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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.
That’s not quite true. You can allow FTL communication, and even FTL travel, without breaking causality IF you also create a preferred reference frame. Within this preferred frame, travel and communication can travel up to infinite speed, but never backwards in time. In other reference frames, you can only go backwards in time in one spatial direction, never the other, so that there’s no way to do a round trip to go back in time along your world line.

But this requires introducing new physics as well as breaking Lorenz invariance. Not logically impossible, but no evidence for it.
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Old 18th November 2022, 09:48 PM   #69
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Originally Posted by pzkpfw View Post
Sure, "time marches on", and for any message/reply both sent at c or less, the reply is received after the message is sent.

But even (yes the specific numbers are made up) if Bob takes 1 minute to compose his mreply, in this scenario Alice still receives it before she sent the message.

We need the numbers to help stop it all just being words that mean what we want them to mean, to illustrate what relativity tells us, and to highlight that "now" for each is different.



They don't need to be going in opposite directions, and this wasn't skipped. In earlier posts I've mentioned "when two observers are in relative motion (not at rest with respect to each other)", and "But, the distance between them is changing"



How do you make the footage "side by side" when time itself was different for them? Landing where? Together? If you are trying to record what they each see (vs know or calculate) of each other, how to you account for light speed delay in those observations? Details! ETA: the bit I bolded is also another indication of unconsciously imposing an absolute time or "now" on the Universe. The "contradictions" only arise when faster than c information travel is brought in to play. No one observer would actually see two different numbers on one clock (just for example).


In this new more complicated scenario, at 10 according to Thermal, the situation with Alice and Bob is symmetrical, let's say their timers are at 8 according to his "now".

But for Alice (considering herself at rest), Thermal is moving, and Bob is moving faster. So when her timer says 8, according to her "now" Thermals' is 6 and Bob's is 4.

And for Bob (considering himself at rest), Thermal is moving, and Alice is moving faster. So when his timer says 8, according to his "now" Thermals' is 6 and Alices's is 4.

This isn't wishful thinking, it's the result of relativity. Each observer (I'm ignoring acceleration here) is at rest and the other observers are moving, so their time is slower (by two different rates now).

You say "flat-out impossible contradiction" but - welcome to relativity, it's weird to creatures who live with mundane speed variations.

In post #51 I tried hard to lay it out in small steps. You may as well have stopped at:
"Bob knows that Alice's timer would have said 3 minutes when her egg was done, but his timer would have said 4 minutes.
Alice knows that Bob's timer would have said 3 minutes when his egg was done, but according to her timer it took 4 minutes." and said "no" then.
Ok, here's the thing. I'm not trying to follow along. That's easy. I'm trying to get a handle on what is really going on. The descriptions given translate to me as simply distortions in perception. I have been assured that they are not. So how do we demonstrate that they are not? The parallel video playback should show what is objectively happening and when (relative to each other), and without the need for miracle phones.

A & B are off and accelerating away from each other. A video counting off time is recording in each of their ships. Thermal has one running on the ground for reference. His involvement changes nothing, except to verify time dilation occurred in both ships (which we already knew would).

A & B return to earth, and play their respective videos side by side. The timers on their clocks should be in sync, from takeoff to landing, yes? They just wouldn't jibe with Thermal's. This is expected.

So we watch the videos. At Alice's minute 3, she would perceive Bob's clock at minute 2, yes? But the video would show both clocks at 3.

Do you see my hangup, here?
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Old 18th November 2022, 10:20 PM   #70
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Originally Posted by pzkpfw View Post
Thermal, do you see this picture?
(Not really sure how image handling works here, and when I looked at an earlier post I stuck a picture in, from a different device, the image didn't show. Not sure if that's simply because I wasn't logged on, or what. Ignore the content, it's just a test.)

http://www.internationalskeptics.com...ictureid=13240
Yep, test passed.
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Old 18th November 2022, 10:25 PM   #71
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Originally Posted by Thermal View Post
Ok, here's the thing. I'm not trying to follow along. That's easy. I'm trying to get a handle on what is really going on.
As soon as you say "what is really going on" you are (again) showing you disbelieve relativity. You may not realise it, but by looking for some single "god view" of "truth" you are looking for absolute time and absolute "now" - and for over a hundred years we've known these just don't exist.

Originally Posted by Thermal View Post
The descriptions given translate to me as simply distortions in perception. I have been assured that they are not. So how do we demonstrate that they are not? The parallel video playback should show what is objectively happening and when (relative to each other), and without the need for miracle phones.
The miracle phone is only there because people want "instant" communication (your "IM"), and that's only there to show what "now" is for one observer, translated to another.

The effects of relativity are not distortions. Alice and Bob have their own reality. There is not some other situation that's "real reality" against which both Alice and Bob are hallucinating.

Originally Posted by Thermal View Post
A & B are off and accelerating away from each other. A video counting off time is recording in each of their ships. Thermal has one running on the ground for reference. His involvement changes nothing, except to verify time dilation occurred in both ships (which we already knew would).

A & B return to earth, and play their respective videos side by side. The timers on their clocks should be in sync, from takeoff to landing, yes? They just wouldn't jibe with Thermal's. This is expected.
Assuming everything is symmetrical (A & B accelerated the same to leave, and come back) then A and B would have timers that match each other, and are both showing less time elapsed than Thermals timer. I don't see what the video has added here. (This is essentialy twins' paradox time, which adds a layer of complication I don't think should be added to this thread.)

Originally Posted by Thermal View Post
So we watch the videos. At Alice's minute 3, she would perceive Bob's clock at minute 2, yes?
There is a distance between Alice and Bob, so your video technique has to account for delay in light travel time (seeing each others clock).

Robin gave some good advice on how videos would really help, with vast arrays of clocks at rest with respect to each observer (and thus in motion relative to other obserevrs). This just isn't simple.

Originally Posted by Thermal View Post
But the video would show both clocks at 3.
Do you see my hangup, here?
Which video?

Sorry, but while you think you are simplifying things, this is all way too sloppy to use. You need to give WAY more detail on how to really set it all up, how they are watching each other, how they are accounting for light delays, how they manage the journeys.



As soon as Alice and Bob both correctly say "my clock is normal, yours is slow" - you are simply not going to get a single-one-"true"-view of the situation.

Last edited by pzkpfw; 18th November 2022 at 10:31 PM. Reason: typo
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Old 18th November 2022, 10:30 PM   #72
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Originally Posted by Thermal View Post
Yep, test passed.
Cool. Please tell me if there is anything you disagree with in the following.

(Disclaimer: this is no kind of "official" diagram, it's just my simple visualisation.)

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Old 18th November 2022, 10:56 PM   #73
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Originally Posted by pzkpfw View Post
Cool. Please tell me if there is anything you disagree with in the following.

(Disclaimer: this is no kind of "official" diagram, it's just my simple visualisation.)

http://www.internationalskeptics.com...ictureid=13243
Not much to disagree with. If I really wanted to be a prick, I could say that in #1, A & B could just as well say they are aware that they are moving on known trajectories and velocities, but I doubt that helps anything.
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Old 19th November 2022, 12:13 AM   #74
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Originally Posted by Thermal View Post
Not much to disagree with. If I really wanted to be a prick, I could say that in #1, A & B could just as well say they are aware that they are moving on known trajectories and velocities, but I doubt that helps anything.
Oh absolutely, there can be a third observer who says they are still and both Alice and Bob are moving. But you know that's not the point.

So, any issues with the next two pics?

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Old 19th November 2022, 01:11 AM   #75
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Originally Posted by Thermal View Post
Ok, here's the thing. I'm not trying to follow along. That's easy. I'm trying to get a handle on what is really going on. The descriptions given translate to me as simply distortions in perception. I have been assured that they are not. So how do we demonstrate that they are not? The parallel video playback should show what is objectively happening and when (relative to each other), and without the need for miracle phones.

A & B are off and accelerating away from each other. A video counting off time is recording in each of their ships. Thermal has one running on the ground for reference. His involvement changes nothing, except to verify time dilation occurred in both ships (which we already knew would).

A & B return to earth, and play their respective videos side by side. The timers on their clocks should be in sync, from takeoff to landing, yes? They just wouldn't jibe with Thermal's. This is expected.

So we watch the videos. At Alice's minute 3, she would perceive Bob's clock at minute 2, yes? But the video would show both clocks at 3.

Do you see my hangup, here?
The problem is, Alice's video was taken at 33 frames per Alice's seconds and Bob's video was taken at 33 frames per Bob's seconds.

Playing them side by side, therefore, can't tell you that Bob's seconds are the same length as Alice's seconds.

On the other hand the earlier example I gave of the arrays of comoving synchronised clocks will give you just exactly the times that Bob and Alice would read if they could instantaneously read each other's clocks.
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Old 19th November 2022, 12:42 PM   #76
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Originally Posted by pzkpfw View Post
Oh absolutely, there can be a third observer who says they are still and both Alice and Bob are moving. But you know that's not the point.
Not a third person- they themselves could factor in that they are moving away from each other, not themselves at rest and the other moving. Would that change their calculations about how time is being experienced?

But let's roll with the opening paradigm. A & B perceive themselves as stationary, and the other moving. We know that this is a distortion, so let's continue factoring that in:

Quote:
So, any issues with the next two pics?
Just the minor tweak that each perceives the other as moving in slower time.

If we don't like that particular monkey wrench, then we should adjust the opening gambit to each knowing they are not at rest, but in motion as well, and factor their own temporal distortion from their POV into the cake. It's easier than trying to correct it later.

Unless this all hinges on the mistaken perception that each is respectively at rest?

http://www.internationalskeptics.com...ictureid=13244[/quote]
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Old 19th November 2022, 01:00 PM   #77
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Originally Posted by Robin View Post
The problem is, Alice's video was taken at 33 frames per Alice's seconds and Bob's video was taken at 33 frames per Bob's seconds.

Playing them side by side, therefore, can't tell you that Bob's seconds are the same length as Alice's seconds.
And that's exactly my point. If A or B experienced time normally, and the videos showed it was passing normally (with the predictably shorter time dilation aside), then what difference would it make how the other's time looked from a distorted standpoint? From the internal and external vantage points, everything was copacetic. Temporarily mangling one perspective wouldn't affect that.

Btw, I want to reiterate: I am not arguing against you or pzkpfw. I am trying to show clearly where my roadblock is, and why I can't get around it.

Quote:
On the other hand the earlier example I gave of the arrays of comoving synchronised clocks will give you just exactly the times that Bob and Alice would read if they could instantaneously read each other's clocks.
I'm not sure what this array of clocks would be synchronized to. Each other? Seems redundant. Adjust one to the other travelers time and keep one at your own? That's only two. I guess they would read the same if we correct the perceptual distortion that either is at rest as compared to the other. Each clock in the array would run accounting for the dilation that Thermal sees relative to earth's time frame. Different results then, yes?
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Old 19th November 2022, 02:01 PM   #78
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Originally Posted by Thermal View Post
Not a third person- they themselves could factor in that they are moving away from each other, not themselves at rest and the other moving. Would that change their calculations about how time is being experienced?
What this is about is one of the basics of relativity: Physics works the same for any inertial (not accelerating) observer.

Specifically: Alice and Bob (whatever their constant speed compared to whatever else, e.g. Thermal) can do any experiment with pendulums, clocks, bunsen burners, and egg boiling ... and get the same results as each other, the same as if they are "still". Alice's egg takes 3 minutes to boil, according to her timer, whether she considers herself at rest, or 100 kph relative to Bob, or 2,000 kph relative to Thermal.

So no, that would not change their "calculations about how time is being experienced". (It might just make those calculations harder to do.)

(ETA: if Alice considers herself moving, for the purpose of all this, then knowing relativity she'd have to consider her own time must be going slower than what she considers she's moving relative to. She'd also have to readjust what she considers Bob's speed to be - no longer relative to her, but relative to what she considers she's moving relative to. That would all make her calculations much much harder to do. Way easier for her, knowing it doesn't make a difference to the outcome, to consider herself as at rest. (Same for Bob.))

Originally Posted by Thermal View Post
But let's roll with the opening paradigm. A & B perceive themselves as stationary, and the other moving. We know that this is a distortion, so let's continue factoring that in:
No, it's not a distortion, it's relativity. You are trying to impose an absolute truth on the scenario.

Originally Posted by Thermal View Post
Just the minor tweak that each perceives the other as moving in slower time.
No, it's not just "perception", it's relativity.
The speed of light has to be the same for everyone.
For Alice, Bob is moving. For the speed of light to be the same for him, his time changes. That's real, not just perception, for Alice.
For Bob, Alice is moving. For the speed of light to be the same for her, her time changes. That's real, not just perception, for Bob.
Again, you are looking for a single absolute truth in time. You are denying what relativity showed.

Originally Posted by Thermal View Post
If we don't like that particular monkey wrench, then we should adjust the opening gambit to each knowing they are not at rest, but in motion as well, and factor their own temporal distortion from their POV into the cake. It's easier than trying to correct it later.

Unless this all hinges on the mistaken perception that each is respectively at rest?
It's not a mistaken perception, it's the natural outcome of knowing that Physics works the same for any inertial (not accelerating) observer.

Last edited by pzkpfw; 19th November 2022 at 02:40 PM.
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Old 19th November 2022, 02:17 PM   #79
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Originally Posted by Thermal View Post
And that's exactly my point. If A or B experienced time normally, and the videos showed it was passing normally (with the predictably shorter time dilation aside), then what difference would it make how the other's time looked from a distorted standpoint? From the internal and external vantage points, everything was copacetic. Temporarily mangling one perspective wouldn't affect that.
Alice's video will show her own time passing normally (their own 3 minute timer makes a nice boiled egg).
Bob's video will show his time passing normally (their own 3 minute timer makes a nice boiled egg).
But due to the speed of light having to be the same for everyone, they simply can't "agree" ("see", "calculate", whatever ...) that the others' time is the same.
If their own video is recording their own timer, and via telescope the other's timer (or better (as there'd be no offset due to distance) as per Robin, an array of clocks at rest with the other) they will actually record the other clock going slower.

Ignore relativity for a moment:

Alice is standing still, and is facing Carol (also standing still), who throws a ball at her, at 10 kph relative to the ground.
The ball hits Alice at 10 kph.
Bob is running towards Carol, at 10 kph. He (ignoring relativity) gets hit with a ball at 20 kph relative to his face.

That's not how light "works".

If Carol is shing a torch at Alice, the light is hitting Alice's face at c.
Bob is running towards Carol, at 10 kph. He does not get hit with light going c + (10 kph).
Light still hits him at c (he and Alice agree on this). His own 10 kph (according to Alice) gets factored out by his time (according to Alice) being slower.

Originally Posted by Thermal View Post
Btw, I want to reiterate: I am not arguing against you or pzkpfw. I am trying to show clearly where my roadblock is, and why I can't get around it.
All good. I'm not (yet! ;-) ) thinking of you as like someone who thinks covid vaccines are full of tracking chips.

Originally Posted by Thermal View Post
I'm not sure what this array of clocks would be synchronized to. Each other? Seems redundant. Adjust one to the other travelers time and keep one at your own? That's only two. I guess they would read the same if we correct the perceptual distortion that either is at rest as compared to the other. Each clock in the array would run accounting for the dilation that Thermal sees relative to earth's time frame. Different results then, yes?
The point of the array of clocks is it helps an observer "know" or "see" what time is for the other observer - without any delay because one of the clocks is always close by. Note that you need an array of clocks for every observer you consider moving, as their clocks need to be at rest according to them (if they were not at rest, their time would be slower).

So there's a million clocks all over the place, at rest with Bob, so their time is ticking at the same speed as him.
And there's a million clocks all over the place, at rest with Alice, so their time is ticking at the same speed as her.
(The Alice clocks are not at rest with respect to the Bob clocks.)
So when Alice videos her own timer, out her window she has a very close clock passing by showing Bob's time (which will be slower).
And when Bob videos his own timer, out his window he has a very close clock passing by showing Alice's time (which will be slower).

Last edited by pzkpfw; 19th November 2022 at 02:45 PM.
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Old 19th November 2022, 02:18 PM   #80
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(I won't add pics 5 and 6 yet.)
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