"There is no energy in matter except that absorbed from the medium."

What does he mean by this?

Einstein's famous equation $E=mc^2$ shows equivalence between mass and energy. Does this equation only mean that energy has mass? My initial understanding would be that matter can be converted into energy. However, if Tesla is right, then that cannot be since there is no energy in matter, only stored energy.

Can someone clarify my confusion?

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    $\begingroup$ This would be an excellent question for history of science and mathematics - I'd like to see an answer. However, Tesla's scientific thoughts were formed long before Einstein formed his and his view of matter and energy would have been profoundly different from that which we have now. So, I don't think you'll get an answer to this here, but rather from someone with a better knowledge of Tesla's life and / or detailed knowledge of 19th century physics. $\endgroup$ Commented Jun 9, 2015 at 12:42
  • $\begingroup$ During Tesla's time, Energy and Mass were two different concepts altogether. To them, matter are things that have mass, and they can posses energy by moving or by being in a potential forcefield. On its own however, it has no energy. Now however, mass or more specifically rest mass, has energy which leads to the equation above. Also regarding your statement "Energy has mass", you are wrong. Mass is energy but energy may not always have mass. For example a photon or any massless particles. $\endgroup$
    – Horus
    Commented Jun 9, 2015 at 15:05
  • $\begingroup$ @Horus, can't any energy be converted to mass and any mass likewise converted to energy? $\endgroup$
    – ouflak
    Commented Jun 10, 2015 at 12:44
  • $\begingroup$ @ouflak: Tesla wrote that in 1932. According to Wikipedia, the discovery of nuclear fission occurred in 1938. Top physicists probably understood that it was theoretically possible, but you cannot assume it was mainstream knowledge. $\endgroup$ Commented Jun 10, 2015 at 17:29
  • $\begingroup$ @ouflak Yes energy can be converted to mass and vice versa. I was just remarking how just because something has energy, does not automatically mean it has mass. $\endgroup$
    – Horus
    Commented Jun 19, 2015 at 10:02

2 Answers 2


You've taken this out of context.

The context in which Tesla is writing, he's talking about kinetic energy and heat. Just a few sentences previously he states:

...according to an experimental findings and deductions of positive science, any material substance (cooled down to the absolute zero of temperature) should be devoid of an internal movement and energy, so to speak, dead.

In that context, he's not denying mass-energy equivalence. The only thing he is mistaken about is not accounting for the quantum mechanical zero-point energy (seems forgivable to not be that pedantic in his writing).

While he may have disagreed with Einstein's work, it's not clear at all that he's denying it with that single statement.

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    $\begingroup$ I really didn't think to google the phrase (which I presume is how you found the great link +1): I just thought Tesla's conception of these things would be so vastly different from ours that I doubted I'd understand anything I found written by him. But not so. $\endgroup$ Commented Jun 10, 2015 at 8:45

I think that sentence shows that Tesla did not quite grasp the results from relativity. This is not unusual, as many physicists required many years to fully accept relativity, but by 1932 (the date of the writing of that text) I would expect it to be already orthodox knowledge.

In any case, Tesla is known to have been a self-taught experimental genius and it's not unreasonable to believe his understanding of fundamental physics was flawed. This does not overshadow his achievements and genius, it just means his talent was not regarding the same inquiries as for, say, Einstein or other theoretical physics.

The best understanding of Einstein's relation is that Energy and Mass can be seen as two sides of the same coin: mass can be converted to energy and energy to mass. Examples:

  1. Creation of particles at accelerators: energy to mass.
  2. Annihilation of matter (with anti-matter): mass to energy.
  3. Mass of nucleons is not the sum of the mass of the (valence) quarks, instead it is the related to the energy of the strong nuclear force confinement.

So Tesla was not right about his interpretation, but then again you have to remember that Tesla was an experimental, engineering, inventor genius and not a theoretical physicist. In fact, he had no formal training as a physicist (not a fully formed field at the time) and only partial higher training in scientific and engineering areas.

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    $\begingroup$ I have one objection to this, but it is a significant one: $E=mc^2$ says nothing about converting energy to mass or vice versa. If you do find some way to do the conversion, it tells you how much energy corresponds to a given amount of mass. $\endgroup$
    – David Z
    Commented Jun 10, 2015 at 8:37
  • $\begingroup$ @DavidZ I believe what is meant by "conversion" here is a conversion of terms. The equation expresses the proportionality of mass to energy. Within physics, one would use the equivalent energy of a mass within any number of calculations. The value of the equivalent energy is derived by "converting" the mass term to energy. It is misleading and that nuance really should be pointed out. E = mc^2 doesn't mean that all mass can freely be converted to energy, ad-hoc. Whether mass can be converted in such a manner is not relevant to what the equation is describing. $\endgroup$ Commented Aug 23, 2023 at 2:56

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