# Can matter be defined strictly in terms of mass and energy?

1. Jun 14, 2013

### la6ki

I was reading some articles and discussions on the topic and got confused when I read that conventionally photons and all other massless particles aren't considered a form of matter. The Wiki article on matter begins with the statement that the term itself is poorly defined.

I was thinking that a good way to define the term could be to say that matter is something which has mass or energy. This would also capture our intuitive understanding of the concept of material substance, since when dualists speak of the "non-material world", they certainly don't have photons in mind.

If energy can be converted to matter and matter to energy, and only the sum is concerved, why aren't massless particles considered material?

2. Jun 14, 2013

### StarsRuler

Matter is all that has a position in space and has mass. Non massive particles like photons aren´t matter. There is no ambiguity. There is a definition present in innumerable sources, I don´t know the Wikipedia article where consider non massive particles matter but it is completely erroneous. The convenious is absolute.

3. Jun 14, 2013

### la6ki

The Wikipedia article doesn't consider non-massive particles matter, on the contrary. I'm aware of the conventional definition but the reason I started this thread is to question it. Why not include particles which have energy in it? It seems much more natural to do so, as I gave an argument in the OP.

4. Jun 14, 2013

### phinds

Well, it may seem more natural to you, but do you really think you are going to get the physics community to change terminology to suit you?

5. Jun 14, 2013

### ZapperZ

Staff Emeritus
This is as meaningful as the argument on whether Pluto is a planet or not. If all you care about is the semantics, then this is no longer physics.

You can call it anything you like. The question that should matter is, what is the physics involved? Does calling massless particle "matter" change anything? Is this such an important question that it is published in Physical Review Letters? As far as I can tell, you haven't made any physics argument. Saying that matter can be converted into energy, etc. is not a justification. Would you say that your $1 bill is food, since it can be converted into a bag of potato chips? Zz. 6. Jun 14, 2013 ### Grombely ?? People may define matter as they wish, it seems . Photons have Mass and Energy . So do electrons and quarks for that matter- I've always considered this stuff matter. Also ZapperZ; you don't turn$1 directly into food..

7. Jun 14, 2013

### ZapperZ

Staff Emeritus
You also do not turn photons into mass "directly". Pair production, for example, requires an exchange of momentum with a massive particle. That's why we often shot gamma photons into crystals with large atomic mass. So there are other external factors involved here.

BTW, photons do not has "mass". Read our Relativity FAQ and also the numerous threads we already have on this topic.

Zz.