# Energy and Matter and Everything else

1. Aug 21, 2006

### Swapnil

Can everything in the universe be categorized in Energy and Matter??

For examples, velocity, force, electric/magnetic fields, light (maybe) etc would be considered energy. Whereas, chairs, cells, DNA, etc would be considered matter.

2. Aug 21, 2006

### turbo

It depends how you want to categorize things. All matter is energy, and from the E=mc2 relation, you can see that there is a LOT of energy locked up in matter. Our "real world" experiences tell us that condensed matter is different from energy, but fundamentally, they are expressions of one another.

3. Aug 21, 2006

### Swapnil

I see. One more question. Does all matter have mass? I.e If something is massless (eg a photon) then it wouldn't be considered matter, right? (although i admit that, like you pointed out, matter and energy are one in the same thing).

4. Aug 22, 2006

### Swapnil

5. Aug 22, 2006

### WhyIsItSo

I'm not anyone, I'm his cousin no one. Will I do then?

Let's see. (I'm going to get torn up here, I can just feel it *looking over my shoulder to see if Bystander is around*)...

I seem to recall that as the velocity of matter increases, so does its mass. And that matter at velocity C has infinite mass. So:

$$F=ma$$ As $$m\to \infty$$, $$F\to \infty$$

So it takes inifinite energy to accelerate a mass to the speed of light, hence it cannot be done.

Doesn't yet answer your question, I suppose. I wonder that, if ever we could bring a photon to a standstill, would it release infinite energy as it slows down from C?

Embarrassing myself further... Hmmm. No, it would take infinite energy to slow it down too if it had any mass at all.

Ok, what about changing energy to matter. Are we instantaneously converting something at velocity C to stationary matter? Matter has mass, so it can't be accelerated to C, but if we convert it to energy, that energy travels at C.

(I can hear all the physicists out there groaning in pain about now).

Well, I'm going to say that since we can't get anything with mass moving at C, then the term mass is inapplicable to energy.

Therefore, no, a photon has no mass.

Also, energy and mass ARE NOT THE SAME THING. They can be changed from one to the other, and we know that relationship, but that in no way says they are the same. Matter has mass (and thence limits on its velocity), energy does not.

Last edited: Aug 22, 2006
6. Aug 23, 2006

### Farsight

Swapnil: No.

You can't have pure raw energy all on it's own. That's like saying you can have "red" without having something that is red. Energy is a property. Things have energy. Some of these things have mass too. But as to what these things really are I can't say.

7. Jun 19, 2009

### ggb667

Actually that's incorrect.

E=MC^2 - matter and energy are equivalent.

For photons, the energy of a photon is related to it's wavelength (E=hv). More energetic photons are bent more by massive gravitational bodies than are less energetic photons. Photons sufficiently energetic can convert directly into matter via pair production (and vice versa). Photons themselves produce gravity and are both a particle and a wave.

http://en.wikipedia.org/wiki/Kinetic_energy

However that's not the complete story. There is space, which is quite 'real' and it also has energy.

http://en.wikipedia.org/wiki/Vacuum_energy

In addition to space, photons and matter made up of energy in "normal matter" (baryonic matter), there are two other "real things". There appears to be some unknown 'other' type of matter - dark matter that does not interact in with normal matter. We don't really know what that is, but it's possibly composed of massive super symmetric forms of matter with an extremely low interaction cross section. It's the reason the visible edges and centres of galaxies rotate at the same speed. Making this even more complicated is that space itself appears to be expanding at an accelerating rate giving us an even more mysterious thing - 'dark energy'. There may possibly be magnetic monopoles or other relic objects of the big bank (like black holes). As far as matter goes, dense matter can be composed of degenerate matter like neutron stars and quark stars, if you continue to gather mass those objects finally collapse into black holes (which themselves may decay into photons over long time scales).

So, thus far we have space (three apparent spatial dimensions and a single uni-directional time dimension), matter, photons, dark matter and dark energy.

That's all we have good evidence of. Physicists suspect that there may be more dimensions, and that dark matter might interact in those additional dimensions. Also there might be an additional time-like dimension and time itself might just be a low energy approximation of a bi-directional time dimension.

Last edited: Jun 19, 2009