Recent content by Bandersnatch

These are excellent analyses. I'm wondering about applications to astronomy.

If our star produced such a deep gravity well that time dilation were significant, then you'd see all velocities speed up, at all galactic radii - instead, the inner velocities are just about right, while the outer are too high. If the argument were to use the differences in the depth of the...

I suppose the significance could manifest when you're in a spaceship and Houston tells you to rotate the craft for a retrograde burn. It might be nice to know what they're talking about. And in any case, it's the context the OP asked about.

You're thinking of 'apparent retrograde motion', on the celestial sphere. Where this thread talks about retrograde, it's in the context of directions of orbits. A different thing.

I'm not sure why you're framing this as an objection. Yes, that's what you do, and that's what makes it unambiguous. Wasn't the perceived ambiguity in picking the reference 'north' direction from which to judge the rotation the point you initially took issue with? We may be talking at cross...

Why wouldn't it be? The direction of the pseudovector in whatever reference frame we pick provides all the information about the direction of the rotation, and one is still free to describe rotation of bodies in relative terms using words like clockwise/anticlockwise. The point is to remove...

Yet, the right-hand rule provides an unambiguous direction towards the rotational north pole. This isn't as much of a problem as you make it out to be.

As has been said, you can't get a velocity out of the Hubble constant, because its dimension is that of a frequency. I can appreciate that it's not very helpful as far as making it relatable, though. But maybe this will be - since H0 is stated as some speed per some distance, it tells you how...

I feel like I should maybe be more constructive with my comments. Do you need the apocalypse to be caused by the tides? I understand that the visual of a foreign astrophysical body looming over the sky as the world ends is the selling factor here, but maybe we can work out some alternatives. I...

Look, with some rounding of the numbers, at 200 km/s the body is covering 0.1 AU in a day. So to trigger an earthquake a day before perigee you need a body that is sufficiently massive at the aforementioned distance to have significantly higher tidal influence than the Moon, which is some 40...

I don't think that's possible. It'd have to be another star passing by, and a sizeable one too. In which case earthquakes would be the least of your protagonist's problems.

At 200km/s and 3600 seconds in an hour, the planet traverses the entire diameter of the lunar orbit in one hour. If it's a small body, having to pass close-by for the desired tidal effects, then you're looking at minutes of earthquakes at most.

So, back of an envelope, that's approx. 250 times the tidal forces of the Moon, at its closest approach, which would rapidly decrease on either side of that point. The effects of the tidal forces are much harder to ascertain than their strength, but - fwiw - my intuition suggests that'd result...

Do note, you have the lunar orbit going the wrong way. The only way in which it is retrograde, is in the context of its apparent motion on the sky as seen from Earth, w/r to the background stars. The orbit itself is prograde. Also, can you provide a reference using pro/retrograde to describe the...

While I'd take issue with your characterisation of local H0 measurements - they reach out to roughly z=1, so way farther than the scale of superclusters or the distances between them, i.e. reaching across the voids - and am not sure what line of thought have made you conclude the H0 should be...