Is FTL actually possible?

[swansont]

3 hours ago, MJ kihara said:

Am trying to think about neutrino...it doesn't recognize a nutshell....can you hold it.is it physical?

I said “in principle”

[Moontanman]

11 hours ago, swansont said:

You could draw the lines in his diagram for a FTL ship. Depending on the speed of the ship (it's not instantaneous in his example; that would be a horizontal line) you could have a violation or not, depending on the speed.  But you had said it was instantaneous, and if you drew the lines, you would get a causality violation for a finite speed FTL ship 

 

If you can put it in a nutshell and hand it to me (in principle) it's a physical thing.

So instantaneous is ok as long as it doesn't come from a moving ship? That is what I thought.  

[Genady]

14 hours ago, Moontanman said:

It seems (to me at least) to be saying that a causality violation only occurs if a FTL transmission goes from the STL ship to Earth.

In his scenario, yes, the FTL transmission goes from STL ship to Earth. But this is not necessary. The paradox can be demonstrated also without such transmission.

Instead, assume that there is a "train" of STL ships with synchronized clocks between all the "cars" (ships.) The "conductor" of the train made an arrangement that whatever ship passes the Earth at 9h, blows off the FTL transmitter on Earth.

To be specific, let's say that the train moves with 3/5 speed of light. This speed makes a relativistic time dilation factor equal 5/4.

At 9:45h on the Earth clock, the transmitter sends a FTL signal to the train engine. Let's say it arrives to the engine at 10h on the Earth clock. Because of the time dilation, it is 10*4/5=8h on the train clock. At 9h on the train clock, i.e., one hour later, a car that passes the Earth blows off the transmitter. Because of the time dilation, it is 9*4/5=7h on the Earth clock. The transmitter gets blown off before a transmission is sent (before 9:45h on the Earth clock). But the engine already has received a transmission. It received a transmission that has never been sent. This violates causality.

[Moontanman]

5 minutes ago, Genady said:

In his scenario, yes, the FTL transmission goes from STL ship to Earth. But this is not necessary. The paradox can be demonstrated also without such transmission.

Instead, assume that there is a "train" of STL ships with synchronized clocks between all the "cars" (ships.) The "conductor" of the train made an arrangement that whatever ship passes the Earth at 9h, blows off the FTL transmitter on Earth.

To be specific, let's say that the train moves with 3/5 speed of light. This speed makes a relativistic time dilation factor equal 5/4.

At 9:45h on the Earth clock, the transmitter sends a FTL signal to the train engine. Let's say it arrives to the engine at 10h on the Earth clock. Because of the time dilation, it is 10*4/5=8h on the train clock. At 9h on the train clock, i.e., one hour later, a car that passes the Earth blows off the transmitter. Because of the time dilation, it is 9*4/5=7h on the Earth clock. The transmitter gets blown off before a transmission is sent (before 9:45h on the Earth clock). But the engine already has received a transmission. It received a transmission that has never been sent. This violates causality.

That situation seems more than a bit contrived, how about a FTL transmission isn't possible from a small moving object? Maybe only a planet sized object can be used to house or mount an FTL transmitter? No less contrived at least? 

Edited April 15, 2023 by Moontanman

[Genady]

2 minutes ago, Moontanman said:

That situation seems more than a bit contrived, how about a FTL transmission isn't possible from a small moving object? Maybe only a planet sized object can be used to house or mount an FTL transmitter? No less contrived at least? 

There is no FTL transmission from a small moving object in my scenario. Only from the Earth.

[swansont]

1 hour ago, Moontanman said:

So instantaneous is ok as long as it doesn't come from a moving ship? That is what I thought.  

Instantaneous will violate causality. I’m not sure how that’s OK.

 

[MJ kihara]

Same old problems...we may end up in cycles for another century...the foundation of our understanding about the nature of spacetime fabric....(not the rubber thing analogy or floor mat) is the one that needs to change... issues concerning, about origin of quantum and implications of lorentz factor and of course consciousness ..etc etc and finally our technological know how.

[Moontanman]

4 hours ago, Genady said:

There is no FTL transmission from a small moving object in my scenario. Only from the Earth.

So the train of ships is not moving? 

2 hours ago, swansont said:

Instantaneous will violate causality. I’m not sure how that’s OK.

 

The diagram says differently. 

[Genady]

17 minutes ago, Moontanman said:

So the train of ships is not moving? 

They are moving. They don't send any transmission. They only receive the transmission from Earth.

[MJ kihara]

Causality and information.. just a question...if u read a book then throw it to the blackhole  will you ever be able to retrieve the information in book?

[swansont]

1 hour ago, Moontanman said:

So the train of ships is not moving? 

What train of ships?

The video discusses a supernova and when Vega learns of it. There’s one ship.

1 hour ago, Moontanman said:

The diagram says differently. 

The diagram did not use an instantaneous communication.

You can see the signal took time. Instantaneous would be a horizontal line

 

A FTL ship would be below the null line, rather than above, but it can still arrive later than Vega receiving the warning. An even larger range if the warning is instantaneous.

[MigL]

Are we watchig the same video Moon ?

At 17 min he says 'the problem of causality violation is not with relativity but with FtL itself".
Your misunderstanding may stem from the fact that you are missing an important bit of information which he last explains at 14 min. He says that the "world line defines the time axis as perceived by those following it", further he states "the time axis for the crew of that FtL ship actually lives along that timeline".
The rest of the universe does not.
So while an FtL transmission from an FtL moving ship may not violate causality to those aboard that ship only, the fact remains that they are already violating causality by moving FtL.

I suggest you re-watch without your 'wishful thinking' glasses on.

Edited April 15, 2023 by MigL

[Moontanman]

4 hours ago, Genady said:

They are moving. They don't send any transmission. They only receive the transmission from Earth.

I don't get it, the space time diagram specifically says there is no causality violation under those circumstances. 

2 hours ago, MigL said:

Are we watchig the same video Moon ?

At 17 min he says 'the problem of causality violation is not with relativity but with FtL itself".
Your misunderstanding may stem from the fact that you are missing an important bit of information which he last explains at 14 min. He says that the "world line defines the time axis as perceived by those following it", further he states "the time axis for the crew of that FtL ship actually lives along that timeline".
The rest of the universe does not.
So while an FtL transmission from an FtL moving ship may not violate causality to those aboard that ship only, the fact remains that they are already violating causality by moving FtL.

I suggest you re-watch without your 'wishful thinking' glasses on.

No, he specifically says the transmission doesn't violate causality unless the ship signals back to the earth to shut off it's transmitter.   

2 hours ago, swansont said:

What train of ships?

The video discusses a supernova and when Vega learns of it. There’s one ship.

The diagram did not use an instantaneous communication.

You can see the signal took time. Instantaneous would be a horizontal line

 

A FTL ship would be below the null line, rather than above, but it can still arrive later than Vega receiving the warning. An even larger range if the warning is instantaneous.

You are not looking at the diagram at the beginning. He specifically says the instantaneous transmission by itself would not violate causality.  

2 hours ago, swansont said:

What train of ships?

The video discusses a supernova and when Vega learns of it. There’s one ship.

The diagram did not use an instantaneous communication.

You can see the signal took time. Instantaneous would be a horizontal line

 

A FTL ship would be below the null line, rather than above, but it can still arrive later than Vega receiving the warning. An even larger range if the warning is instantaneous.

The train of ships that Genedy talked about. 

Edited April 15, 2023 by Moontanman

[swansont]

31 minutes ago, Moontanman said:

You are not looking at the diagram at the beginning. He specifically says the instantaneous transmission by itself would not violate causality.  

You keep changing the topic. This was not the point under discussion. The issue was whether a FTL craft could see a causality violation and the answer is yes. It does not require a STL craft.

I suspect he used the STL craft so that there was only one violation of physical law. If there were two, then the source of the violation would be ambiguous.

 

31 minutes ago, Moontanman said:

The train of ships that Genedy talked about. 

We were discussing the video you asked me to watch. Not another example.

[Genady]

42 minutes ago, Moontanman said:

I don't get it, the space time diagram specifically says there is no causality violation under those circumstances. 

Let's look at this diagram from the video, before STL ship receives or sends any messages - just what they "think" happens, i.e., the order of events in their reference frame:

Vega receives the signal, step 1 above, before Earth sends it, step 3 above. The effect occurs before the cause. Isn't it a causality violation?

[Moontanman]

2 hours ago, swansont said:

You keep changing the topic. This was not the point under discussion. The issue was whether a FTL craft could see a causality violation and the answer is yes. It does not require a STL craft.

I suspect he used the STL craft so that there was only one violation of physical law. If there were two, then the source of the violation would be ambiguous.

 

We were discussing the video you asked me to watch. Not another example.

I was not answering you when I mentioned the space ship train. I am trying to reply to everyone, not just you. 

1 hour ago, Genady said:

Let's look at this diagram from the video, before STL ship receives or sends any messages - just what they "think" happens, i.e., the order of events in their reference frame:

Vega receives the signal, step 1 above, before Earth sends it, step 3 above. The effect occurs before the cause. Isn't it a causality violation?

It's must be my wishful thinking that is clouding my tiny brain... I'll continue to take your word for it, I must be missing something. I knew I shouldn't have posted this video, only served to make me look stupid for asking the question. 

[swansont]

1 hour ago, Moontanman said:

I was not answering you when I mentioned the space ship train. I am trying to reply to everyone, not just you. 

I’m only responding to what you say when you quote me. That’s presumably a reply to me.

[zapatos]

1 hour ago, swansont said:

I’m only responding to what you say when you quote me. That’s presumably a reply to me.

I think he was quoting Genady when he asked about the train of ships.

[MJ kihara]

7 hours ago, Genady said:

Let's look at this diagram from the video, before STL ship receives or sends any messages - just what they "think" happens, i.e., the order of events in their reference frame:

Vega receives the signal, step 1 above, before Earth sends it, step 3 above. The effect occurs before the cause. Isn't it a causality violation?

According to that diagram effect occur before cause for STL Ship ...look at it's space axis...I think if there is an error is from the way he obtained STL space axis it doesn't seem to be on the same space axis with Earth and Vegas.

5 hours ago, Moontanman said:

I knew I shouldn't have posted this video, only served to make me look stupid for asking the question. 

I think in science progress is brought by discussions, arguments,reexaming what you know... accepting challenges... nothing like looking stupid.

[Moontanman]

5 hours ago, swansont said:

I’m only responding to what you say when you quote me. That’s presumably a reply to me.

I'm sorry I thought I was quoting Genedy, my bad, and my bad for not understanding what the video is saying. It's been bothering me since I first watched it, I know what everyone says about FTL being time travel but for some reason I see something different in the diagram as explained by the guy in the video. I know what I am supposed to see but it looks quite different to me for some reason that I can't quite put my finger on. 

1 hour ago, MJ kihara said:

According to that diagram effect occur before cause for STL Ship ...look at it's space axis...I think if there is an error is from the way he obtained STL space axis it doesn't seem to be on the same space axis with Earth and Vegas.

I think in science progress is brought by discussions, arguments,reexaming what you know... accepting challenges... nothing like looking stupid.

The problem is my misperception, for some reason the diagram is tripping me up. 

[Genady]

4 hours ago, MJ kihara said:

According to that diagram effect occur before cause for STL Ship ...look at it's space axis...I think if there is an error is from the way he obtained STL space axis it doesn't seem to be on the same space axis with Earth and Vegas.

There is no error. The STL space axis is not the same as the space axis of Earth and Vega because the ship moves relative to Earth and Vega.

[MJ kihara]

53 minutes ago, Genady said:

There is no error. The STL space axis is not the same as the space axis of Earth and Vega because the ship moves relative to Earth and Vega.

In that case once the STL perceives all the events..four events.. that's Step1 Vega receives a signal,step2 supernova,step3 Earth sends a signal and step4 Vega sees supernova...the STL crew will realise there is an anormaly in the sequence of events....given that they know they are moving at STL...I think they will be able to extrapolate the right sequence of events therefore causality will not have been violated.

[Genady]

11 minutes ago, MJ kihara said:

In that case once the STL perceives all the events..four events.. that's Step1 Vega receives a signal,step2 supernova,step3 Earth sends a signal and step4 Vega sees supernova...the STL crew will realise there is an anormaly in the sequence of events....given that they know they are moving at STL...I think they will be able to extrapolate the right sequence of events therefore causality will not have been violated.

They don't have a way to know that they are moving. All they know is that Earth and Vega move relative to them.

[MJ kihara]

34 minutes ago, Genady said:

They don't have a way to know that they are moving. All they know is that Earth and Vega move relative to them.

I think They will know given the invariance of light speed and age of the universe as they will use them as a point of reference....unless they are in parallel universe where constant c and age of their universe is different.

[Genady]

1 minute ago, MJ kihara said:

I think They will know given the invariance of light speed and age of the universe as they will use them as a point of reference.

No, this will not help them to know that they are moving. Remember that Earth and Vega also move, relative to some other stars. Everything moves relative to something. There is no difference between frames that are in free move.