Going the Speed of Light

[Ellis]

If you could travel on a light wave from the sun to the earth, how long would it take you?

8 minutes (maybe 7, I don't remember). So your trying to say that the light itself takes 8 minutes. But if your on the light it's much slower?

We've already verified SR, is that your final answer?

 

[xXdaveXsuperstarXx]

We've already verified SR, is that your final answer?

Um, yes? Why?

 

[Ellis]

We've already verified SR, is that your final answer?

Um, yes? Why?

Because it's wrong, in more ways than one. I wanted to give you a second chance. Sorry, I'm not here to argue or debate 100+ years of physics research, so I won't go much further. I was trying to propose an easy question that would help you think about it. The answer was no time, not ~8 minutes or "much slower" than 8 minutes. You should take a physics class in the future, it's fun stuff.

 

[shelley]

I've been a TA for a relativity/quantum class for the past few weeks. xXdaveXsuperstarXx, just shut up and do some research before you embarrass yourself further.

It's true that none of us can travel at the speed of light. However, here's a real life example that illustrates time dilation: Muons are electron-like particles emitted from cosmic rays. They travel at relativistic speeds and have a short half life, such that without relativistic effects they would decay less than a kilometer after entering the earth's atmosphere. However, they do manage to reach the earth's surface due to time dilation (because they are traveling so fast, time passes at a different rate for the muon compared to observers on earth).

When you deal with relativity (very fast things) and quantum mechanics (very small things), there are many counterintuitive results. Relativistic time dilation has been mentioned, there is also relativistic length contraction, which makes things even weirder. But I'll let you find out about that one yourself (look up the pole-barn paradox). You can't just say "this is impossible, based on the experience of things I've observed," because nothing in our realm of experience can prepare us for the physical behavior of things that are that small or moving that fast. It seems illogical, but only because our logic is based on our experience of macroscopic, slow moving things.

 

[arud45]

Time is relative to your position, it's different based on speed. Someone else going the speed of light has no affect on you, and it would seemingly have no affect on them. But when you compare the two, they differ.

anyway, with today's technology/theories it is impossible to speed something up to the speed of light because it would take an infinite amount of energy.

 

[brunson]

GPS works because every satellite carries a highly accurate atomic clock and these clocks allow the satellites to know where they are in relation to each other with great accuracy. However, because the satellites are travelling at such a high speed relative to the earth calculations must take into account relativistic time dilation in order to remain accurate.

Short form: The clocks on the satellites run slower than if they were on the ground. It's a fact, it's been measured, Einstein was right. Just because it isn't "logical" to you doesn't make a difference.

 

[peterbat]

When you deal with relativity (very fast things) and quantum mechanics (very small things), there are many counterintuitive results.

Oooo, please elaborate. QFT FTW!

EDIT: I think this thread is ready to turn into the "Loop Quantum Gravity" thread, don't you? :rolleyes:

 

[daniel0731ex]

if you travel at the speed of light and met another person traveling at the speed of light
in an opposite direction, the relative speed would still be the speed of light

 

[JBCM627]

Thank you Shelley...

The best analogy I've heard to describe special relativity:

Consider two people sitting across the table from each other. A block is set on the end of the table. Person A observes that the box is to the right, and person B observes that the box object is to the left. But how can the box object be both to the right and left?

Special relativity "paradoxes" are no more complex than this - two people observing the same thing from a different point of view. Note that I put paradox in quotes... they aren't actually paradoxes.

More technically, both people at the table see the projection of the box into a flat, invariant, 2d (or 1d if you constrain it) euclidean space. Relativity is the analog of this - but instead deals with an invariant hyperbolic (non-euclidean) spacetime. We only see the projection of objects in this 4d spacetime onto our euclidean space, which is why we see apparent "paradoxes".

 

[Kyle™]

Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.

 

[FredM]

Ok. I had also the problem when imagining what happens with Relativity.

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?

 

[brunson]

Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.

No they aren't, that would violate special relativity.

If you fire two projectiles in opposite directions at non relativistic speeds, you can compute their relative velocity by summing their speeds relative to you, e.g. 700fps + 700fps = 1400fps.

That doesn't work for relativistic speeds. If each object is travelling away from you at 3/4 the speed of light, they are *not* travelling apart from each other at 1.5 times the speed of light, that's impossible.

 

[Kian]

Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.

False.

A basic rule of the universe is that anything without mass is traveling the speed of light, anything with mass is traveling at something less than that. Galaxies are not traveling at the speed of light.

Edit: Brunson explained the galaxy issue more thoroughly, I didn't see it when I posted.

 

[Ellis]

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?

No. If a star is 4 light years away, there's no way anything is getting there in faster than 4 years (or in 4 years unless it is light itself).

 

[Kyle™]

Completely False kian.

 

[brunson]

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?

No. If a star is 4 light years away, there's no way anything is getting there in faster than 4 years (or in 4 years unless it is light itself).

From an external observer's point of view. The ship were to travel at near light speeds the passage of time to the occupants would slow so it would seem less than 4 years.

 

[4Chan]

Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.

I assume this is what you mean by "traveling apart"

As quoted from wikipedia:

Universal expansion

The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies.

In these examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity.



What i learned about mass was that, due to "length contraction", nothing past a certain mass can exist past the speed of light.

Also quoted from wikipedia:

An observer at rest viewing an object travelling at the speed of light would observe the length of the object in the direction of motion as zero. Among other reasons, this suggests that objects with mass cannot travel at the speed of light.

Im not sure what youve learned, but thats what i learned.

Also, i am also aware of relativistic particles such as neutrinos and cosmic rays traveling near the speed of light. as shelley stated.


EDIT: by the time i finished my reply, others had already replyed. (x

 

[brunson]

Completely False kian.

No, completely true.

http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html

 

[Ellis]

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?

No. If a star is 4 light years away, there's no way anything is getting there in faster than 4 years (or in 4 years unless it is light itself).

From an external observer's point of view. The ship were to travel at near light speeds the passage of time to the occupants would slow so it would seem less than 4 years.

Well yea, oops. Even after the question I posed earlier

I don't know why I was thinking external reference.

 

[shelley]

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?

No. If a star is 4 light years away, there's no way anything is getting there in faster than 4 years (or in 4 years unless it is light itself).

From an external observer's point of view. The ship were to travel at near light speeds the passage of time to the occupants would slow so it would seem less than 4 years.

Well yea, oops. Even after the question I posed earlier

I don't know why I was thinking external reference.

To be fair, he didn't specify a frame of reference.