# E=mc2 ??

Energy can not be created nor destroyed…Einstein said that energy can become matter and matter can become energy…but the sum total of energy + matter is always equal. Right?

Could some one explain what else this equation means but like in simple terms?

It means that a small amount of matter can be converted into a large amount of energy (Nuclear fission/fusion). Or that a large amount of energy can be used to create a small amount of matter.
See this Cite

What unit is “c” in? Miles?

Doesn’t matter (no pun intended:cool: ). If c is in miles per hour and m is in kilograms, then E will be in kilogram-miles per hour. The units used on one side of the equation will determine the units to use on the other side.

Doesn’t matter (no pun intended:cool: ). If c is in miles per hour and m is in kilograms, then E will be in kilogram-miles squared per hour squared. The units used on one side of the equation will determine the units to use on the other side.

Darn, wasn’t quick enuff to stop my first, stupider, post

Er, I’ve had this explained to me before, but what is an “hour squared”?

Also… what is a kilogram-mile?

Thats what I dont understand… If it takes a small amount of matter to make alot of energy then how can they always be equal in the universe? Or did I get that part wrong?

Im so totally confused…

I’ll check that site out…thax.

Umm… well, an hour sqaured is an hour times an hour. And a kilogram mile is a kilogram times a mile. shrugs Nothing too it, really. But also not very intuitively useful units.

I think you’re confused.

E=MC[sup]2[/sup] just means matter and energy can be converted back and forth into each other.

It seems like you are assuming all the matter in the Universe is equal to all the energy in the Universe. That doesn’t make sense because matter and energy are equivalent…matter=energy=matter=energy…just different forms of the same thing (like liquid water versus ice water…both still water).

A sample of many.

Whack is correct. When you are studying Einstein’s equations, it’s helpful to think of matter and energy as two aspects of the same thing, commonly called mass-energy. The amount of mass-energy in the Universe is a constant, no matter what percentage of it exhibits which set of properties at the moment.

E=mc[sup]2[/sup] is like all physical equations: dimensionless. The dimensions used on one side determine the dimensions derived for the other side.

Distance per time squared means distance per time per time. It’s a rate of acceleration. For example, g is 9.8 meters per second squared. That means every second, something falling on Earth (and exhibiting the acceleration defined by g) gets 9.8 meters per second faster.

0 s == 0 m/s
1 s == 9.8 m/s
2 s == 19.6 m/s
3 s == 29.4 m/s
etc.

One more.

Oh, and one more thing. Mass and energy are not the same thing. In special relativity there’s a thing called the energy momentum four vector which in some respects is as basic as you can get. In any case, energy is the time component of the four vector, momentum is the space component and mass is the magnitude of the four vector. This is all summed up in the equation:

E[sup]2[/sup] = m[sup]2[/sup]c[sup]4[/sup] + p[sup]2[/sup]c[sup]2[/sup]

E = energy
m = mass
p = momentum
c does not equal 1

Despite your further explanation you lost me. Just when you think you get a handle on something leave it to a physicist to screw it up for you .

I’m really hoping we’re getting caught on semantics here.

Stop me if this analogy is inappropriate: Liquid water and Frozen water are not the same thing but they are different forms of the same thing…water.

VERY loosely speaking I thought energy and matter worked the same way. From your own quote of yourself if you explode a nuclear device in a vault and convert mass to energy (or vice versa) from outside the vault all measurements will be the same. Less matter, more energy…doesn’t matter. Just as if I melted my ice to a liquid then turned the liquid into a gas…I still have the same amount of water and have merely changed its aspect.

What have I missed that doesn’t require 8 years post grad work to understand?

From Ring:

Whoa! How did you write the exponent? I was answering a math question and had to use carrots.

Now I see from my post that it doesn’t work for me even when I quote!

To get really strange, the new quantum theories hypothesize that at the sub-atomic level energy and matter are made up of the same stuff. For instance, in string theory, one of the more popular quantum explanations, the very smallest unit of anything is the string (hence the name) which can be visualized as a rubber-band with a certain number of whole waves in it. The number of waves, or the frequency of the band determines whether you get photon, graviton, proton boson, muon etc . . .

This is of course a VERY simplified explanation. For more in depth info in terms even I could understand I would recommend:

[ul]
[li]The Dancing Wu Li Masters[/li][li]In Search of Schroedingers Cat[/li][/ul]

They’re called carets. ^ is a caret. Note spelling.

Try the [sup] tag. Type x[sup]2[/sup] to get the desired effect.

The [sub] tag does the right thing, too.

I think a lot of people get hung up on this because they think mass and energy are things. But they’re not things – they’re properties of a system. This is not to say they’re not intimately related, they are. If you study the equation:

m[sup]2[/sup] = E[sup]2[/sup] - p[sup]2[/sup]

You can see that if the momentum is zero the mass of the system equals the energy of the system, or to put it another way – mass is equal to the energy of the system that cannot be transformed away.

If you wanted to, you could abandon the concept of mass altogether and just talk about the magnitude of the energy momentum four-vector, but the concept of mass is so ingrained that I doubt this will ever happen.