Thread: Passage of time,the of speed light, and Reletivity

On almost every Discovery networks, History Channel, Or PBS show I see about outer space, they almost always go over relativity and light speed. They say that time is relative to the observer, and thy use the same stupid analogy on every show.

"Spaceman Bob goes the speed of light for one year, comes back, and earth has aged
50 years"

.......then they stop explaining why and say "Because time is relative, see?" Then they move on. Thats not a very good answer if you ask me. Leaving me on my couch, swearing at my TV. It's an example of relativity, sure, but one that opens the door for other questions.

I also saw a segment on a show(I think it was The Universe w/ Stephen Hawking on Sci channel) and they were talking to a guy that works at a detection station for particles that enter the earths atmosphere but get (destroyed/evaporate) within a thousandth of a second.(I don't think it was wimps) So, if they get destroyed so fast they would all be in the upper atmosphere and undetectable on the surface. But this guy shows that his detector is getting hits from these particles, and he says that it's because they're traveling at the speed of light, so time goes slower for them, so they decay slower......something along those lines. I like this example alot better.

I understand the concept of relativity.(not the math) I understand that as you approach the speed of light time slows down.(I think) But what I don't understand is what speed has to do with the space-time continuum. I don't know why time slows down for spaceman bob. I know that space-time can be warped by gravity/mass, but by speed as well? Can someone shed some light on this?

How does speed affect the passage of time?
Why does time seem to slow down?

I think it has to do with the speed of light being constant. If you are standing still and I am on a train travelling at 3/4 the speed of light away from you then you would expect that the light from a flashlight I was holding would be travelling 1 + 3/4 the speed of light away from you, but it doesnt ... it travels at exactly the speed of light away from you. I being on the train see it travelling at exactly the speed of light away from me. In order to make these both correct time has to be flowing at different rates for you and I. Time is relative, Space is relative and the speed of light is always constant.

Originally Posted by Joe McCarron

On almost every Discovery networks, History Channel, Or PBS show I see about outer space, they almost always go over relativity and light speed. They say that time is relative to the observer, and thy use the same stupid analogy on every show.

"Spaceman Bob goes the speed of light for one year, comes back, and earth has aged
50 years"

.......then they stop explaining why and say "Because time is relative, see?" Then they move on. Thats not a very good answer if you ask me. Leaving me on my couch, swearing at my TV. It's an example of relativity, sure, but one that opens the door for other questions.

I also saw a segment on a show(I think it was The Universe w/ Stephen Hawking on Sci channel) and they were talking to a guy that works at a detection station for particles that enter the earths atmosphere but get (destroyed/evaporate) within a thousandth of a second.(I don't think it was wimps) So, if they get destroyed so fast they would all be in the upper atmosphere and undetectable on the surface. But this guy shows that his detector is getting hits from these particles, and he says that it's because they're traveling at the speed of light, so time goes slower for them, so they decay slower......something along those lines. I like this example alot better.

I understand the concept of relativity.(not the math) I understand that as you approach the speed of light time slows down.(I think) But what I don't understand is what speed has to do with the space-time continuum. I don't know why time slows down for spaceman bob. I know that space-time can be warped by gravity/mass, but by speed as well? Can someone shed some light on this?

How does speed affect the passage of time?
Why does time seem to slow down?

yeah, actually , that does help. It fills in some gaps. I'm gonna bump the thread and take some time to wrap my head around that, and come up with an intelligent response. this aint ova.

Originally Posted by Joe McCarron

yeah, actually , that does help. It fills in some gaps. I'm gonna bump the thread and take some time to wrap my head around that, and come up with an intelligent response. this aint ova.

Draw out the train scenario. speed of light ( change in distance / change in time ) needs to be equal in both scenarios. Since the person on the train is moving ... their time needs to be moving slower and their space needs to be compressed relative to the person standing still so that the speed of light is equal.

You also mentioned gravity. One thing to remember is the equivalence principle. A person in an elevator can not tell the difference from being in a gravitational field OR accelerating in the opposite direction.

It has a lot to do with some of the equations and work within relativity. Turns out that if you added up your velocity both through space AND time it would be at the speed of light, so as your motion through space is increased, your motion through time decreases. This is why particles moving near the speed of light decay more slowly than particles that are at rest. This is also why if spaceman Bob goes out the the Andromeda Galaxy and back (at the speed of light) that he won't age at all, but if he had friends he will come back to a planet 5 million years older and they will all be long gone. So time is relative to the observer because of this (more or less).

Originally Posted by Joe McCarron

I understand the concept of relativity.(not the math)

My question would be, do you want to understand the maths, or do you prefer your current mode of understanding? I can run through the spaceman bob example and explain exactly what goes on, using the maths. If you don't like that approach, some of the other folks here would probably do a better job explaining it than I would.

Originally Posted by Joe McCarron

I understand that as you approach the speed of light time slows down.(I think)

Yes, as seen by others. You do not perceive time slowing down yourself; to you, everything seems perfectly normal, and it is the rest of the universe (which is moving relative to you) that is behaving strangely.

Originally Posted by Joe McCarron

But what I don't understand is what speed has to do with the space-time continuum. I don't know why time slows down for spaceman bob.

I don't know if anyone really knows why; we can describe how it happens, but as for why, I don't think we have an answer better than, "that's just the way it is". But I think you are really looking for the how of the situation.

Originally Posted by Joe McCarron

I know that space-time can be warped by gravity/mass, but by speed as well? Can someone shed some light on this?

How does speed affect the passage of time?
Why does time seem to slow down?

If you are moving relative to me, what is space to me, is a combination of space and time to you, and what is time to me, is a different combination of space and time to you. I would describe what speed does as not warpage, but rather rotation. If you want to take the mathematical approach, I can show exactly how it works; if you prefer a more intuitive approach, it would probably be best for me to shut up and let some of the others handle it.

One thing to remember is that the speed of light is just a ratio of change in space to the change in time ... for the speed of light to stay constant which per einstein it is ... space needs to warp proportionally with time. You cant just warp time otherwise the speed of light would not stay constant.

This is pretty fascinating you guys, thanks. I think i'm getting it now. To the observer, the lightspeed always has to be lightspeed. And for an object traveling at near light speed, that would mean that time must be slowing down for them.

Originally Posted by Joe McCarron

This is pretty fascinating you guys, thanks. I think i'm getting it now. To the observer, the lightspeed always has to be lightspeed. And for an object traveling at near light speed, that would mean that time must be slowing down for them.

Hah ... but now that you think you got a handle on it ... please read about the twin paradox ...
Because the passenger on the train thinks that we on the ground's time is running slower also. See the train is moving away from us .... but to the person on the train we are moving away from him .... so both people see the others clocks running slowly ... it is only until one accelerates to return to rendezvous can they compare the clocks and see which twin has aged more.

It is better worded here:
Twin paradox - Wikipedia, the free encyclopedia

Originally Posted by Joe McCarron

This is pretty fascinating you guys, thanks. I think i'm getting it now. To the observer, the lightspeed always has to be lightspeed. And for an object traveling at near light speed, that would mean that time must be slowing down for them.

Agree with Tom above, but just wish to emphasize - if a spaceship is travelling close to the speed of light (relative to us), we would observe that time has slowed down for the people on the spaceship. But for them, everything seems perfectly normal on the spaceship, relative to them, it is us moving (in the opposite direction) moving close to the speed of light, and they see time slowing down for us.

Tom references the twin paradox, and the resolution to that one has to do with the fact that one of the twins accelerates, and the other doesn't.