Constancy of SOL from all objects

[Strange]

No no.

I simply mean:

You can keep c as an invariant, you can keep "No matter how fast that object was moving". You can keep c as the velocity of causality. You can keep all of Relativity and keep being consistent with observation.

Don't you agree?

 

 

Not unless you can produce a model that matches observations.

 

And matches all the evidence.

 

How does this explain the CMB, for example?

[michel123456]

Tachyons is what you are looking for - but they would violate causality as we know it.

 

It is another thing of "violating causality" and "being unrelated through direct causality".

[ajb]

It is another thing of "violating causality" and "being unrelated through direct causality".

If tachyons are realised in nature, then it is possible to find a reference frames for which the tachyons move backwards in time. Thus it would be possible to send messages back in time - this violates causality. Unless maybe you can find some reason why one cannot actually uses tachyons to send information.

[michel123456]

Why don't you simply ask the question?

 

You have an object A moving away from you at velocity V. This object A emits light. What is the velocity of light (SOL)for the followings:

 

V=0, SOL=c

V=1m/s, SOL=c

V=10m/s, SOL=c

V=100000m/s, SOL=c

V=299999km/s, SOL=c

 

Is the above correct?

 

And then why would we think that suddenly the value of V matters when V gets higher than that?

 

In a world without expansion.

 

Why would suddenly c drop to zero for objects traveling at c and thus become unobservable.

Why would the photons go backwards when the source is going faster than c?

 

Especially after having stated that velocity doesn't matter because c is an invariant.

[ajb]

Why would suddenly c drop to zero for objects traveling at c and thus become unobservable.

I am not sure what you mean by this. The problem is that there are no inertial frames for which a photon can be considered at rest. You need to be careful here.

 

Why would the photons go backwards when the source is going faster than c?

What do you mean by backwards? Backwards in time?

 

Especially after having stated that velocity doesn't matter because c is an invariant.

When switching between inertial frames.

[Strange]

Why don't you simply ask the question?

 

Why would suddenly c drop to zero for objects traveling at c and thus become unobservable.

Why would the photons go backwards when the source is going faster than c?

 

 

That isn't what happens.

 

I'm not really sure where your misunderstanding is. The expansion of space between us and a distant galaxy means that light takes longer to reach us than it would if there were no expansion. At some point that "takes longer" becomes never. It has nothing to do with things travelling faster than c. Photons never go backwards. (1) Nothing can travel faster than c. (2) We can observer galaxies that are receding faster than c.

Edited July 24, 2016 by Strange

[MigL]

Expansion is NOT a speed or velocity, relative or otherwise.

If you just consider it 'increasing separation', there will be much less confusion.

[michel123456]

 

 

That isn't what happens.

 

I'm not really sure where your misunderstanding is. The expansion of space between us and a distant galaxy means that light takes longer to reach us than it would if there were no expansion. At some point that "takes longer" becomes never. It has nothing to do with things travelling faster than c. Photons never go backwards. (1) Nothing can travel faster than c. (2) We can observer galaxies that are receding faster than c.

In a world without expansion of space.

 

Look

I know the understanding of Relativity is that nothing can go faster than C.

That means: in a world without expansion the entire Universe is observable.

Is that correct so far?

[Strange]

In a world without expansion of space.

 

Look

I know the understanding of Relativity is that nothing can go faster than C.

That means: in a world without expansion the entire Universe is observable.

Is that correct so far?

 

 

The entire universe is observable (assuming that it is infinitely old). Hence Olbers' paradox.

https://en.wikipedia.org/wiki/Olbers%27_paradox

[swansont]

 

The only thing that you must drop off is "nothing can go faster than c" and replace it with "c is the max velocity of causality".

 

 

How can something travel faster than causality? It would allow you to violate causality.

[michel123456]

 

 

How can something travel faster than causality? It would allow you to violate causality.

I don't know. Maybe things that are totally unrelated. Objects that are not bind by causality.

[Strange]

I don't know. Maybe things that are totally unrelated. Objects that are not bind by causality.

 

 

In which case there is no way of defining their relative speed.

[swansont]

I don't know. Maybe things that are totally unrelated. Objects that are not bind by causality.

 

 

Objects not bound by causality are ones separated by d > ct. But having "causality" travel faster than c renders this meaningless. You could have something be caused before the action that caused it happens.

[michel123456]

 

 

In which case there is no way of defining their relative speed.

That is part of my question. If c is invariant, there is a way.

 

 

Objects not bound by causality are ones separated by d > ct. But having "causality" travel faster than c renders this meaningless. You could have something be caused before the action that caused it happens.

Could you please re-word the bold part?

Edited July 25, 2016 by michel123456

[Strange]

That is part of my question. If c is invariant, there is a way.

 

Not if they are causally disconnected. How could you compare times, positions, speeds, when there can be no communication of information, even in principle.

[swansont]

 

Could you please re-word the bold part?

 

 

 

If event A causes event B, but the speed of causality exceeds c, you could get the results of B before A happens.

[michel123456]

 

Not if they are causally disconnected. How could you compare times, positions, speeds, when there can be no communication of information, even in principle.

Why?

Are you also one of those who think photons can stop mid-air as in the link at the begin of this thread?

 

 

 

If event A causes event B, but the speed of causality exceeds c, you could get the results of B before A happens.

Right.

But if A and B are unrelated there is no upper limit for unrelated events.

Anyway I don't want to jump into conclusions. My question is about the "no matter the velocity" versus "nothing can travel faster than c".

 

IMHO IF and if an object A travels faster than c relative to object B (where A and B are not bound by any causality), then A will be observable by B and reversely, because the "no matter the velocity" statement still holds.

Edited July 25, 2016 by michel123456

[Strange]

Why?

 

If they cannot communicate any information, then they cannot compare any of their measurements and therefore cannot compare their speeds.

 

Are you also one of those who think photons can stop mid-air as in the link at the begin of this thread?

 

Does anyone think that? Is that just a straw man argument?

[swansont]

 

But if A and B are unrelated there is no upper limit for unrelated events.

 

 

That's not where the problem arises, so that's not the issue. It's irrelevant.

[michel123456]

 

If they cannot communicate any information, then they cannot compare any of their measurements and therefore cannot compare their speeds.

 

 

Does anyone think that? Is that just a straw man argument?

Sorry for that. The author of the link seems to think that. Of course under the space expansion prism.

[Strange]

Sorry for that. The author of the link seems to think that. Of course under the space expansion prism.

 

Or maybe you just don't understand it.

[michel123456]

 

Or maybe you just don't understand it.

I still wonder if you understand my question.

 

If you draw a graph of peculiar velocities and corresponding velocity of light you obtain something like this

 

On the X axis you have peculiar velocities of objects (relative motion)

On the Y axis you have the speed of light.

Since SOL is constant, on the diagram it is represented as a solid line. The line stops abruptly at Vpeculiar = c

Is that correct so far?

And if it is correct, does that make sense that if (IF) relative motion exceeds c (for any reason*) then SOL will remain c. Which means that the Speed of Light emanating from objects moving at over-c velocity will still be observed as c. Even in a world without expansion.

 

*I understand very well that expansion is a way to explain over-c apparent velocity, but that is another story.

[MigL]

You have the wrong idea about causality.

No relationship need be involved.

 

And expansion is still NOT a speed, information transfer or causal connection.

[michel123456]

You have the wrong idea about causality.

No relationship need be involved.

 

And expansion is still NOT a speed, information transfer or causal connection.

I don't understand your comment. Expansion is able to transport clusters of galaxies. Expansion allow photons to "jump the gaps" that appear when space expands. It is not a speed, I agree, but expansion "expands" information transfer and causality.

Anyway

My question is still about invariance of c in a world without expansion.

[Strange]

Since SOL is constant, on the diagram it is represented as a solid line. The line stops abruptly at Vpeculiar = c

Is that correct so far?

 

I suppose so. It seems an unnecessarily complicated way of saying "c is invariant".

 

 

And if it is correct, does that make sense that if (IF) relative motion exceeds c (for any reason*) then SOL will remain c.

Which means that the Speed of Light emanating from objects moving at over-c velocity will still be observed as c. Even in a world without expansion.

 

As you are talking about the impossible, there isn't really a scientific answer to that.

 

 

*I understand very well that expansion is a way to explain over-c apparent velocity, but that is another story.

 

Not really. The fact that we can observe objects with an apparent recessional rate greater than c is a consequence of expansion, not the reason.

I don't understand your comment. Expansion is able to transport clusters of galaxies. Expansion allow photons to "jump the gaps" that appear when space expands. It is not a speed, I agree, but expansion "expands" information transfer and causality.

 

I'm not sure what any of that means.

 

 

My question is still about invariance of c in a world without expansion.

 

And, again, c is invariant. With or without expansion.

 

And before you ask again: without expansion, c is invariant. You know, it is the same for all observers.

Oh, and with expansion, c is invariant. You know, it is the same for all observers.

 

In other words, c is invariant.

 

OK?

 

(Of course, one consequence of c being invariant is the theory of relativity. And hence expansion.)

 

Now, what was the question we don't understand? Oh yes, whether c is invariant without expansion. I think the answer to that is yes.