[paultrr]

Galaxy recession is brought about by the expansion of spacetime itself. Now while true that galaxies have rest mass, their own local motion is never FTL. So as far as inertia goes there is no problem since its only spacetime itself that is causing the effect. If you expand any system or geometry over time it grows faster and faster. Eventually such growth results in its size increasing faster than light can travel. But such geometric growth does not violate anything out of relativity. If anything it only sets a limit on how much of spacetime we can view at anyone point in the history of the universe. With accelerated expansion eventually only things very local will be able to be viewed.

[Qfwfq]

Jay-qu said:

do you think there is a material dense enough that it would be instantaneous or at least faster than light?

It would have to be a material in which the particles are bound by a field that could propagate faster than light. The fields we know of don't.

In essence, if you can't find a field that propagates faster that light, you won't find a material that get's around the limitation.

If you do find one, hope remains for that jackpot... now stands at €53 million.

[TeleMad]

Aki said:

I briefly read this month's Scientific American, and it says that galaxies can recede faster than the speed of light, and that this does not violate special relativity.

Right, because the galaxies are not moving through space faster than c; they're "riding" the expansion of space (and with so much intervening space between them and us that is expanding, they are receding from us superluminally). To avoid this possibility is why I added as my third qualifier "Third, I assumed the motion was through space."

[Jay-qu]

but that assumes you take space as only the three spatial dimensions that we spend every day life in. Because the universe is expanding it has to be expanding relative to something - say the 5th dimension (taking the forth as time) - So could you then say it is possible for something to travel faster than light if higher dimensions are included...

[C1ay]

Jay-qu said:

Because the universe is expanding it has to be expanding relative to something...

Why does that something have to be anything other that itself? When a balloon expands each oh the points on it moves away from all of the other points on it regardless of it's surroundings. There does not need to be some external measure of expansion for expansion to occur.

[NomadaNare]

I saw somewhere earlier that if something moved faster than light it would observed as moving backwards. Well I've heard descriptions of positrons being just "electrons moving backward in time" and they are almost massless so... . I have often pondered this question though. But what Im wondering is what if there is something already moving faster than light and we just can't detect it. Maybe "dark light" having something to do with dark matter. idk just random spouts of me brain.

[Tormod]

Welcome, NomadaNare. Very nice avatar!

[maddog]

NomadaNare said:

I saw somewhere earlier that if something moved faster than light it would observed as moving backwards. Well I've heard descriptions of positrons being just "electrons moving backward in time" and they are almost massless so... . I have often pondered this question though. But what Im wondering is what if there is something already moving faster than light and we just can't detect it. Maybe "dark light" having something to do with dark matter. idk just random spouts of me brain.

NomadaNare, I think you are talking about Positrons. It is these particles that would behave as you
say. A Positron is actually the Antimatter partner of an electron. Were an positron and an electron to
meet they would annilhilate each other and produce two Gamma Rays moving away from the center of
the explosion in opposite directions.

Maddog

[NomadaNare]

I was also thinking about the question on my way home. Doesn't E=mc^2 imply that if something has energy is has mass? Well, light is energy, which implies that it has a mass even if it is a miniscule amount, right? My insight into the equation is very limited so if one could clear up this misconception, i would appreciate it. O and thanx tormod.

[Jimoin]

A modification on the pole question, instead of pushing it, how about spinning it?

If I had a really long pole, were able to pick it up like a baseball bat and spin around, what's stopping the end of it breaking c? It doesn't rely on collision effects because each particle is only moving in relation to each other, not space.

[maddog]

NomadaNare said:

I was also thinking about the question on my way home. Doesn't E=mc^2 imply that if something has energy is has mass? Well, light is energy, which implies that it has a mass even if it is a miniscule amount, right? My insight into the equation is very limited so if one could clear up this misconception, i would appreciate it. O and thanx tormod.

This is one of the many odd things about QM. Yes light or particle version called a
photon has energy. Yes, a photon is a massless particle (no mass). Yes, E = mc^2.
Yes, this doesn't agree. I know it is odd. The mass you would be thinking of in the
above equation is a "rest mass" or the mass at rest. Well, the photon or wave of
light is always in motion and never still. This is called propagation or radiation of
the light. I hope this clears it up.

Maddog

[maddog]

Jimoin said:

A modification on the pole question, instead of pushing it, how about spinning it?

If I had a really long pole, were able to pick it up like a baseball bat and spin around, what's stopping the end of it breaking c? It doesn't rely on collision effects because each particle is only moving in relation to each other, not space.

The problem is here you "pole" is made up of atoms. Atoms are only loosely bound
together even for a solid. Stresses on the pole will prevent the pole from being very
long at any speed let alone relativistic ones.

Maddog

[Jay-qu]

Yet another mod to the pole question...

What if it was a disk?

[Qfwfq]

Pole or disk, even if you avoid breaking it, even if you recite the right mantra, to get the furthest parts of it moving at a velocity approaching c you would have to supply a kinetic energy approaching infinity, wich means you would have to do an amount of work approaching infinity.

[Qfwfq]

NomadaNare said:

Doesn't E=mc^2 imply that if something has energy is has mass? Well, light is energy, which implies that it has a mass even if it is a miniscule amount, right?

Unfortunately NomadaNare, there has been a lot of confusion around since Einstein's pubblication of 100 years ago. It is, to a great extent, a matter of terminology.

Think of mass as being energy, not as what something has besides energy. In modern terminology, mass is a shortcut for saying "rest energy". When moving, a body will have a kinetic energy as well as the rest energy and the total of these is often called the mass of that body at that velocity, but this type of statement is a misconception that has created a lot of confusion.

A photon has no mass and therefore it has only kinetic energy, which also bears the consequence of its velocity being exactly c. This kinetic energy is proportional to frequency, a fact that had been gleaned from the photoelectric effect not long before SR was worked out.

If the moving body is part of a composite object, this will have a mass (rest energy) which includes the moving part's kinetic energy, just as it will include potential energies of forces between its parts. Only in this way it makes sense to regard the kinetic and potential energies as also being mass; they contribute to the rest energy of the composite body. Not to the rest energies of the single bodies that are moving, or attrating and repelling each other.

The misconception of mass = m_0 over gamma was introduced the year following Einstein's publication when these things were still poorly understood, it should be considered a relic of history, a half baked thing, neither fish nor fowl. Instead it is still taught, all to much, as being an essential fact of SR.

In the appropriate Lorentz-covariant way of things a body has a mass, which is a scalar quantity not dependent on its motion but I won't go into detail because I don't know if you are familiar with the 4-vector formulation of these things.