# Do we know what energy is ?

1. Sep 8, 2008

### The thinker

Do we know what energy "is"?

Hi everyone,

According to what I have read a string is a minute amount of vibrating energy. Is the word "energy" here used as an approximate for the lay reader?

I was led to this thought because if the vibration of strings make up matter and energy then what's the difference between the "macro energy" produced by vibration and the "pure" non vibrating energy?

Basically I'm asking, what is energy?

Thanks!

2. Sep 8, 2008

### Topher925

Re: Do we know what energy "is"?

Energy is the potential to do work.

3. Sep 9, 2008

### The thinker

Re: Do we know what energy "is"?

That doesn't really answer what energy is though just what it does.

I can't imagine a string of "potential to do work"

4. Sep 9, 2008

### kenewbie

Re: Do we know what energy "is"?

Energy is the sum of a calculation, not a tangible thing.

k

5. Sep 9, 2008

### The thinker

Re: Do we know what energy "is"?

Thats what I used to think, but don't they say that a photon is a packet of energy?

And like I said before how can an intangible thing take the form of a string?

6. Sep 9, 2008

### Staff: Mentor

Re: Do we know what energy "is"?

A photon has energy. It isn't energy itself. Energy is not a "thing". You're looking for a deeper meaning where none is necessary.

7. Sep 9, 2008

### vanesch

Staff Emeritus
Re: Do we know what energy "is"?

It doesn't. All this is figurative talk. As Russ said, you can eventually say that a string HAS energy (or momentum or mass, or whatever other quantifiable property). The only thing that IS energy is a quantity in a calculation.

To give you an analogy: is a bank "interest rate" ?

8. Sep 9, 2008

### Staff: Mentor

Re: Do we know what energy "is"?

Better: Is a bank money?

9. Sep 9, 2008

### vanesch

Staff Emeritus
Re: Do we know what energy "is"?

I was going to say that first, but money also has a tangible representation (paper money, or gold bars, or...), so this was not sufficiently abstract...

10. Sep 9, 2008

### The thinker

Re: Do we know what energy "is"?

hahaha, thats what I used to think until I started reading about string theory and QM which confused me into thinking energy was physical.

So now I have two other questions:

If there is no such thing as pure energy then what is a string?

And what was so revolutionary about E=mc^2 if E is not a real thing?

Thanks again!

11. Sep 9, 2008

### Staff: Mentor

Re: Do we know what energy "is"?

E=mc^2 was revolutionary because no one had connected matter and energy in that way before.

12. Sep 9, 2008

### derek.basler

Re: Do we know what energy "is"?

well when you think about it, energy is primarily mass. Mass is like frozen energy. It really makes you think, what exactly is energy. But when a string vibrates, it gets energy, energy converts into mass.