# $E=mc^2$: Why does the speed of light constant affect the Energy or Mass of an object? [closed]

So this is really just for fun. I often talk to my friend who studied some Physics degree (or similar) and he simply cannot accept the possibility it could be wrong in any way. To the point where he gets angry if I try to challenge it.

but if E=mc2, to me this implies that the speed of light itself is somehow controlling the amount of matter an object has. It seems mindboggling to me that it's a coincidence in nature, like what does the speed of light have to do with massive something is.

Also , is it 100% proven that in ALL circumstances/scenarios mass and energy values are directly linked, or have there been exceptions.

Finally (and off topic) that double slit test seems to me as prove that we don't understand even electrons behaviour fully (the conclusion that it will behave differently when it is being observed to when not observed doesn't sit well with me LOL!)

I'd love to hear any facts, opinions or discussion here. And of course would love to learn more and understand why this formula (and in fact the double slit thing) is so widely accepted by all experts.

• I am voting to close this question because it is not well focused, and it shows little prior research into what the equation $E=mc^2$ actually means. – BioPhysicist Dec 24 '18 at 14:28
• fair play, this was basically just for fun and to hear reasons from experts. No bother, I can delete it if you'd lke – Big T Larrity Dec 24 '18 at 14:30
• I didn't say you should delete it, and I am glad your are trying to learn more about physics and having fun doing it. I'm just one vote. Others might disagree. You might get a good answer. You could edit the question to focus on a single question. A close vote doesn't mean it should be deleted right now. I was just giving my reason for voting to close as the question stands right now. – BioPhysicist Dec 24 '18 at 14:35
• None of the answers have addressed your question about exceptions to $E=mc^2$. None have ever been observed. Any exception would be Nobel Prize stuff. Testing of this formula takes place on a daily basis in particle accelerators, which create new particles with mass out of energy, or annihiliate particles with mass into energy. And of course this formula is behind the destructive power of fission and fusion bombs. – G. Smith Dec 24 '18 at 17:20
• very good point G Smith, but I found Kyles answer very interesting with the links etc. I didn't really ask an 'answerable' question. It was more something I wanted to learn about but whenever I ask people IRL they seem to get mad if you challenge something they cant explain. It just seems like a huge coincidence that the c^2 has anything to do with the equation of calculating somethings mass (to my slow brain lol, I mean light has no mass AFAIK ). But very honestly , I havent done any research at all, and I don;t understand much of it when I do try research it. No harm done tho :] – Big T Larrity Dec 24 '18 at 17:28

The constant $$c$$ is largely arbitrary, mostly due to human definitions of things like the meter and the second (though we defined the speed of light to be an exact value in the 1980s, and the meter & second are now derived from it). In many cases, physicists use units in which $$c=1$$, so then you have that $$E=m$$ which should indicate that $$c$$ isn't controlling anything here, it's really just a value used to convert a mass-quantity into an energy-quantity.

You may want to look at other related questions and answers on the subject:

And probably many others.

• many thanks for this information. I have trouble understanding the c=1 part but that is due to my lack of understanding for the topic in general. Thanks for the helpful answers and further reading. (The writer of that first links question has put into words better than me, exactly what I was trying to ask in the first place) – Big T Larrity Dec 24 '18 at 16:37
• try c equals 1 foot per nanosecond (pretty close to) – user45664 Dec 24 '18 at 20:28
• Nice links, but none of them really address why the conversion factor is $c^2$. – PM 2Ring Dec 24 '18 at 22:22
• @PM2Ring that's because it wasn't my intent to explain that, I only wanted to point out that $c$ doesn't "control" anything that OP seemed to think it does. – Kyle Kanos Dec 25 '18 at 16:27

When dealing with anything to do with the speed of light, I find it helpful to think of c not as a speed, but as a universal speed limit. So you can think of e=mc^2 because e=m(c+1)^2 is just impossible. C is just the highest number possible in the world of speed and therefore energy. It's just a way of thinking, but I hope it helps the understanding.

• The question is why $c$ seemingly affects the energy or mass of something, not why it is a universal speed limit. – Kyle Kanos Dec 24 '18 at 15:58
• @KyleKanos What I was trying to get across that c is the maximum possible number. I took the OP as "why c and not some other number?" The reason is that it is the maximum possible amount. If c was a higher number, then the amount of energy in a mass would continue to rise until it reached that new, higher number. Like I said earlier, it's more a way of thinking than anything else. – foolishmuse Dec 24 '18 at 19:52

I like your question, you are taking from a different point of view. The equation is just a mathematical consequence of the postulates of Special Relativity, you can find it’s derivation in University Physics by Young. Actually the same result was found by Dirac through the postulates of Quantum Mechanics and again it was a mathematical consequence but he got a plus and minus sign in his equation. Your thinking is very keen and sharp but not needed in physics, Physics is about being humble to it and it’s laws. Hope it helps

• I fail to see how this answers the question. If anything, it should be left as a comment (which requires 50 rep). – Kyle Kanos Dec 24 '18 at 16:50
• @KyleKanos Oh now I see, people on this site look for reputation not the information. Thank you for that. – user214211 Dec 24 '18 at 16:53
• not sure I follow how that understanding comes about. People use this site to gain and share understanding of physics through asking and answering questions. Certain aspects of participation, however, does require reputation. Your post doesn't seem to answer the question, it's side commentary about how good it is to an questions and investigate things, rather than answering what role $c$ plays in the mass-energy relation. – Kyle Kanos Dec 24 '18 at 16:55
• OP’s aim was to know how that c came over there and how it governs the law. I said it came over there due to mathematics. Not by nature. – user214211 Dec 24 '18 at 17:02
• Not sure how that follows from the title and the statement this implies that the speed of light itself is somehow controlling the amount of matter an object has – Kyle Kanos Dec 24 '18 at 17:05

I like the E =mc^2 part of the question because I asked this in my school and my teacher was extremely pleased with me. So I will now try to answer the question.

Honestly though the double slit experiment has nothing to with it. Everyone should have a look at the single electron diffraction video. For example https://youtu.be/jvO0P5-SMxk. And I mean EVERYONE. The electron has simply a probability for falling at any point on the screen. Initially there are a few random pounts but as the numbers increase the inteference becomes obvious. There is no doubt whatsoever. Why nature behaves in this absurd ( to human minds) way is simply unknown. But it does and like Feynman I am delighted with it.

Now for the E=mc^2 issue. The speed of light is " not controlling the amount of matter an object has ". That formula determines how much energy is created when a mass m is converted into energy. This for example is happening in the sun. Once again experiments confirm it with no scope for any doubt

The formula itself emerges because Einstein asked a question. Light propagates as a wave. But Maxwell's equations don't change if the source is moving. So the velocity shouldn't change with the velocity of the source. This was subsequently directly verified. One of the consequences of this is the formula.

And before you ask, this is true in quantum mechanics too. But it becomes necessary to do a lot of maths.

NOTE FOR SERIOUS PHYSICISTS. I found through experience that this approach works better when explaining to non physicists rather than start a mathematical derivation from Michelson Morley experiment.

I have written a monograph "experimenting with the quantum world" published by vigyan prasar for such an audience. It can be down loaded from archives.org

• $E=mc^2$ doesn't 'determine how much energy is created when a mass m is converted into energy', it states the mass of a system of energy $E$, or the energy of a system of mass $m$. Minutephysics did a nice video on it youtu.be/hW7DW9NIO9M – Phineas Nicolson Dec 27 '18 at 12:33