time travel

I am in deep regret over one day, trivial as it sounds, I need to go back

Will time travel ever exist?

It changes by quite a bit. If you travel at 0.9c, time passes ~2 times faster relative to you. At 0.99c its ~7 times, 0.999c is ~22 and 0.9999c is ~70.


And yes, sort of. That's length contraction. If something is moving, relative to you, then the object appears to be smaller. Relative to that object however, it remains the same size and its you that's smaller.

When he said more massive, I think he was referring to its energy, not physical size.

Relatively speaking, you could travel forward in time faster. Time Dilation means that as you approach the speed of light time moves slower relatively to you.

So if you you have person A and B; person B remains on earth, person A goes around and flies in his spaceship at the speed of light. Relative to person B, time moves slower for person A. This means that when Person A lands back in earth, he would have perceived less time than person B perceived so technically he would've traveled to the future. It's impossible to travel back in time I think, apart from something random I read a while ago about wormholes.

It changes by quite a bit. If you travel at 0.9c, time passes ~2 times faster relative to you. At 0.99c its ~7 times, 0.999c is ~22 and 0.9999c is ~70.

Ah, thank you for the explanation! Point taken & rep given

About the shrinking of objects when they move faster - If i remember rightly: Einstein gave an example of a car which is 4m wide, and said for it to fit into a garage which is 3.9m wide, it would have to travel just over 22% of c. If the object does not change size relative to itself, how does it work? Does it still shrink relative to the garage?

I don't know if you have a source for that but to me, if it doesn't fit in at rest then it won't fit in at any velocity. However much the car is length contracted in the garage frame to fit through, the garage is length contracted by the same amount in the cars frame, stopping it fitting

Well, I read it in Brian Cox's book - 'Why does E=mc^2? And why should we care?'. Surely if the car shrinks relative to us, it would shrink relative to the garage too? - as the garage is at rest like us.

Ah, thank you for the explanation! Point taken & rep given

About the shrinking of objects when they move faster - If i remember rightly: Einstein gave an example of a car which is 4m wide, and said for it to fit into a garage which is 3.9m wide, it would have to travel just over 22% of c. If the object does not change size relative to itself, how does it work? Does it still shrink relative to the garage?

It might be at rest to us but it's not at rest relative to the car

This is actually a very good question. Let me use my own example if you will (its actually a common example used)

Consider a barn of length 15m and very far away is a pole of length 20m. Now a friend stands at the front of the barn and you pick up the pole a long way away. Now as it stands, you both agree that the pole can not fit in the barn. (This is a very important point, all (inertial) observers must agree on the laws of physics, or in this case that the pole cannot fit in the barn.

You now run towards the barn at 0.8c. Now let's look at the viewpoint of your friend stood at the barn. He sees you coming towards the barn at 0.8c. Due to length contraction (going through the calculation), your friend sees that the pole is now 12m in length. So from his viewpoint the pole can now fit in the barn, with 3m to spare. You then reach the barn and he closes the door once you're all inside.

Now look at the viewpoint of you running. You're running with the pole. So you see that still at 20m. However, you see the barn approach you at 0.8c, so by length contraction the barn seems even shorter, now at 9m long. So according to your viewpoint you cannot possibly fit in the barn. However, your friend has closed the door on the barn and you're inside. You both MUST agree that you're inside. So what has happened?

I'll leave that for you to ponder on

A good example! They definitely contradict each other! Are you saying that he definitely got inside the barn?

A good example! They definitely contradict each other! Are you saying that he definitely got inside the barn?

Yes there certainly seems to be a contradiction! But there is a way to resolve this and explain how you and your friend both see that you're inside the barn.

Hmm. I'll have a good think about it before I click your spoiler! will it require knowledge above GCSE level to figure out?

Should be fine for GCSE! You'll need to know that "information" travels at the speed of light. As for the calculations, some simple speed equals distance over time.

I am in deep regret over one day, trivial as it sounds, I need to go back

Will time travel ever exist?