How fast am i traveling???

del88

I've been reading a bit about einstein and can't get my head around something.......
How fast am i traveling....if i was to take of in a space ship i would be moving away from the earth at a given speed....lets say 2000mph....after a week i would only be moving away from the earth at that speed...all other objects is the universe would be moving at diffrent speeds..some towards,some at the same speed....at that point ....how fast am i traveling.
Einstein talks about traveling at close to the speed of light and how time slows....but How would he measure that speed ? Is it measured from the original fixed point in space/time??

oisin_t

its all relative! :pac:

lol honestly though...no idea..great question though! way to bamboozle peoples minds!

Tears in Rain

IANAP (I am not a Physicist), but as I understand it, the speed of light is always measured to be c = ~300,000km/s , no matter what reference frame you are moving in.

For example, say you are an observer in the same orbit as Jupiter. You are stationary relative to Jupiter, i.e. it never seems to move as you look at it (of course it rotates, but we'll ignore that). The light from Jupiter arrives to you at the speed of c, which is reasonable enough.

However, consider yourself as a traveler moving close to the speed of light directly away from Jupiter (from your point of view, Jupiter shoots away you near the speed of light, neither perspective is more right than the other). Light from the Jupiter still seems to reach you traveling at the speed c.

To make the apparent contradiction even clearer, imagine three spaceships, starting from the same point. One shoots off at the speed 0.5c , the other goes off in the same direction also at the speed 0.5c a few hours later. The third spaceship remains stationary. The first spaceship, some way into the voyage flashes his indicator lights. The second spaceship, traveling at the same speed and the same direction, observes the light signal, traveling towards him at the speed c. Some time later, as the light must travel, the third, stationary observer, observes the light pulse, also traveling at the speed c. Contradiction?

It's actually not a contradiction at all, as Einstein showed with his Theory of Special Relativity. The independence of the speed of light from the speed of the object emitting the light relative to a stationary observer was something that had been shown experimentally, e.g. in the Michelson-Morley experiment. However, people found it hard to reconcile this with their intuition and their knowledge of classical physics. However, Einstein showed (with lots of Maths) that really, there wasn't any contradiction, although a lot of things we held intuitively to be true in reality weren't. For example, whether two events are simultaneous depends on who's observing them, and time moves slower the faster you go.

So you're right to be confused about what is considered stationary and what is moving, it is a confusing subject, and it goes against many of our intuitive ideas. It's just something that you have to accept, no matter how wrong it seems, that the speed of light appears to be the same for all observers.

caveat: I'm not a physicist, so I might be completely wrong on some/all points, this is just from my understanding of the subject

Gurgle

del88 wrote: »

I've been reading a bit about einstein and can't get my head around something.......
How fast am i traveling....if i was to take of in a space ship i would be moving away from the earth at a given speed....lets say 2000mph....after a week i would only be moving away from the earth at that speed...all other objects is the universe would be moving at diffrent speeds..some towards,some at the same speed....at that point ....how fast am i traveling.

If you left the earth at 2000mph, and you haven't accelerated or decelerated since then you will still be travelling at 2000mph relative to the earth.

del88 wrote: »

Einstein talks about traveling at close to the speed of light and how time slows....but How would he measure that speed ? Is it measured from the original fixed point in space/time??

Pretty much, yes.
My understanding is that its the process of accelerating that causes time to slow down. While you're travelling at a constant speed time passes at a constant rate.
Then when you decelerate time speeds up again for you.

Gurgle

Tears in Rain wrote: »

To make the apparent contradiction even clearer, imagine three spaceships, starting from the same point. One shoots off at the speed 0.5c , the other goes off in the same direction also at the speed 0.5c a few hours later. The third spaceship remains stationary. The first spaceship, some way into the voyage flashes his indicator lights. The second spaceship, traveling at the same speed and the same direction, observes the light signal, traveling towards him at the speed c. Some time later, as the light must travel, the third, stationary observer, observes the light pulse, also traveling at the speed c. Contradiction?

c, the speed of light, is the same - but spaceships 2 and 3 won't see the same thing.

Number 2 will see the light flash its original orange colour as its travelling in the same direction and speed. It will also turn on and off in the same time frame as Number 1 observed.

Number 3 will see a red-shifted light which will turn on and off much slower than was seen by 2 or 1.

(Don't ask me to do the maths, haven't a clue where to start)

del88

So let me get this straight.......to me I'm never really moving...everything else is moving either away or towards me at different speeds and different rates of time as observed by me....ok
so my mass is always the same to me..... but if i could observe the mass of the traveling object it would increase to ME as it accelerates ...but to itself it would remain the same....but if it where to look back at me i would be to the one whose mass is increasing....i think..
Still thinking here.....dose that mean we would have the combined mass from the big bang caused by the acceleration from that point as viewed from that point in space time???
cheers for the replies...it's a very interesting idea..

Gurgle

del88 wrote: »

so my mass is always the same to me..... but if i could observe the mass of the traveling object it would increase to ME as it accelerates ...but to itself it would remain the same....but if it where to look back at me i would be to the one whose mass is increasing....i think..

The increase in mass is neccessary for conservation of momentum under time dilation.

But time dilation only happens to the accelerating body, not the static body... but the static body is accelerating relative to the accelerating body...

No idea.
Thats one for the 'real' physics forum

rccaulfield

You are moving at 2000 mph to a stationary observer. Thats it. The other objects are moving at 2000 mph or 1500mph to the stationary observer. MPH is a tool using a stationary observer.

Capt'n Midnight

You are moving 2000 mph relative to the point you left.

The earth will have moved on in it's orbit so you will no longer be moving 2000 mph relative to it.

You could decide that all motion is relative to the centre of the universe. The universe is expanding and if you work the expansion backwards then it turns out that the expansion is even and you can't actually tell where the universe is expanding from. So you can't find an absolute point to take every thing relative too.



Correct me if I'm wrong but can't we see the same distance in all directions back to near the big bang. ?