Weird things happen at speeds close to c...

[Nacelunk]

So I thought about something recently.When you move (in a super-fast spaceship) at speed close to c (say 285000 km/s) the time is slowing down relative to ouside the ship. So which means that while you are sitting there for a minute, there is actually, say, 20 hours gone outside the ship. So if you look at it and measure the distance that the ship travelled in 1 second, it wouldn't be 285000 km. It would be much less. So the paradox is - the faster you are trying to move, the slower you are actually moving. Am I right? If yes, how can it be?? It doesn't make any sense!

Also I have some other questions - what is the fastest possible speed we can really reach (on a spaceship)? And also isn't that time traveling? And also where does the mass come from when you reach light speed? It can't just appear from nowhere! And finally - why does the time slow down (or speed up, depending on your point of reference)?

One more thing - suppose you travel in a space ship at 290000 km/s and you throw or launch something at speed of, say, 50000 km/s. Theoretically the speed would add up to 340000 km/s. What would happen in that case?

[[Tycho?]]

Firstly, take a browse around the relativity forum for older threads. Most of this stuff has been done to death.

 

I am going to approch this from the bottom up. When you add two very large velocities normal velocity addition does not apply. You can't just take .7c + .8c and get 1.5 times the speed of light. Instead there is relativistic velocity addition, which insures that the total speed does not exceed c.

 

This forumla works so long as you express velocity as a fraction of the speed of light. Ie half the speed of light is 0.5c.

 

Time slows down... because it does. This is not something I can easily explain to someone with no physics knowledge.

 

Ok, the mass increase thing. You have to be careful with this. In relativity, there are two terms for mass, rest mass, and relativistic mass. Rest mass is when an object is not moving, its the thing's "normal" mass. Rest mass never changes. Relativistic mass is the mass the object appears to have when it is moving at a large percentage of c. When you are going a large percentage of c, mass doesn't *really* increase, there are no more atoms or molecules than there were before. What you are adding however is kinetic energy. And since E=mc^2, this increase in energy has a corresponding increase in mass.

 

So, its rest mass is always the same. Its relativistic mass increases, because you are adding more energy in. So instead of saying the mass increases you might just say the energy increases and save some confusion.

 

The only absolute limit on the velocity of anything is c. No space ship could reach c, but one might be able to go 99.99999999% the speed of light. There are a variety of practical restrictions, like the efficiency of your drive, what you are flying though (moving at such a stupidly high speed just moving through intersteller space would be a radiation hazard due to blue shifting) and engineering stuff like that.

 

Your paradox is kinda backwards. To the observer on the ship, time moves as normal. You see the outside world moving more slowly. But you would not measure yourself to be moving more slowly, you would still see objects moving by you very quickly, and you could measure your speed via other means as well. However you are sorta on the right track. Along with time dilation there is length contraction. Meaning that not only do two observers disagree on what time it is, the also can disagree on how long something is. A person on a ship moving very quickly would observe another ship to be skinnier than it actually is.

 

Hope this helps.

[Nacelunk]

You see the outside world moving more slowly.

I thought it's vice versa. So you mean that if you move at 0.999 c for one minute and then stop, the clock outside the ship would show something less then a minute? What about twin paradox? It describes that that twin who flew at lightspeed didn't age as fast as his brother from the planet, meaning that the first twin went to the future. Am I right? If so then what you said

outside world moving more slowly

is supposed to be backwards. Isn't it?

[swansont]

I thought it's vice versa. So you mean that if you move at 0.999 c for one minute and then stop, the clock outside the ship would show something less then a minute? What about twin paradox? It describes that that twin who flew at lightspeed didn't age as fast as his brother from the planet, meaning that the first twin went to the future. Am I right? If so then what you said is supposed to be backwards. Isn't it?

 

 

Neither twin can absolutley seen to be moving; the resolution occurs because one of them accelerates, which moves him from one frame of reference into the other. While motion is relative, acceleration is not.

 

As long as the motion is inertial, each observer sees the other clock as running slow.

[Ragib]

ok if u still check this thread, hopefully u do, time slows down because say ur on earth, and ur frend is flying in a spaceship, at 0.9c. At high speeds there is a phemonenon called length contraction, in which things appear to be of less length. anyway, say the ship lets off a light pulse that goes to a mirror and bouces back, all inside the space ship. C is constant, they will agree on that, but they will not agree on the distance it is travlled. You on earth will think it has travlled less as the length has contracted. since you think the distance it has travelled is less, the time it has taken to get to the mirror and back is less. but the person on the ship will think its taken longer than u have. there u go, time dialation

[[Tycho?]]

ok if u still check this thread, hopefully u do, time slows down because say ur on earth, and ur frend is flying in a spaceship, at 0.9c. At high speeds there is a phemonenon called length contraction, in which things appear to be of less length. anyway, say the ship lets off a light pulse that goes to a mirror and bouces back, all inside the space ship. C is constant, they will agree on that, but they will not agree on the distance it is travlled. You on earth will think it has travlled less as the length has contracted. since you think the distance it has travelled is less, the time it has taken to get to the mirror and back is less. but the person on the ship will think its taken longer than u have. there u go, time dialation

 

Eugh, decent post, but could you try an improve your spelling, grammar and punctuation? Trying to read about relativity should be made as easy as possible, and proper sentace structure goes a long way.

[Ragib]

Lol. I am sorry, i'm not accustomed to typing like this . I'll try from now on.