Assuming that c is a "conversion factor" to convert between space and time,(adsbygoogle = window.adsbygoogle || []).push({});

Then, in 4-vector, we have x_1 through x_3, and t, where, x/c = t

x/c = t, (where t = time, c= lightspeed, x = spacial dimension)

If we do what we did to space to get time, to momentum,

p/c = m*v/c = m (x/t) / c = m(x/c)/t = mt/t = m

we actually end up with mass... not energy...

So, there is an inconsistency, and I must have made a mistake somewhere. Can you please describe the method and mathematical proof and context for calling energy the component of momentum that is in the time dimension?

Thank you very much. -- j

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# In 4-momentum, why is E the 4th component?

**Physics Forums | Science Articles, Homework Help, Discussion**