The speed of light and causality

[geordief]

 We have an intelligent community living in an environment  where the speed of light is slowed by the medium they live and communicate in  .

 

Then they discover a method  to create channels through the medium so that they can now  pass messages at the speed of light.

Will it seem to them that " causality has been broken"?

Is this scenario an accurate analogy to us discovering a faster than light process of signaling?

[swansont]

Causality is limited by c, which is the speed of light in vacuum, not the speed of light in a medium. There isn’t a scenario where an answer arrives before you send a message for signals slower than c.

[Lorentz Jr]

12 minutes ago, geordief said:

Is this scenario an accurate analogy to us discovering a faster than light process of signaling?

That can't happen in relativity, so your question would be better off in the Speculations area. Otherwise, as swansont explained, the answer is no, there's no analogy between exceeding c and reaching c.

Edited February 9, 2023 by Lorentz Jr

[Genady]

Causality is not defined by the speed of light. It is defined/limited by a speed equal to some number, c, whose numerical value depends on the units of distance and time.

Light propagates in vacuum with the same speed c, just as any massless particles, and gravitational waves. The causality and the speed of light in vacuum are correlated, but they do not cause each other.

[geordief]

I was hoping to get an answer to my particular  scenario.

Do the intelligent beings living under those circumstances (nothing in their environment  moves faster than w (the speed of light on their environment -the same in all directions) have a (possibly  flawed) belief that causality in connected to w?

Will   they be dumbfounded when the channels are created where signals travel at c and will those who still operate at the old speed of w be under the impression that  "causality has been broken" until they get up to speed with the new reality?

 

Edit I have just  seen a (the ) flaw in my scenario: w will not be the same in all directions. 

Edited February 9, 2023 by geordief

[Genady]

5 minutes ago, geordief said:

Do the intelligent beings living under those circumstances (nothing in their environment  moves faster than w (the speed of light on their environment -the same in all directions) have a )possibly  flawed) belief that causality in connected to w?

I think they will not. It has already happened. Nothing in our environment moves faster than c/w/z, but until SR we believed that causality speed is unlimited.

Edited February 9, 2023 by Genady

[Lorentz Jr]

9 minutes ago, Genady said:

Nothing in our environment moves faster than c/w/z, but until SR we believed that causality speed is unlimited.

And even if they did know about relativity without having access to a vacuum, they might be able to infer the real value of c from the electromagnetic constants and other phenomena, such as how muon decay rates depend on their speed. Maybe that's a stretch, I don't know. Their access to good experimental data might also be limited.

Edited February 9, 2023 by Lorentz Jr

[geordief]

6 minutes ago, Lorentz Jr said:

And even if they did know about relativity without having access to a vacuum, I think they would be able to infer the real value of c from the electromagnetic constants and other phenomena, such as how muon decay rates depend on their speed. Maybe that's a stretch, I don't know. Their access to good experimental data might also be limited. But it seems unlikely to me that they could mistake their slow speeds for c. They would know they don't live in a vacuum.

They wouldn't have invariance of w ,would they?

[Genady]

7 minutes ago, geordief said:

They wouldn't have invariance of w ,would they?

They wouldn't.

 

w, not c.

edit: x-posted with @Lorentz Jr

Edited February 9, 2023 by Genady

[Lorentz Jr]

[deleted]

Edited February 9, 2023 by Lorentz Jr

[geordief]

3 minutes ago, Lorentz Jr said:

You mean c? I don't see why not. Did Michelson and Morley need a vacuum?

No ,I meant that their top speed ,w would not have the same properties as a top speed in a vacuum (c) .

I am not  not sure if they would still associate w with the speed of causality or not 

Edited February 9, 2023 by geordief

[Lorentz Jr]

Just now, geordief said:

No ,I meant that their top speed ,w

Sorry. My fingers were going faster than my brain. 🙄

[geordief]

1 minute ago, Lorentz Jr said:

Sorry. My fingers were going faster than my brain. 🙄

Slow posting speeds suit my slow brain(even then I struggle)

[Lorentz Jr]

3 minutes ago, geordief said:

I am not  not sure if they would still associate w with the speed of causality or not

No, Grenady and I both doubt they would. My point was that all their data would still extrapolate out to c, even if they can't reach it experimentally.

[geordief]

13 minutes ago, Lorentz Jr said:

No, Grenady and I both doubt they would. My point was that all their data would still extrapolate out to c, even if they can't reach it experimentally.

If that is the case then we do not seem to  have any corresponding  greater than c speed out to which we could extrapolate even in theory(I think)

Any discussion I have heard centres on how we might detect a tachyon if it existed.(no ref,sorry)

[Boltzmannbrain]

On 2/9/2023 at 7:40 AM, geordief said:

 We have an intelligent community living in an environment  where the speed of light is slowed by the medium they live and communicate in  .

 

Then they discover a method  to create channels through the medium so that they can now  pass messages at the speed of light.

Will it seem to them that " causality has been broken"?

Is this scenario an accurate analogy to us discovering a faster than light process of signaling?

Actually, the speed of light is slowed by the environment that we are living in.  The speed of light slows in the presence of electrons, which are everywhere.  The real speed of light is in very spall spaces if it exists at all.  

 

Edited February 19, 2023 by Boltzmannbrain

[geordief]

19 minutes ago, Boltzmannbrain said:

 The real speed of light is in very spall spaces if it exists at all.  

 

As I heard it light moves  either at c or at zero with no other speed  in between.Everything  between interactions  is the vacuum where the speed of light is c and I confess to knowing very little of the processes that  actually go on during interactions with the medium,or how long 1 such interaction might take (which slows down the overall speed of light in any particular medium)

[Boltzmannbrain]

4 minutes ago, geordief said:

As I heard it light moves  either at c or at zero with no other speed  in between.Everything  between interactions  is the vacuum where the speed of light is c and I confess to knowing very little of the processes that  actually go on during interactions with the medium,or how long 1 such interaction might take (which slows down the overall speed of light in any particular medium)

That is what a lot of people think.  It actually slows down.  This video explains it perfectly,  

 

Edited February 19, 2023 by Boltzmannbrain

[geordief]

6 minutes ago, Boltzmannbrain said:

That is what a lot of people think.  It actually slows down.  This video explains it perfectly,  

 

So interactions with particles don't "hold up" the passage of the light?

It is the presence of electrons which  create  their own wave  which interferes with the light wave,producing  a resultant wave to move at a speed lower than c?

[Boltzmannbrain]

1 minute ago, geordief said:

So interactions with particles don't "hold up" the passage of the light?

I don't know a lot about all this, but I know that electrons also absorb light, which I believe is "holding it up".

Quote

It is the presence of electrons which  create  their own wave  which interferes with the light wave,producing  a resultant wave to move at a speed lower than c?

Yeah, that's how I understand it.

[swansont]

35 minutes ago, geordief said:

As I heard it light moves  either at c or at zero with no other speed  in between.Everything  between interactions  is the vacuum where the speed of light is c and I confess to knowing very little of the processes that  actually go on during interactions with the medium,or how long 1 such interaction might take (which slows down the overall speed of light in any particular medium)

You have to pay attention to detail in what is said. 

Light slows down in a medium. Photons do not.  — talking about light and talking about photons are not exactly the same thing.

[MigL]

We are aware of cases where  the speed of light is exceeded in some particular medium.
Not the speed of light in  vacuum, mind you, but the speed of light in that particular medium.
This results in a lovely blue emission called Cerenkov Radiation, but, no causality violations of any kind.

I don't imagine your hypotethical intelligent community would note any causality violations either.

[Boltzmannbrain]

26 minutes ago, swansont said:

You have to pay attention to detail in what is said. 

Light slows down in a medium. Photons do not.  — talking about light and talking about photons are not exactly the same thing.

What do you mean?  The photons are the light.

[geordief]

35 minutes ago, swansont said:

You have to pay attention to detail in what is said. 

 

Ah yes ,but the distinction btw the quantum and the classical model  is far from second nature to me.

 

But thanks for the  reminder.

Edited February 19, 2023 by geordief

[Genady]

1 hour ago, Boltzmannbrain said:

It actually slows down.  This video explains it perfectly

I watched the video. I did not see an explanation why it actually slows down. It just says it does. Why the sum of these two waves, let's call them primary and secondary, moves slower than the primary one?