Recent content by meekerdb

No. But in a sense energy-density has a shape in general relativity. The stress-energy density at a point is a 2nd rank tensor, which can be thought of as an ellipsoid in stress-energy space.

First thing to notice is that force and acceleration are vectors, mass is a scalar. So the multiplication is in vector space. Multiplying a vector by a scalar is quite different from multiplying two vectors which may be a dot product or a cross product. But you can't add things with different...

In relativity thought experiments the clocks are always ideal clocks that run at exactly the same rate as could be confirmed by putting them side by side. The relativistic effects called "time dilation" are not affects on the clocks; they are due to moving the clocks along different paths in...

Same answer. Power increases because you're calculating it relative to an increasing velocity. Total energy and momentum are conserved, including the exhaust and chemical energy.

The easy solution is to equate energies: 1/2 mv^2 = Pt so v = sqrt[2Pt/m].

It's because you have posed the problem in terms of constant power, where power is a relative value, because kinetic energy is a relative value. If the car had a rocket engine it could have constant thrust and acceleration which are absolute values.

I agree with the explanations by David Lewis and gleem. But I think they missed a point that acceleration is not only dimensionally different, it's also a vector, and so is F. So F=(m1+m2)a makes sense but F=m(a1+a2) doesn't. I also noticed that no one suggested a book on this subject. There...

If it's real how do you explain that the same result can be obtained by Feynmann's path integral method?

Pushed to it's limit, neither the light nor the electron is ontic. They are all "things" we merely theorize from our perceptions. At one time there were different theories explaining those same perceptions, e.g. when the Greeks thought of vision as rays that reached out from one's eye. This...

Almost everything we think we know about a black hole is from solutions of Einstein's equations. We have every reason to believe this well tested theory except in the neighborhood of where it predicts singularities. So the existence of an event horizon and the appearance to a distant observer...

Ok, now consider the limit in which one black hole is much smaller than the other. It's never "stuck" on the event horizon, but how is it different from some other extended bit of mass-energy falling in? You say there is only one event horizon, but it must change and it's change can only...

Is the increase in the size of the black hole observable at a great distance in a finite time? If so, I'd say that's an observation that the object has crossed the event horizon...although of course one can never "see" that.

If it's true that a distant observer never "sees" an object reach the event horizon of a black hole, then what do you make of LIGO's observation of one black hole falling into another and the observed merger being complete in a minute. It certainly makes no sense for one black hole to be seen...

It's so A can be in almost flat spacetime.

There's a problem with things like "same acceleration profile" and "same relative velocity" and "rigid acceleration". They are not mutually consistent. The front an back of a ship that accelerates, change relative velocity because time dilation is different at the front and back. "Rigid...