# The Speed of Lght and beyond!

#### Max

[SOLVED] The Speed of Lght and beyond!

Can, or have we ever gone faster than the speed of light?

What happens to the properties of something going faster than the speed of light?

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#### russ_watters

Mentor
Travel at or above the speed of light is forbidden by Einstein's relativity. As an object accelerates it gains mass, slowing the acceleration. So even an infinite amount of thrust for an infinite time will not get something there.

#### Max

Thats incredible!

Thanks! I am still mind tripping from the following:

As an object accelerates it gains mass, slowing the acceleration. So even an infinite amount of thrust for an infinite time will not get something there.

Wait a minute, just wait a minute..this means that Warp drive can never exist??? (Raises an eyebrow).

#### Jack

correct. As an object approaches the speed of light mass would become infinite and time would slow down to a stop.

#### marcus

Gold Member
Dearly Missed
Whenever people repeat the SR speed limit I believe they should make it clear that there are two sorts of velocity and only one is governed by the limit.
Otherwise people end up being confused.

The high redshift objects observed in astronomy are seen in the act of receding from us faster than light. The Astro magazine "Sky and Telescope" has a computer program for calculating the recession-speed from the redshift and an astronomy professor (S.M.Morgan) has made it available as a JAVA applet online for her students to use.

http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html [Broken]

From this you can easily calculate for example that a certain quasar (in Ursa Major) which was observed last year with redshift z = 6.4 was receding at 3 times the speed of light at the moment when it emitted the light which we are now receiving from it.

Most of the observable universe is receding at speeds >c
but this does not contradict "special" (i.e. LOCAL) relativity which concerns nearby objects in the same local coordinate patch and the speed at which information can travel.

GR does not obey the rules of local relativity (SR) in any simpleminded way. GR, for example, does not have the same kind of symmetry as a theory. So it is probably a bad idea for us to lay down the speed limit law without qualification, as if it were universally applicable

to say that the speed with which distant galaxies are moving away from us is not "really" speed because it is merely due to the expansion of space....well it is still a "time rate of change of distance", but it is not really a speed (!)
is one way to handle the verbal difficulty

But Davis and Lineweaver, in there short pedagogical piece "superluminal recession velocities" handled it by explaining at the outset by there are two distinct forms of speed.

However one decides to handle the verbal complication here, one ought not to just try to sweep it under the rug and ignore it.

That cosmology calculator is neat. Here is S.M. Morgan's homepage in case you want to see more about her.

http://www.earth.uni.edu/smm.html [Broken]

A working astronomer specializing in variables (Cepheids and others) who teaches at a Univ. in Iowa.

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