# Ask a Physicist

- What is energy?
- What is mass?
- What is matter?
- Where did total gravitational energy of the universe come from? - by Alan Guth (from Appendix A of his book The Inflationary Universe)

- Does E = mc
^{2}mean that mass can be conveted into energy? - Does E = mc
^{2}mean that matter can be conveted into energy? - Is Newton's 1st Law written as F = ma or F = dp/dt?
- Is a photon "energy"?
- Are mass and energy the same thing?
- Is mass "congealed" or "frozen" energy?

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