is E = mc^2 even correct?

[ShawnD1]

As you have all probably learned in school, kinetic energy of a something is E = (1/2)mv^2. We can determine the energy of a photon of light with the equation E = hf where h is planck's constant and f is the frenquency. we know that the velocity of light is 3x10^8 so then we can solve for the mass of a photon of light..... but wait a second, in school we always used to use Einstein's formula E = mc^2 where c is the velocity of light.

Common sense would say to use the kinetic energy formula to solve for the mass of light but we are always told to use einstein's formula. Why is that? If you put the formulas together, something just doesn't quite add up.
(1/2)mv^2 = mv^2
1/2 = 1???

Is there any proof that Einstein's formula works? If so, what is it?

The expression E = mc^2 is the rest energy of an object of rest mass m. In motion, the object's total energy is a sum of its rest energy and its kinetic energy. That is:

E = [(p^2c^2) + m^2c^4]^(1/2)

where p is the object's momentum. You get this more general equation for energy using the momentum-energy 4-vector. The 4 vector contains four components: three spatial components of momentum and one time component of momentum. E is just the magnitude of this vector. If you square both sides of the equation, you get:

E2 = (p^2c^2) + (m^2c^4).

Notice that you get E^2 = m^2c^4 if the object has zero momentum; that is, if the object is at rest, thus arriving at E=mc^2.

Both concepts you present are considered outdated among many circles. I recommend taking a look at the documentation for Millennium Relativity. Many mathematical models presented show how several new age theorists can directly correlate relativity to kinetic energy.

http://www.mrelativity.net/

And finally, mathematically, Einstein's formula can be proven quite easily.

http://www.math.iupui.edu/m163/matlab/Honors/HP13.pdf

Robert Richmond

[Siliconjunkie]

But what about the spatial gravity of the photon beam when refracted by a knuder mirror?

[ShawnD1]

E = [(p^2c^2) + m^2c^4]^(1/2)

That looks like pythagorus' thing. Why is the energy the square root of the sum of the squares? Why not just an addition of the two?

Correlates to kinetic energy being directly proportional to velocity, not mass, as defined by quantum mechanics. The scope of Einstien's "special relativity" theory (the formula I introduced above) is likely well beyond either of ours' current Mathematical experience.

Robert Richmond

Since this is a tech help site, how about we use the appropriate symbols here:

E=mc˛

[Just paste the ˛ from character map, or use ALT + 0178. ]

Just trying to be helpful, even if I don't have a clue what's going on!

Cheers
Mick

[thekingofpain]

Common sense would say to use the kinetic energy formula to solve for the mass of light but we are always told to use einstein's formula.

I know this wont assist---

But that aint so common---yer makin me feel double dopey, like I shoulda learned this at some point in all those years---(probably did but didnt retain it)

---Good thing Roberts here---
:-)

[ShawnD1]

King, did you take physics in school? They usualy teach energy in grades 11 and 12. Light and photons is introduced in grade 12 but not really explained much. What i know about light and waves is a mix of school, reading technical papers on the internet and watching discovery channel.

Rob, I only don't understand what they are doing because they don't explain what they are doing in that paper. It say things like "well we'll take our mass then do this with it then do that". I can follow the math parts but I don't follow why they are doing it.

[thekingofpain]

Physics? in the 60's/70's?---yer kiddin---most of the kids I went to school with couldnt even spell it...

We are in contrast then, as I often work better with the text analysis instead of straight mathematical documenation.

Perhaps a visual model will offer a better explanation:

http://www.drphysics.com/syllabus/energy/energy.html

I also believe this link will prove quite helpful in addressing your original question.

http://www.btinternet.com/~j.doyle/SR/Emc2/Derive.htm

Robert Richmond