# Massless Particles.

1. Jan 15, 2008

### _Mayday_

Hey, well I've just been having a discussion with someone this minute, about travelling at the speed of light. We said that for something to travel at the speed of light, the partcile will need to be massless, but when I looked it up, I found that a particle has to have mass? Does a photon have a mass? It can be made to go faster than the speed of light? How does that work? I mean, how can something with mass, travel faster than the speed of light?

2. Jan 15, 2008

### ranger

Last edited by a moderator: May 3, 2017
3. Jan 15, 2008

### _Mayday_

I've always thought, that there is no such thing as a massless particle? Special relativity gives a photon no mass, I dont understand that is that like an exception or something?

AND I've read a photon can travel faster than the speed of light, but yet has a mass?

4. Jan 15, 2008

### D H

Staff Emeritus

The speed of light in a medium (e.g., glass) is less than the speed of light in a vacuum. Photons, which are indeed massless, cannot travel faster than speed of light, period. Massive particles traveling near the speed of light can briefly exceed the speed of light in when the enter some medium, in which case they emit http://en.wikipedia.org/wiki/Cherenkov_radiation" [Broken].

Last edited by a moderator: May 3, 2017
5. Jan 15, 2008

### _Mayday_

^ I have read the first link, but I am really struggling to understand it? Can anyone explain it more simply?

"Photons are traditionally said to be massless."

I'm really struggling to understand what it is saying? Sorry, it just doesn't make sense to me? Some places say yes and some say no? Or is it not taking its mass into account as it is negligable?

I don't want it to come across as if I haven't read through it, I have a few times it's just not making sense to me =/ cheers for the help so far =]

6. Jan 15, 2008

### Staff: Mentor

7. Jan 15, 2008

### _Mayday_

Well, as I've said above, I am not sure if a photon has mass yet, because I've always been taught that there is no such thing as a massless object.

I am really struggling to get to grasps with this, the links proved very difficult to understand.

I just really want to know what I posted in my first post, could anyone explain it to me?

8. Jan 15, 2008

### ZapperZ

Staff Emeritus
Which part of "Photons are traditionally said to be massless" did you not understand?

You should also read the Physics Forums FAQ in this subforum.

Zz.

9. Jan 15, 2008

### _Mayday_

^ It's just clicked, thank you so much guys/gals my knowledge of this area of physics is very near to 0 so things take a while to make sense but thank you so much, now atleast I can contribute towards a discussion on such matters, even if it is still limited.