Is FTL actually possible?

[MJ kihara]

8 minutes ago, Genady said:

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.

I would like to know if STL ship is free falling or have some mechanism of propulsion?

Because if it has some propulsion mechanism they will send light signal to another comoving reference point and calculate the time taken for light signal to come back given that c is known the distance will be determined...using this distance and the time they cover part of it when their ship accelerate...they will know their ship is moving at STL.

[Genady]

14 minutes ago, MJ kihara said:

I would like to know if STL ship is free falling or have some mechanism of propulsion?

It is free falling.

[MJ kihara]

11 minutes ago, Genady said:

It is free falling.

If so even Vega, supernova,Earth sending signal and vega receiving signal are free falling...if both are in a uniform gravitational fields...then STL ship as it is free falling in tandem with them, will be receiving signal from them depending on how far they are and in this case STL crew will use distance to extrapolate sequence of events therefore eliminate causality violation.

[MJ kihara]

1 hour ago, MJ kihara said:

...will be receiving signal from them depending on how far they are and in this case STL crew will use distance to extrapolate sequence of events therefore eliminate causality violation.

In this case the signal will be moving at speed of light.

However,if the signal is instantaneous they will know as the events are taking place and they will be able to extrapolate what will happen to Earth and Vegas to a future date but their knowledge will not cause causality violation since they are limited by their STL ship...the crew in this ship becomes dreamers of the future...when themselves try to send signal at FTL or instantaneous to warn Earth and Vegas...it will be a contradiction and it violates causality.

 

[Janus]

On 4/15/2023 at 5:35 AM, 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? 

How does that address the issue?  Sure, it would be impracticable to do a similar scenario just using planet-sized objects, but it is not strictly impossible. 

As far as the basic scenario being "contrived" goes,   what does that matter?  This isn't about every or even most scenarios causing causality issues,  it is about being able to produce them at all. One way to violate causality is one too many.

[swansont]

12 hours ago, zapatos said:

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

Yes, my mistake. Apologies to @Moontanman

[Genady]

2 hours ago, MJ kihara said:

If so even Vega, supernova,Earth sending signal and vega receiving signal are free falling...if both are in a uniform gravitational fields...then STL ship as it is free falling in tandem with them...

This is incorrect. They move relative to each other as they all free fall in a uniform gravitational field. So, the causality violation happens as is shown on the diagram, and there is no way to "extrapolate" it away.

[MJ kihara]

20 minutes ago, Genady said:

They move relative to each other as they all free fall in a uniform gravitational field.

How will they move relative to each other if they don't have any means of propulsion as you have agreed.... objects freefall at the same rate when in a uniform gravitational field.

[Genady]

1 minute ago, MJ kihara said:

How will they move relative to each other if they don't have any means of propulsion as you have agreed.... objects freefall at the same rate when in a uniform gravitational field.

Let one object fall straight down and at the same time throw another object horizontally. While free falling at the same rate, they will be moving relative to each other.

[MJ kihara]

1 hour ago, Genady said:

Let one object fall straight down and at the same time throw another object horizontally. While free falling at the same rate, they will be moving relative to each other.

That's right.

19 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:

 

Then from the diagram STL space axis,it's time axis should be perpendicular to it..from there plot null line...in these case his STL ship will be moving FTL cause the angle between STL space axis and STL ship is less than 45 degrees as it appears...if so, it then means he is giving contradictory explanations.Perharps taking me back to my earlier statement an error occurred as he ( in the video) was making STL space axis.

[Genady]

15 minutes ago, MJ kihara said:

ship will be moving FTL cause the angle between STL space axis and STL ship is less than 45 degrees

The speed, in the units of c, is equal to tan of the angle between the ship's worldline and the Earth time axis. It is less than 45⁰, so its speed is less than c. There is no error.

[MJ kihara]

19 minutes ago, Genady said:

The speed, in the units of c, is equal to tan of the angle between the ship's worldline and the Earth time axis. It is less than 45⁰, so its speed is less than c. There is no error.

Just some clarification...ship's world line and ship's space axis are being referenced to Earth time axis?

[Genady]

2 minutes ago, MJ kihara said:

Just some clarification...ship's world line and ship's space axis are being referenced to Earth time axis?

If you mean that the diagram is drawn in the Earth's, and the Vega's, reference frame, then yes.

[Moontanman]

I have a question, where does the space diagram come from and how do we know it is an accurate representation of reality? The diagram seems to be the fly in the ointment, I know it is assumed to be accurate by the youtube poster and by everyone here but why? 

[Genady]

2 minutes ago, Moontanman said:

I have a question, where does the space diagram come from and how do we know it is an accurate representation of reality? The diagram seems to be the fly in the ointment, I know it is assumed to be accurate by the youtube poster and by everyone here but why? 

Straight from special relativity.

[Moontanman]

7 minutes ago, Genady said:

Straight from special relativity.

I do understand that and I understand Special Relativity came from Einstein but why or how does that result in this diagram?   

[Genady]

Just now, Moontanman said:

I do understand that and I understand Special Relativity came from Einstein but why or how does that result in this diagram?   

They are diagrammatic representations of Lorentz transformations, which connect spacetime coordinates between inertial frames moving relative to each other.

[Moontanman]

1 hour ago, Genady said:

They are diagrammatic representations of Lorentz transformations, which connect spacetime coordinates between inertial frames moving relative to each other.

Sadly I guess this is just one more thing I'll have to accept on faith or at least my trust in others who know more than me... ok, no other choice I guess. I but I do have to ask is this final or could some other breakthrough in science like solving the connection between the quantum mechanics, relativity, and gravity bring about an understanding that makes this diagram obsolete? Is there any work in that direction at all?     

[swansont]

It’s not even Lorentz transforms being shown. Just x vs ct.

Light travels at c, so it shows up as a 45 degree line (the null line). If you go slower it takes longer to go some distance x, so that will appear above (steeper). FTL would go below. Both cases are depicted - one for the FTL signal, one for the STL ship.

If you didn’t move it would show up as a vertical line - motion through time but not space.

The Lorentz transforms would show up if you rotated this to be in the ship’s frame.

[Genady]

31 minutes ago, Moontanman said:

Sadly I guess this is just one more thing I'll have to accept on faith or at least my trust in others who know more than me... ok, no other choice I guess. I but I do have to ask is this final or could some other breakthrough in science like solving the connection between the quantum mechanics, relativity, and gravity bring about an understanding that makes this diagram obsolete? Is there any work in that direction at all?     

It is fundamental for theories and tested in experiments and observations on all levels of physics: quantum field, standard model, high energy, astrophysics, gravitation, cosmology, etc. AFAIK, there is no hint that it will or might go away.

 

15 minutes ago, swansont said:

The Lorentz transforms would show up if you rotated this to be in the ship’s frame.

When they compare the order of events between the Earth frame and the ship's frame on the same diagram, they apply Lorentz transforms implicitly.

[Moontanman]

1 hour ago, swansont said:

It’s not even Lorentz transforms being shown. Just x vs ct.

Light travels at c, so it shows up as a 45 degree line (the null line). If you go slower it takes longer to go some distance x, so that will appear above (steeper). FTL would go below. Both cases are depicted - one for the FTL signal, one for the STL ship.

If you didn’t move it would show up as a vertical line - motion through time but not space.

The Lorentz transforms would show up if you rotated this to be in the ship’s frame.

 

43 minutes ago, Genady said:

It is fundamental for theories and tested in experiments and observations on all levels of physics: quantum field, standard model, high energy, astrophysics, gravitation, cosmology, etc. AFAIK, there is no hint that it will or might go away.

 

When they compare the order of events between the Earth frame and the ship's frame on the same diagram, they apply Lorentz transforms implicitly.

How does instantaneous transmission of a signal show up?  

[Genady]

7 minutes ago, Moontanman said:

 

How does instantaneous transmission of a signal show up?  

A transmission that is instantaneous in the Earth frame goes parallel to the Earth's space axis, the horizontal axis on the diagram.

A transmission that is instantaneous in the ship frame goes parallel to the ship's space axis, the sloped dashed line on the diagram.

Edited April 16, 2023 by Genady
typo

[Moontanman]

Just now, Genady said:

A transmission that is instantaneous in the Earth frame goes parallel to the Earth's space axis, the horizontal axis on the diagram.

A transmission that is instantaneous in the ship frame goes parallel to the ship's space axis, the slopped dashed line on the diagram.

So an instant transmission directly to vega from sol would not violate causality as is explained in the video but a instant transmission from a spacecraft would? 

[Genady]

1 minute ago, Moontanman said:

So an instant transmission directly to vega from sol would not violate causality as is explained in the video but a instant transmission from a spacecraft would? 

Any instant transmission in one frame violates causality in other frame. There is no physical difference between frames.

[swansont]

8 minutes ago, Moontanman said:

So an instant transmission directly to vega from sol would not violate causality as is explained in the video but a instant transmission from a spacecraft would? 

It would violate it just as explained in the video. Instantaneous is just the most extreme case of FTL.