Recent content by Karl Coryat

I think you mean no, because those numbers reflect twice the Newtonian prediction (19.6 m/s2). I think what you're telling me is, if we had instruments of arbitrary precision, in the limit of spacetime being locally flat, we would measure light to "fall" at the Newtonian rate; but if we zoomed...

I appreciate the explanations! Let me rephrase that last question as, Does a light beam parallel to the Earth's surface deflect downward at 1.96 x 10–9 meters vertically for every 9 kilometers horizontally? (It's a conceptual question rather than a practical one.)

The Eddington Experiment famously confirmed GR by showing, as Einstein had predicted, a deflection of starlight by the Sun that was double the deflection expected by Newtonian gravity. I don't understand where Einstein's 2x number came from. I make the following assumptions: 1. That a ray of...

Yes, that clears up some things. Thank you. I'd still like to explain how tidal forces arise near a black hole without appealing to Newtonian forces of gravity pulling an object apart. Do you know a good online resource for that?

I assumed that a reference frame cannot span two locations with different spacetime curvatures. For example, I have seen it said multiple times that no reference frame can span the entire earth. So I assumed the same principle applies here.

I enjoy explaining spacetime curvature to people with a rank-beginner understanding of GR. But someone asked about that favorite concept in pop-sci, spaghettification. I'm having a hard time with it. If you fell into a black hole, there's no reference frame within which you could describe...

Fascinating, thank you!

Thank you.

So the error is in assuming that if we're in flat spacetime, that we can make measurements of an object in curved spacetime that are consistent with GR?

Super-basic question that I'm embarrassed to ask. It's just what the summary says: Taking Earth's center of mass as our reference frame, how does GR account for an inertial object near the surface approaching with an acceleration of G? I assume (perhaps incorrectly) that this is an inertial...

I realize that nothing causes an excited atom to emit a photon, and that it's a random process. But someone was asking me about why energized systems in general tend to lose their energy to the environment and move toward equilibrium. I mentioned that an inflated balloon, given a hole, will tend...

The point of the thread was to ask if an accelerometer that had been treated in a certain way, under certain conditions, would mimic an ordinary accelerometer's null result in freefall. If you really want to know, I've been battling relativity deniers who don't like the proposition that an...

I never said I did.

Yeah. I realize it's a contrived boundary condition. I'm just asking if my assumptions are correct regarding what this system would physically do in these two situations (free to accelerate and stopped from accelerating), and if perhaps I'm overlooking something, as I often do.

Fair enough. Let me try to strip it down as much as I can. We'll model our accelerometer as a 1kg mass with three 1g masses attached by springs. In deep space we’ll charge all of the masses, and the springs, uniformly (it's all the same material with uniform charge density). Now we bring the...