physics question

Einstein sad that nothing can exceed lightspeed. He also sad that all physic laws(so including the first thing he sad about light speed) stay the same equal what speed the observer has.

I do not get it. Because: I travel with almost light speed. I pass a planet, and and nearly immediately after, someone on the planet sends a light signal. It slowly comes nearer to my spaceship, and I catch it up. I send it out on the front of my ship, and if I’m right it would go with light speed away from me, and arives on the next planet in a time shorter than the light could travel from the first planet to the next. :-?

No …
the speed of your ship and the speed of light don’t add seen from the 2 planets. So they would see the first photon hardly reaching your ship and then you racing very close behind your emitted photon.
You on the space ship will also see photons with light speed. One came from a plantet which is moving at almost light speed away from you and one you sent to a planet approaching your ship with almost light speed.

BM

But…
If I’m in my space ship and test the light speed, it would not be the normal value. And einstein sad it doesn’t matter at what speed the observer is moving.

You may be making the same mistake I used to, which is thinking that this stuff is linear.

b01c

I can’t remember much of my Physics classes but I know that you can’t make light faster that way. Doesn’t the light just get doppler shifted to another frequency or something? Like what happens with sound waves at the front of ambulances.

Also, to put it a simpler way, the speed of light (in a particular medium such as the vacuum of space) is constant. “Launching” a light beam from a moving vehicle does not add the vehicles velocity on to the velocity of the light.

In addition, nothing in special nor general relativity prevents velocities above the speed of the light. What it prevents is accelleration (+ or -) to the speed of light (mass increases towards infinity; therefore, more energy is required to continue accelleration; at speed of light, mass is infinite, thus not enough energy in the universe to accellerate there). Above the speed of light, the math is pretty much just reversed.

And what about when I’m travelling in my ship from planet_A to planet_B at almost lightspeed, and I start running in my spaceship?

Well, you’d probably feel like Jabba the Hutt travelling that fast so I doubt you could run very far.

As you approach c (speed of light in a vacuum), volume also decreases toward 0. Therefore, running inside your spaceship (your current inertial frame of reference) would either:

a) Not be possible. If your FOR (frame of reference), i.e. your spaceship, were accelerating at anywhere near a significant amount toward c (say, 1000 miles per second per second), you would be smooshed into a pulp. And, as long as we’re talking about strict Einsteinian physics, there is no way to shield yourself from the forces generated by acceleration.

b) Progress would be insignificant. If you’re only accelerating at levels a human can withstand (say 8 earth gravities or so), you can still run (if you’re, like, the Hulk or something). But, say that you’re already at 99.9999% of c and not accelerating any more. Can you run that last 0.0001% and hit light speed? No - because although you just sprinted 60 meters inside your space ship in 5 seconds (wow! you’re fast), as far as an outside observer is concerned, you only just ran about 2 milimeters. Why? Because as things approach c, their mass approaches 0, along the axis of motion. In addition, as you approach c, time slows down (within your FOR) as well. So, while you just did the 60 m in 5 secs from your frame of reference, to a stationary observer, you just took three weeks to go 2 mm. It’s actually a lot, lot worse than that, but I don’t feel like doing the math right now. So, the closer you get to c, the more pronounced the effect becomes, until it takes you infinite time to run an infinitely small distance, meaning that you will never be able to run yourself past the speed of light.

This stuff is fun!

hehe i love physics :smiley:

But…

Not completely true. Everything is relative, and Einstein sad that if ex. you’re in a train, and you ( :stuck_out_tongue: VERY, VERY precise of course :stuck_out_tongue: ) measure the time from point_A to point_B (both in train) the light speed is normal.

if i remember rightly you also have the added problem of frequency doubling when travelling at the speed of light. when you travel into light at the speed of light the observed frequency of the light is doubled, therefore the frequency observed puts the light into the x-ray spectrum and would fry you…theoretically

how i always made sense of thigns is this.

as you increase speed your mass increases.

as mass increases (of atoms) their rate of vibration “decreases” similar to freezing somthing.

as the vibration decreases, time also dereases relative to the rest of people whos atoms are vibrating at a normal speed.

as for shooting a torch out he front of your ship, and that toch light traveling at light speed away from you, well i just never bothered understanding that, i think its all a bit of hoo har. (either that or my physics teacher never explained it well).

Alltaken

Time dilation.

The faster you go thorugh space, the slower through time you go. So, light would always pass you at the speed of light, because speed is dependant on time.
The equation:

t = time for the stationary person
to = time for the moving person
v = velocity
c = speed of light
sqrt() = square root

t = to/(sqrt(1 - v^2/c^2))

so as v->c

t = to/sqrt(0)
thus t tends to infinity.

Your mass increases as well, with almost exactly the same equation,
m = mo/(sqrt(1 - v^2/c^2))

That means your mass tends to infinity as well.

As you approach c (speed of light in a vacuum), volume also decreases toward 0.

Are you reffering to Lorentz Contraction?

Because as things approach c, their mass approaches 0

You mean size.

I do not get it. Because: I travel with almost light speed. I pass a planet, and and nearly immediately after, someone on the planet sends a light signal. It slowly comes nearer to my spaceship, and I catch it up. I send it out on the front of my ship, and if I’m right it would go with light speed away from me, and arives on the next planet in a time shorter than the light could travel from the first planet to the next.

Ok, since time slows down, the light does leave your ship at the speed of light to you, but not to a stationary observer.

Oh, to the other physics geeks like me :smiley: , when I say stationary, I just wanted to be concise and not pedantic, so dont bother complaining that you cant prove something is stationary and everything is realitive etc etc.

Ian

arrr now i get it.

that is what i was thinking.

Alltaken