# Faster then c?

1. Mar 29, 2004

### The_Nebula

I heard a few things about going faster then c. But how would it really be achieved? I don't mean like tachyons or anything, maybe likejust before light reaches the event horizon it accelorates to beyond te speed? Is it possible at all? Some comments please, im curious and interested

2. Mar 29, 2004

In a word, "no."

In a few words, "there are lots of topics on the forums just like this already."

3. Mar 29, 2004

### The_Nebula

Sorry, i tried searching, but havent really encountered anything that was talking about this topic purely, i mean, i heard someting that Einsteins equations do not apply beyond the speed of light so you would not know. And something like you cannot accelorate to faster then the speed of light but you can go faster then the speed of light if you are already traveling it. Something like that

4. Mar 30, 2004

### billy_boy_999

i think there are also varying speed of light theories out there, i think alot of them have to do with 'inflation' in the very early universe, for a time the universe itself might have been expanding at faster than c...

5. Mar 30, 2004

### Janitor

How general do you want to get?

Take a laser pointer with you to the top of a hill. Point the laser out above the horizon and turn it on. Swing the laser pointer above your head, like you were going to lasso a steer, such that in one second the thing has rotated through a complete circle. If the photons in the laser beam happen to strike an object (the Moon, for instance) that is more than 1/(2 pi) light-seconds away from Earth, the set of events defined by the photons striking that object will propagate (if I may use that term) along the surface of the object at a speed greater than c. So if your understanding of "things" is broad enough to include that, then yes, there are things which can exceed speed c. Each individual photon from the laser moves at speed c, however.

Last edited: Mar 30, 2004
6. Mar 30, 2004

Or you could just imagine a "thing" in your head that goes faster than the speed of light. It saves you the cost of a laser pointer.

7. Mar 30, 2004

### Janitor

Amen, brother.

I'm a cheapskate.

8. Mar 30, 2004

### marcus

we are currently observing galaxies which were receding from us at speeds greater than c when they emitted the light which we are now getting from them

and as far as is known these galaxies continue to recede at speeds greater than c
their present speed is proportional to their present distance according to
the hubble parameter 71 km/s per megaparsec
if you take something that is currently over 13.8 billion ly away then multiplying that distance by the hubble parameter you get that its current recession velocity is greater than c

a good way to get acquainted with recession speeds in the standard model of cosmology is to use Siobahn Morgan's calculator
put in 0.27 for omega (matter)
0.73 for lambda (dark energy)
and 71 for the hubble parameter
and try a redshift z = 3, or 4, or 5

most of the observable universe was receding at greater than c when it emitted the light that we are now receiving
a URL for Siobahn's calculator is in the Astronomy Sticky Thread
(Astronomy and Cosmology references)

Ned Wright's tutorial goes over similar stuff

9. Mar 30, 2004

### marcus

Last edited by a moderator: May 1, 2017