How old is the light that hits earth?

[TobiasTheViking]

From the lights perspective that is.

I'm wondering because as far as GR goes, the closer we get to light speed, the slower time will pass for us.

It will take an infinite amount of time or mass for us to reach light speed. For some reason that makes me think that moving at the speed of light would mean that time would be infinitely slow(as in, not passing at all).

But..but.. aren't all the signal particles for the weak/strong/EM force (and the gravity waves from GR) moving at the speed of light?
That confuses me since the weak nuclear force only works localy, its signal particle is (unless i'm mixing something here) so heavy that it quickly dissapear. But if it is moving at the speed of light, and time doesn't pass for it, then how can i change?

Yes, i admit i'm not the smartest guy in the block.. Someone care to help me out?

Does the photons "experience" time? If not, how come the weak&strong nuclear forces have a limited area of influence?

Sincerely
Tobias.

Hope i'm not appearing too retarded.

 

[Ziggurat]

From the lights perspective that is.

I'm wondering because as far as GR goes, the closer we get to light speed, the slower time will pass for us.

Time dilation appears in special relativity. You don't need general relativity for it.

There's sort of two answers to that question, and which answer you choose is partly a matter of perspective. One answer is that zero time passes for the light. Another answer is that the question is meaningless to begin with, since the trajectory of a photon is not a valid inertial reference frame (no massive object can adopt that reference frame).

The first answer is perhaps easier to work with, since the math is fairly straight forward. In special relativity, the metric is s^2 = x^2 -(ct)^2, where s^2 measures the distance or time between two points. For space-like separation, s^2 is positive, for time-like separation, s^2 is negative. Along the trajectory of a beam of light, x = ct, so s^2 = 0.

The math behind the second answer comes from the fact that you cannot apply a Lorenz transformation which brings you into (or out of) the "reference frame" of a photon. It's a sort of coordinate singularity.

But..but.. aren't all the signal particles for the weak/strong/EM force (and the gravity waves from GR) moving at the speed of light?

Only massless particles move at c.

That confuses me since the weak nuclear force only works localy, its signal particle is (unless i'm mixing something here) so heavy that it quickly dissapear. But if it is moving at the speed of light, and time doesn't pass for it, then how can i change?

The answer is simply that these massive "signal particles" do not move at c, but are in fact slower.

 

[Grundar]

The photon does not experience time if i recall my physics correctly.

Correct the signal particles for the weak/strong force have mass that is why they don't travel at the speed of light.

Hans

/edit even when i type short messages i'm too slow. better answer above /end edit

 

[TobiasTheViking]

Time dilation appears in special relativity. You don't need general relativity for it.

There's sort of two answers to that question, and which answer you choose is partly a matter of perspective. One answer is that zero time passes for the light. Another answer is that the question is meaningless to begin with, since the trajectory of a photon is not a valid inertial reference frame (no massive object can adopt that reference frame).

The first answer is perhaps easier to work with, since the math is fairly straight forward. In special relativity, the metric is s^2 = x^2 -(ct)^2, where s^2 measures the distance or time between two points. For space-like separation, s^2 is positive, for time-like separation, s^2 is negative. Along the trajectory of a beam of light, x = ct, so s^2 = 0.

The math behind the second answer comes from the fact that you cannot apply a Lorenz transformation which brings you into (or out of) the "reference frame" of a photon. It's a sort of coordinate singularity.



Only massless particles move at c.



The answer is simply that these massive "signal particles" do not move at c, but are in fact slower.

Ah, as randi is so fond of saying. we all make assumptions.. And i made one here

I completely forgot that photons haven't got mass, and i didn't think of that regarding the heavy signal particles for the weak force.

Thanks a bunch for your help,both of you, now i'm a little bit further from being totally incompetent.

 

[David Swidler]

What's it like?