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Klausnh
2003-May-02, 03:08 AM
Since Einstein proved that energy and mass are equivalent, can we do away with the concept of mass, and instead use only energy? For gravitational attraction (F=Gm1m2/r**2) instead of m1 and m2, could we use E1 and E2, where the energies would include rotational energy. For special relativity, would it be correct too say that an object approaching the c gains energy instead of mass? For GR, would it be correct to say that energy distorts space-time? Photons have no rest mass, so would it make more sense to say that they have no rest energy, ie they are never at rest?

Mainframes
2003-May-02, 10:50 AM
I think it's more along the lines that energy can be converted to mass and vice versa. We have to make some differentiation, just as different types of energies are called different names (kinetic, potential etc.). I suppose you could possibly go as far as saying mass energy, but i think that sounds wierd personally.

Glom
2003-May-02, 12:31 PM
The reason we don't substitute the mass energy relationship into Newton Law of Universal Gravitation is because it is simpler to not do so. Just in the same way we don't calculate the speed of an aeroplane using the Lorentz factor. On this scale, we don't need to complicate things by including factors too small to be significant.

Eta C
2003-May-02, 01:00 PM
In nuclear and particle physics we do use energy as the unit of mass. The usual unit is the electron-Volt (eV), the energy an electron picks up as it passes through a potential difference of 1 Volt. You then move on to thousand electron Volts (keV), million (MeV) and billion (GeV) (that's the American billion by the way, not the British ). So, for example, the electron has a mass of 511 keV, the proton 938 MeV. The most recent measurements of the neutrino mass are on the order of 10 eV. compared to the next heaviest particle, the electron, it is essentially massless.

Of course, technically the unit should be MeV/c^2. Being lazy, however, physicists usually drop the c as understood and just quote the energy value as the mass.

Klausnh
2003-May-04, 02:06 AM
How much simpler can the Universe be? It consists only of space-time and energy. :) Maybe some day another Einstein will come along and show that space-time and energy are equivalent and the universe will be just space-time.

Zamboni
2003-May-04, 06:05 PM
How much simpler can the Universe be? It consists only of space-time and energy. :) Maybe some day another Einstein will come along and show that space-time and energy are equivalent and the universe will be just space-time.

Whatever happend to dimensions? (eg. Kaluza-klein)
I thought they're still trying to unify the four forces...?