What E=MC^2 means?

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origin":35bda54o said:
Just a point of clarification here - a photon does not have mass. Just because you can define a photon as a particle - for example with the photoelectric effect, that does not mean that the particle has mass. You should look at a photon as a massless particle.

A photon should be considered as information. Only information can travel at light speed, mass or particles can not.

A photon contains the information, that a physical particle changed it's energetic state. Somewhere a electron shifted into higher orbit and sent a photon as a result to inform another physical particle about the change of energetic state.

Without something or somebody to receive and interact with the information, information does not exist. It keeps moving on. If the information is received, it instructs the receiving matter to change it's energetic state.

Mass is not transferred when information is sent or received. Also, sending information costs for the sender (shifting electron into higher atomic orbit requires energy), but the receiver can profit from the same information. Energy was lost somewhere and gained elsewhere. Net energy in the universe remained the same, as per 1st law of thermodynamics suggest.

Energy can not be created or make vanish, but it can be sent elsewhere in the universe using information. A photon is a carrier of that information.


bdewoody":2ad9zm7q said:
Of course it means energy equals mass times the speed of light squared. But I read that one reason we can't go faster than the speed of light is that as an object approaches the speed of light it starts to convert to energy. But the equation says the speed of light squared which is a whole lot bigger number. So are the reasons for the speed limit somewhere else in Einsteins works?

E is energy. Einstein discovered that energy can be exchanged back and forth with matter under the right conditions.

m is mass. Particles with mass can be completely or partially turned into energy (this is the principle behind nuclear power). In the other direction, if there is enough energy available then completely new particles can be created out of “nothing.”

c is the speed of light. Specifically, it is the speed of light through a vacuum (empty space). That speed is 300 million meters/second (3x108 m/s) and is the fastest speed possible in the universe. In this exercise, we’ll investigate how such a speed limit is enforced by nature.

In Einstein’s mass-energy relationship, the factor c2 tells us the conversion factor when mass is converted into energy or vice versa. It’s a lot like the exchange rate for converting one country’s money into another’s. With the conversion factor in this relation, though, you get a whole lot of Joules in exchange for one kilogram! That’s why, even though nuclear power only involves converting a tiny fraction of the fuel mass into energy, it’s such a potentially vast source of energy.

HOWEVER, E=mc2 is not the whole story. It’s true for energy-mass conversions when everything is at rest. We could call mc2 the “mass energy” of a particle at rest. We know that once a particle is moving, it has kinetic energy as well. The theory of relativity includes a more complete formula to give the total energy of a moving particle. For a particle moving at velocity v, the total energy is actually:

Hope this helps.


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