How far can light go?

[Ganesh Ujwal]

1. When a ray of light is projected, (say) from the surface of Earth to outside in space. The condition is that, there is no obstruction to it till infinity (it travels only in vaccum). My question is that how far can that ray of light go?

2. Also, instead of a ray of light, if I consider a beam of laser with same conditions, then how far can a beam of laser go?

   Compare both the situations.

   And does the light(ray of light and beam of laser) stops after traveling some distance or it has no end?

[iNow]

The challenge here AFAIK is that you are asking a question where the answer needs to be given in terms of the reference frame of light and photons cannot have a valid reference frame since they are by definition never at rest.

[Sensei]

Energy must be conserved, so photon goes until being absorbed by some other particle.

See inverse-square law in context of the Sun.
http://en.wikipedia.org/wiki/Inverse-square_law

 

Sun emits 3.86*10²⁶ J energy per second.
At 1 AMU we're receiving 1367 W/m²
At 1000 AMU we would be receiving 0.001367 W/m²
At 1000000 AMU we would be receiving 1.367*10^-9 W/m²

Go on, and on, and we will reach situation with just one photon per unit of area at some large distance..

 

[ACG52]

But that photon will never stop unless it hits something. The photons making up the CMB have been traveling for over 13 billion years.

[Robittybob1]

But that photon will never stop unless it hits something. The photons making up the CMB have been traveling for over 13 billion years.

Is that traveling towards us for 13 billion years? They have not reflected off anything then came back to us?

Edited December 17, 2014 by Robittybob1

[Delta1212]

Is that traveling towards us for 13 billion years? They have not reflected of anything then came back to us?

That is correct.

[swansont]

Also, instead of a ray of light, if I consider a beam of laser with same conditions, then how far can a beam of laser go?

Compare both the situations.

 

What do you perceive the difference to be?

[Ophiolite]

But that photon will never stop unless it hits something. The photons making up the CMB have been traveling for over 13 billion years.

It must have come as a hell of shock when they ran into something!

[Strange]

And does the light(ray of light and beam of laser) stops after traveling some distance or it has no end?

 

It will never stop (until it is absorbed by some object).

 

I am also curious why you draw a distinction between a ray of light and a laser.

 

The challenge here AFAIK is that you are asking a question where the answer needs to be given in terms of the reference frame of light and photons cannot have a valid reference frame since they are by definition never at rest.

 

Not sure why you think it has to be considered from the frame of reference of the photon (which doesn't exist). You could consider it from our frame of reference (although that gets complicated if you want to take GR and expansion into account). Or the local frame of reference where the photon is passing by.

[iNow]

Was just my interpretation of the OP and something I saw inherent in the question. I stipulate that my interpretation may be different than that of others and is not necessarily correct (hence my inclusion of the AFAIK acronym).

[Strange]

Was just my interpretation of the OP and something I saw inherent in the question. I stipulate that my interpretation may be different than that of others and is not necessarily correct (hence my inclusion of the AFAIK acronym).

 

Sorry, didn't mean to sound as if I was criticising you. Just curious where the idea came from ...

[iNow]

No worries. We're good. Cheers.