Relativity Question

[Paul98]

Your calculations are off because of quite a few things. As he said above one is due to you mixing frames of reference.

Ok so you have each ship moving away from a mid point in opposite directions at .6c. This means in each ships frame of reference the other is moving away at, as I Said before .882c. That number I calculated earlier from the speed addition formula.

I am not just talking what one ship might see at the other ship. I am talking what actually happens in the frame of reference of one ship compared to the other ship.

Do you agree with this?

 

[TastesLikeChicken]

I am not saying that. I am telling it as it is.

My example does take it from the POV of a guy on the ship. Read through it. The places each ship appears to be based on how long it would take the light to get from one ship to another when it passes a particular point.

The 3 and 6 second points on the observers ship would be the places where the other would appear to be at 1 and 2 seconds (with 2 and 4 seconds lag due to travel time of the light). They will see, using light as the transmission media, those distances at those times. IOW, at T=3 seconds, the light from the other ship from T=1 would just be reaching it....

Now add the time slowing effect...

Let me explain it a bit more fully to show you where you mistake is and why you are not considering the proper reference frame.

You are considering each ship's position from an outside frame of reference - the point of departure. What someone on the ship would see is different. Consider the 3 second differential. The light arriving at each ship in 3 seconds would show the other ships position from 3 seconds previously when, in actuality, both are truly further apart. Each ship would make a calculation based on the positions observed in their frame of reference, not the positions that would be observed by someone at the point of departure.

To futher explain it, consider that every picture we see of galaxies is actually a bit of a lie. We are seeing their positions from millions or billions of years ago when, in reality, they are much closer or much further away since they have moved in the time that light has taken to arrive for us to observe them.

 

[PlasmaBomb]

So one ship travels out at .6c, the light coming out the back of the ship will travel at c from the rear of the ship, it would be observed moving away at 1.6c (it IS additive) but not MOVING faster than c....

This is wrong and has been proven to be so for quite some time...

http://en.wikipedia.org/wiki/James_Bradley
http://en.wikipedia.org/wiki/Aberration_of_light
http://en.wikipedia.org/wiki/Parallax

One would assume if things were additive that when you measure the speed of light from distant stars that when the earth was moving towards them the speed of light would be (c+v) and when the earth was moving away from them its speed would be (c-v), however in both cases the speed of light reported is c.

 

[IHateMyJob2004]

We are moving probably at mutlples of the speed of light relative to some object that is 100s of light years away. Think about it ...

 

[Ninjahedge]

OK, so two ships travelling away from each other at .6c (each, not additively) will somehow magically travel slower than light away from each other.

Nobody has done a single math problem where both ships start out at "0" and move away from each other, each traveling at the speed of light, but whatever.

Pointless.

Again, look at the math. Assuming they are both at a universal 0 mph. One startes going 0.6c to the left, the other starts going 0.6c to the right. They are seperating at 1.2c, period.

Now, if you do the math and see how long it takes light to get from one ship to another, not additive, simply travelling at c in relation to the absolute stationary point of the universe, the light has to travel a bit longer to close the distance.

If they are both travelling at .6c, they are 1.2 light seconds apart at 1 second. The light leaving one ship will take 1.2 seconds just to get to where the other ship is at that moment. 1.2 seconds later, the other ship has moved another 0.72 light seconds. .72 seconds later, it has moved an additional .432 and so on, until the light finally catches up to it at T=3 seconds.

So, at T=3 seconds ship #2 sees where ship #1 was at 1 second.

Ship #2 is at 3 x 0.6 = 1.8 light seconds. Ship #1 was at 0.6 light seconds.

1.8 + 0.6 = 2.4. Ship two, if there was no time distortion, would see ship one moving away at 2.4/3 = 0.8c.

Now take time slowing down. That formula I mentioned, is that the one used for relativistic time distortion, or is it one that only associates the grometric distortion of velocity (perceived to actual)? It calculates the distortion to be 1.25.

Slowing time down by that makes the 0.8 seem to speed up to c.

Trying 0.8c would yeild an 8 second time for ship two to see where ship one was at 1 second. 0.8 x 9/8 = 0.9c.

The Lorentz factor (1/(1-v^2/c^2)^0.5) comes out to 1.66666666....?

That does not make any sense. Slowing of perceived time by 1.666666 would make the .9c seem faster than light......

Again, is lorentz the time dialation factor?

 

[Paul98]

OK, so two ships travelling away from each other at .6c (each, not additively) will somehow magically travel slower than light away from each other.

Nobody has done a single math problem where both ships start out at "0" and move away from each other, each traveling at the speed of light, but whatever.

Pointless.

Again, look at the math. Assuming they are both at a universal 0 mph. One startes going 0.6c to the left, the other starts going 0.6c to the right. They are seperating at 1.2c, period.

What you are saying is that you don't believe in relativity.

 

[DrPizza]

OK, so two ships travelling away from each other at .6c (each, not additively) will somehow magically travel slower than light away from each other.

Brilliant! That's the first correct thing you've said! Except, it's not magic. If you lived 120 years ago & published this result and mathematically justified it before Albert Einstein did, you would have been famous.

 

[Ninjahedge]

I'm sure.

They will be in two places at the same time.

K.

 

[Paul98]

I'm sure.

They will be in two places at the same time.

K.

http://www.youtube.com/watch?v=wteiuxyqtoM

 

[QuantumPion]

We are moving probably at mutlples of the speed of light relative to some object that is 100s of light years away. Think about it ...

Not hundreds, but billions perhaps. But this is due to hubble's law and the expansion of space, not simply relative motion.

 

[DrPizza]

I'm sure.

They will be in two places at the same time.

K.

Time? Did you say time? Ahhhh, that's why you don't understand relativity.

 

[TecHNooB]

the 'slowing of time' and 'shortening of distances' thing always confused me. i wasn't sure if they occurred together, or were separate such that you could think of relativity in terms of one or the other.

 

[Paul98]

the 'slowing of time' and 'shortening of distances' thing always confused me. i wasn't sure if they occurred together, or were separate such that you could think of relativity in terms of one or the other.

Both things happen, lets say I am on earth and there is another planet that isn't moving with respect to me and it's 1 light year away. If there was a spaceship flying past the earth to this other planet at .5c. That planet is only .866 light years away from the frame of reference of the ship.

Also since it's all relative the slowing of time happens to both the ship and the people on earth depending on the frame of reference. So 5 seconds on earth might be 3 seconds on the ship from one frame of reference. Where as the other 5 seconds on the ship might be 3 on the earth. just depends which frame you chose.

 

[PlasmaBomb]

Today's XKCD...

Don't worry! From the light's point of view, home and your eye are in the same place, and the journey takes no time at all! Relativity saves the day again.