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17 votes
6 answers
7k views

How can a grain of sand be "spaghettified" when nearing a black hole?

I have a hard time wrapping my head around this "spaghettification" process that apparently takes places when getting close to a black hole. Gravity is proportional to the distance of the ...
d-b's user avatar
  • 439
1 vote
2 answers
128 views

Is $\frac{dE}{dt}=0$ in an accelerating particle’s instantaneous rest frame?

My special relativity book uses an argument that involves $\frac{dE}{dt}=0$ in an accelerating particles rest frame (to show a force parallel to a particles velocity is parallel in all frames). ...
Alex Gower's user avatar
  • 2,604
1 vote
0 answers
62 views

Lagrangian of free particle relativistic case

Why must the covariant Lagrangian of a free particle be a first-order differential?
oscar cepeda giraldo's user avatar