[Iggy]

Mystery111, on 27 October 2011 - 01:15 AM, said:

I didn't qoute that, so you are misrepresenting the facts.

Eh? You quoted it here:

Mystery111, on 26 October 2011 - 10:52 PM, said:

Iggy, on 26 October 2011 - 10:26 PM, said:

The speed of light is special because it's invariant. That is what makes c special, and the existence of speeds faster than c would make c no less special in that regard. If something travels FTL in one frame then it travels back in time in another frame -- not because light is the fastest speed of communication, but because it is invariant (the same in every frame).

Highlighted part: agreed.

Non-highlighted part: A timelike tachyon does, not a spacelike tachyon which was the point I was raising earlier. Some models go back as far as the 60's which try to circumvent the problem of a faster than light particle which would oscillate throughout time and the causality problems which closely asist it.

The non-highlighted part is what I repeated.

Mystery111, on 27 October 2011 - 01:15 AM, said:

My post qouted you talking about knowing very little on tachyons, then asking me what a spacelike condition has to do for a tachyon. I explained to you that was one solution I referenced before and if you wanted those references you would need to go back. Secondly I explored a further option.

So qouting me like you did is disingenuous.

Oh, my!

I still don't get why you disagreed with post #35 nor what you meant by "timelike tachyons". The material you referenced reinforced the thing I said and the footnote it gave specifically equates "spacelike 4-momentum" with "faster than light" (i.e. tachyons). I don't believe that the argument you cited anywhere claims that tachyons can be taken as timelike or understood in any way to travel slower than light.

It seems like you disagreed with my post for reasons that don't disagree with my post.

Maybe it's a little off topic though and we should just leave it... ?

This post has been edited by Iggy: 27 October 2011 - 01:41 AM

[Mystery111]

Iggy, on 27 October 2011 - 01:41 AM, said:

Eh? You quoted it here:



The non-highlighted part is what I repeated.


Oh, my!

I still don't get why you disagreed with post #35 nor what you meant by "timelike tachyons". The material you referenced reinforced the thing I said and the footnote it gave specifically equates "spacelike 4-momentum" with "faster than light" (i.e. tachyons). I don't believe that the argument you cited anywhere claims that tachyons can be taken as timelike or understood in any way to travel slower than light.

It seems like you disagreed with my post for reasons that don't disagree with my post.

Maybe it's a little off topic though and we should just leave it... ?

Because I said the first part was agreed with, and not confirmed the second part, that was my fault I guess.

I was not disagreeing, I was adding to the different interpretations of tachyons. Nowhere in that reference you made of me:

''Non-highlighted part: A timelike tachyon does, not a spacelike tachyon which was the point I was raising earlier. Some models go back as far as the 60's which try to circumvent the problem of a faster than light particle which would oscillate throughout time and the causality problems which closely asist it.''

Contains anywhere that I disagreed with your post. You brought up causality, which is what is implied by that model you speak of. That is why my reference to the non-highlighted part was in nature of the problem of causality offerring other solutions, which I gave.

[Moontanman]

swansont, on 26 October 2011 - 09:37 PM, said:

I wasn't sure what your point was; you seemed to be saying you can get a signal before you send it if you can communicate at the speed of light. That's not true.


I don't see why FTL would somehow negate the causality violation. If the rest of relativity still held, the example given shows how you can violate causality.

What i had in mind was that if you did have a method of communicating faster than light then the causality thing would only apply to observers who were limited to speed of light?

Here is the thought experiment i was thinking of, lets say that I somehow construct a "radio" that communicates instantaneously. I turn it on and hear a voice and manage somehow to talk to it, i find out it is originating from the Andromeda Galaxy, we talk with no time lag, I could be so far off the mark here but indulge me a second or two more. From the stand point of relativity would we both be speaking to each other in each others future? I think Andromeda is a million light years or so away, if I had immediate access to Andromeda wouldn't mean i was talking to the guy in the past and he was speaking to me in his past? One million years in our pasts because we are one million light years from each other? Ok, now I'm really confused damn it....

[granpa]

if you and the person in andromeda are stationary with respect to each other then you are both in each others present.

[Moontanman]

granpa, on 28 October 2011 - 12:32 AM, said:

if you and the person in andromeda are stationary with respect to each other then you are both in each others present.

Can you elaborate? Considering the idea that there is no universal reference frame or are you saying there is a universal reference frame?

[swansont]

Moontanman, on 28 October 2011 - 01:11 AM, said:

Can you elaborate? Considering the idea that there is no universal reference frame or are you saying there is a universal reference frame?

No. If you are at rest with respect to each other, you are in the same reference frame. You can synchronize clocks and can agree on what time it is.

[Moontanman]

swansont, on 28 October 2011 - 09:45 AM, said:

No. If you are at rest with respect to each other, you are in the same reference frame. You can synchronize clocks and can agree on what time it is.

So if we are both traveling at the same speed we can communicate faster than light?

[swansont]

Moontanman, on 28 October 2011 - 02:17 PM, said:

So if we are both traveling at the same speed we can communicate faster than light?

You offered that as a premise in your scenario. If you have a method of communicating faster than light, then you have a method of communicating faster than light.

[JohnB]

At irregular intervals I try to understand Lorentz Transformations without having my brains drain from my ears. Perhaps like others I can understand the logic as given by swansonts link, but I can't conceptualise it all.

I see how causality is violated due to the pretty slanted lines in the diagram, but I don't see how it works. I think of it this way. Say I have 4 ships each at a different star some 10 LY from Earth and each star is 10 LY from its neighbour. A ship takes 1 week to travel 10 LY. I send out a ship with a recall message. So the recall ship arrives at Star A after 1 week and passes on the message. The recall ship heads to the next Star while the Star A ship heads home. At the end of the second week the Star A ship arrives home and the recall ship arrives at Star B. At the end of the third week, the ship from Star B arrives home and the recall ship is at Star C. At the end of the fourth week the ship from Star C arrives home and the recall ship is at Star D. At the end of the fifth week both the Star D ship and the recall ship arrive home.

How is causality violated? Or is there no transformation because the ships awaiting the recall are sort of "at rest" and are therefore in the same frame as I am?

Now for the biggy. It strikes me that one definition of Minkowski Spacetime is that it is a construct where FTL will result in causality violations. What if when travelling FTL you are no longer in Minkowski Spacetime? Why would the same rules apply. Because I'm at the "really dumb" end of the relativity spectrum here I'm thinking in similar terms to geometry. One could define Euclidian geometry as a world where parallel lines remain the same distance apart. As soon as this basis changes, then you are no longer in Euclidian space and the rules don't apply. Probably very wrongly I'm thinking of Minkowski as defining the geometry of spacetime in a similar fashion to Euclid and surfaces.

Another question that I have to ask is "Does relativity apply to dark matter and energy?" I just can't see why it would. DM virtually ignores the world of baryonic matter and the EM spectrum. Why would rules formulated to describe and dependent upon the baryonic world and the EM spectrum have any relevence to non baryonic matter and non EM forms of energy?

[swansont]

I have a cold, so dissecting the problem isn't in the cards ATM, but suffice to say that FTL means you can violate causality, not that all scenarios will violate causality.

[Widdekind]

swansont, on 17 October 2011 - 10:43 PM, said:

http://www.thecultur...ves/000089.html

Is there an easy way of visualizing the effect? "Everybody knows", that relativistic boosts "collapse" the moving observer's x,t "grid", a little like some form of folding fence. So, "everybody knows", that relativistic observers' "lines of simultaneity" (t=const) "slash diagonally across" some fiducial stationary observer's grid. And, exaggerating for simplicity, FTL signals that were infinitely FTL would "zip" along lines of simultaneity, covering immense distances, in negligible time. So, someone moving relativistically "to the right", firing an FTL beam "to the left", would look like they had "communicated backwards in time" (to the stationary observer).

Quantum non-local instaneity, exploiting entangled wave-functions, which had previously been propagated conventionally, could possibly avoid violating Causality, if the original luminal signal was "pregnant with the possibility" subsequently manifested, cp. "consistent histories". In the following figure, events Q&R could hypothetically manifest some seemingly supra-luminal "synchronicity", had they both been synchronized, Causally, from the vertex at the intersection of both events backwards light-cones. Perhaps exploiting quantum entanglement would be somewhat similar to such a "synchronization"?