Category Archives: — By the Physicist

Q: Why does energy have to be positive (and real)?

The original question was: I was reading an article about tachyons in Wikipedia and stumbled upon this sentence: “Because the total energy must be real then the numerator [mc^2] must also be imaginary”.  I’m confused by the fact that in … Continue reading

Posted in -- By the Physicist, Particle Physics, Physics | 6 Comments

Q: How does the Twin Paradox work?

The original question was: I have a question about the twin paradox.  Is it true that faster aging of the twin who stayed at home happens only when the other twin’s spaceship is accelerating/deceleration (btw, does it matter whether he … Continue reading

Posted in -- By the Physicist, Physics, Relativity | 57 Comments

Q: How can photons have energy and momentum, but no mass?

Physicist: Classically (according to Newton) kinetic energy is given by and momentum is given by , where m is mass and v is velocity.  But if you plug in the mass and velocity for light you get .  But that’s … Continue reading

Posted in -- By the Physicist, Relativity | 227 Comments

Q: If you were on the inside of the Sun falling in, the matter closer to the surface doesn’t affect your acceleration, but the matter closer to the core does. Why is that?

The original question was: Plait talks about the “physics of solid bodies” and why, specifically, if you were on the inside of the Sun falling in, the matter “behind” you- closer to the surface- doesn’t affect your acceleration at all, … Continue reading

Posted in -- By the Physicist, Astronomy, Math, Physics | 14 Comments

Q: How do surge protectors work?

Physicist: To control power in a house or an outlet you’d generally use a fuse.  But fuses are slow, they need time to heat up.  A surge (or the faster “spike”) happen too fast, so reacting to a surge is … Continue reading

Posted in -- By the Physicist, Engineering, Physics | 2 Comments

Relativity and Quantum Mechanics: the elevator pitch

Physicist: A woman on the subway, about two stations away from her stop, asked us “what are relativity and quantum mechanics?” So, this is a two-stop elevator pitch for the two most pivotal sciences since slicedbreadology. Relativity: Speed is just … Continue reading

Posted in -- By the Physicist, Quantum Theory, Relativity | 3 Comments