looking back in time

[patty-rick]

im new to all this so please dont cut my down to fiercly in frenzy of intellectual mumbo.

if i was to place a mirror out in space 1 light year away. Would i then be able to sit on earth and 2 years after it appeared there be able to see the past occuring, in real time???
of course this relys on a few impossible aspects, like getting a big enough mirror 2 light years away, but if that is presumed would it be possible to do so??

[MacM]

Patty Rick,


Actually you can do that now. Stand 4 feet 11 inches from a mirrow and you see yourself as you were 1/100,000,000 of a sec younger!

[ryans]

Why not use a video recorder instead, its cheaper than sending a rocket 1-light year away?

[patty-rick]

wow even better way of looking at it MacM hmmm also another question....

nothing can travel faster than the speed of light correct??? as that is asymtotic on a graph of energy to speed..
speed is all relative to a stationary point therefore

if you have 2 objects travelling towards each other at 0.6 C what is there relative velocity 1.2C i would imagine but how does that work?

[MacM]

patty-rick,

Per Relativity (Velocity Addition Formula) the collective speed is only 0.88235 c.

Why not use a video recorder instead, its cheaper than sending a rocket 1-light year away?

Yea, you can wait 10 years, watch the video. Not bad ryans.

[patty-rick]

Per Relativity (Velocity Addition Formula) the collective speed is only 0.88235 c.

can u explain???

[Xlock]

Resultant velocity of two bodies in special relativity is V=(u+v)/(1+u*v/c^2)

V=(.6c+.6c)/(1+.36c/1c)=.88235c

[patty-rick]

y is that so though, how is jsut a formula derived, surely to objects travelling past each other at speed 'x' have a relative velocity of '2x'

[James R]

patty-rick:

The formula is derived from the Lorentz tranformations of special relativity.

[Xlock]

patty-rick:

If you want more to read on the subject you may go here:
http://theory.uwinnipeg.ca/mod_tech/node137.html

[patty-rick]

i guess its one of those things that im going to have to accept , too fair ahead of me some of that stuff, just doesnt logically work in my mind

[HallsofIvy]

patty-rick: Could you explain to us why you think that two objects moving toward each other, each having speed x relative to something between them, would be moving toward each other a speed 2x?

In other words, WHY do you think that speeds add in that simple way?

[jcsd]

Well HallsofIvy it's not a completely unreasonable assumption if you don't know anything about Special Relativity, it's how they add up in Newtonian physics and very good approximation for what happens at non-relativistic speeds.

[Persol]

Because that's the way it works if v is small. People just assume that it works at all velocities.

[patty-rick]

exactly , i have read through the time dilation and length contraction and i understand the effect of not reaching 1.2c, but my first observation was by no means unreasonable just a little un educated as you appear to be if you not familiar with those newtonian physics laws