Does time stand still at the speed of light?

[kerrywins]

For the object traveling at the speed of light...does time, relative to everything around him, stand still?

[Dudley_DUright]

1. This is a question that Einstein himself wondered about

however, it is not possible for something (or someone) with a nonzero mass to travel at the speed of light. It would take an infinite amount of energy to attain that speed. Only massless particles (like photons) can travel at the speed of light.

[kerrywins]

2. Does time stand still at the speed of light?

for photons...

[Dudley_DUright]

5. There is no inertial "rest frame" for photons

One of the basic postulates of special relativity is that all observers, no matter their relative motion agree on the speed of light. However, the frequency (and energy) of the photons does depend on the relative motion of the observer and the source via the relativistic Doppler effect (the famous red shift) that allows us to know that distance galaxies are moving away from us (hence the universe is expanding).

[baldguy]

3. Not quite...

At increasing relativistic speeds, time slows down with regards to an outside observer. But the mass of an object increases, and the amount of energy required to accelerate it increases - again to an outside observer. At the speed of light, theoretically mass would be infinite, the amount of energy needed to get it there would be infinite, but time wouldn't pass - again to an outside observer.

To a person MOVING at near the speed of light, they would experience the universe around them moving faster & faster. They wouldn't experience any change in themselves. At the speed of light, the UNIVERSE would move at infinite speed.

[Sir Craig]

9. I've never quite understood that premise...

I understand that the whole relativity argument is based purely on observers, that an observer on Earth (for example) witnessing a spacecraft heading away at speeds approaching the speed of light would observe time on board the spacecraft slowing, while those on the spacecraft would see no such time dilation.

Yet what bothers me is wouldn't the people on board the spacecraft, looking back on the earth, also view Earth's time slowing down? As this is all about observers, the earth would red-shift to those on the spacecraft just as the spacecraft would red-shift to those on Earth. Just because the spacecraft is providing the speed doesn't mean the apparent red-shifting of the earth won't be observable.

Also, what happens if the spacecraft approaches light speed but maintains an orbit around the earth? Does its time still become altered, and if so why? Is there a physical property to time that relativistic speeds would influence? Would it have something to do with the gravitational well that is created by the increasing mass of near-light speed objects, and again, if so why?

Damn my ignorance today...

[wtmusic]

4. And DU men--if you're insecure about your "size"

just accelerate yourself to close to the speed of light (facing the direction of travel). Your length will increase considerably, and you'll be quite popular with all the relativistic ladies!

[Dudley_DUright]

6. Just the opposite I am afraid

It is relativistic length contraction, not expansion that occurs. :-(

[wtmusic]

7. oops

now where's the receipt for that damn rocket...

[onebigbadwulf]

12. Both contraction and dilation occur

It depends on the perspective.


Let's say a rocket ship is traveling 99% the speed of light from LA to NY.

From the rocket's perspective, the length between LA and NY will contract. As my physics professor once said "You can make anything inches apart, you just have to be going fast enough"

From the earth's perspective, the rocket will appear miles long. The rocket, from the Earth's eyes, undergoes considerable length dilation.


Yes?

[Dudley_DUright]

13. Yes?

Nope. Your physics professor is correct, but from the Earth's eyes, the rocket would also be length contracted.

[aint_no_life_nowhere]

8. What I have always been told

is that if a person were able to somehow travel on a beam of light, that traveling anywhere in space, whether short distance or long, would be an instant journey within the personal experience of the traveler. That is, one would not experience the passage of time at all. It would be 'poof', I'm there, for any location within the universe. The clock hands of one's own clock during the journey would not have moved and our own biological perception of the passage of time would not have involved any movement at all (heart would not have pumped, lungs would not have moved, eyes would not have shifted). Therefore, I don't think you could say that time would stand still. I think that according to our biological perception, there would have been no time passing at all. I think this is why they say it is impossible to go faster than the speed of light, because relative to the light beam, it is instantaneous travel, even though the non-moving observer does note the passage of time during which light moves through the universe.

[kerrywins]

14. thanks...

I think agree with that way of looking at it...
i now understand a little more...

[Fuzz]

10. But would your headlights do anything?

Stolen from Steven Wright without permission.

[Ready4Change]

11. My theory:

If time were stopped at the speed of light, then light would travel from point to point in no time. However, time DOES pass during lights travel.

[No2W2004]

15. OK....time out for some Python....

Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.

Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.

The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.

[Aftershock]

16. In my readings of physics and astronomy books...

I have come to the conclusion that no one knows.

Few have suggested that time goes infinitely slow as one goes the speed of light. This has been hypothesized by studying black holes and what happens when light enters the event horizon.

It's impossible for anything with mass to go the speed of light, however, because you need an infinite amount of energy to make something with mass to go the speed of light.

It's all complicated (yet very interesting) stuff. I'm hoping to do more reading on the subject in the future.

If you want to know more on the subject, I suggest you read Brian Greene's book The Elegant Universe. It's written in layman's terms and it's very easy to read.

[JSJ]

17. dunno- but lightspeed is now considered variable