Category Archives: Relativity

Q: What does “E=mc2” mean?

Physicist: This famous equation is a little more subtle than it appears.  It does provide a relationship between energy and matter, but importantly it does not say that they’re equivalent. First, it’s worth considering what energy actually is.  Rather than … Continue reading

Posted in -- By the Physicist, Equations, Philosophical, Physics, Relativity | 8 Comments

Q: How can the universe expand faster than the speed of light?

Physicist: You’ll often hear that “the universe is expanding faster than the speed of light”.  However, this statement is akin to statements like “green is bigger than happy”.  It’s not even wrong. There are two big things to remember about … Continue reading

Posted in -- By the Physicist, Astronomy, Physics, Relativity | 16 Comments

Q: According to relativity, things get more massive the faster they move. If something were moving fast enough, would it become a black hole?

Physicist: Nopers!  Although that would be an amazingly cool super-weapon. Physics can be pretty complicated, but what makes physics different from lesser sciences, like Calvinball, is that physics has rules that are absolute.  While the consequences can sometimes be difficult … Continue reading

Posted in -- By the Physicist, Physics, Relativity | 8 Comments

Q: How do you prove that the spacetime interval is always the same?

The original question was: Here’s my current dilemma: how does one rigorously prove the invariance of the space-time interval?  In Taylor & Wheeler’s Spacetime Physics, they basically show one very good example of the invariance, then they instruct the reader … Continue reading

Posted in -- By the Physicist, Geometry, Math, Relativity | 5 Comments

Q: Do the past and future exist? If they do, is the future determined and what does that mean for quantum randomness?

Physicist: This is a difficult question to even ask, because the word “exist” carries with it some “time-based assumptions”.  For example, if you ask “does the Colossus of Rhodes exist?” the correct answer should be “it did, but it doesn’t … Continue reading

Posted in -- By the Physicist, Philosophical, Physics, Quantum Theory, Relativity | 34 Comments

Q: If a photon doesn’t experience time, then how can it travel?

Physicist: It’s a little surprising this hasn’t been a post yet. In order to move from one place to another always takes a little time, no matter how fast you’re traveling.  But “time slows down close to the speed of … Continue reading

Posted in -- By the Physicist, Relativity | 70 Comments