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I know that energy can convert to mass and vice versa.

So are we not looking at simply two forms of the same thing?

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    $\begingroup$ What does it mean for two things to be "two forms of the same thing" in the first place? $\endgroup$ Apr 5 '19 at 15:25
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    $\begingroup$ Is the length of a vector the “same thing” as just one of the components of that vector? Not at all, conceptually! But, numerically, they can be the same if you use a particular coordinate system. You will eventually learn that energy is one of the components of a four-vector (the other three being momentum) and mass is its 4D length. Ignore people who tell you that they are the same thing. BTW, you are free to accept answers that have more downvotes than upvotes, but it tends to indicate that you don’t accept mainstream opinion. $\endgroup$
    – G. Smith
    Apr 5 '19 at 16:43
  • $\begingroup$ But they can convert into one another, right? (I do get the point about the clarity of the statement 'the same thing'... I meant in the sense that water, gas and ice are the same thing but just in a different state) $\endgroup$
    – Stephanie
    Apr 5 '19 at 17:00
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    $\begingroup$ Yes, they can convert into one another under the right circumstances. But this doesn’t change the fact that energy is a four-vector component while mass is a four-vector length and thus are very different kinds of physical quantities. $\endgroup$
    – G. Smith
    Apr 5 '19 at 17:09
  • $\begingroup$ In finance, you can convert stocks and bonds into each other (by selling one and buying the other), but they are completely different kinds of financial investments (owning vs. loaning). No one says that stocks and bonds are the “same thing”. The water/ice/steam analogy is a bad one for mass and energy. This is just a question about of how molecules are arranged in space. $\endgroup$
    – G. Smith
    Apr 5 '19 at 17:15
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Einstein's great realisation (or one of several !) was that energy and mass are the same thing, just (sometimes) measured in different units. There is no conversion involved (unless you mean a conversion of units). The equivalence is made transparent in particle physics where the electronvolt is both a unit of energy and a unit of mass.

"Mass and energy can be seen as two names (and two measurement units) for the same underlying, conserved physical quantity" - Wikipedia Mass-energy equivalence

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  • $\begingroup$ Gandalf and Gareth I have tried to vote positively on your answers but I apparently do not have the authority. Sorry about that. $\endgroup$
    – Stephanie
    Apr 5 '19 at 16:52
  • $\begingroup$ "Electronvolt" - oh YEAH! Fantastic :-) And thanks for the link. Will look into that next... $\endgroup$
    – Stephanie
    Apr 5 '19 at 16:54

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