Recent content by michelcolman

Wow, I didn't expect that.

Wow, for such a highly regarded astrophysicist he sure makes a lot of mistakes. This is not the first time I caught him saying falsehoods on his podcasts: - In another episode he said that the speed of earth is exactly right for it to stay in its orbit and that, if the mass of the sun were to...

So it is higher at the poles, but not quite as much higher as you would expect from simply plugging the smaller radius into Newton's formula of gravity. Got it, thanks!

From that wikipedia article I gather that gravity is stronger at the poles. So both Neil's explanation and the final result are wrong.

I don't think you understood my question. I know that, when you're inside a homogenous spherical mass, the outer shell exerts no net gravity on you. I did the full calculation during my engineering studies, and it all cancels out so only the sphere from the center up to your position has a net...

I just saw a StarTalk video where Neil deGrasse Tyson says that gravity at the poles is lower than at the equator because, even though you are closer to the center, the mass around the equator outside the sphere below you somehow does not count (skip to 4:21 in the video). He is obviously wrong...

But why would that be exactly? If you hold the end of the hose higher, the water will come out with less pressure (and at some height no water will come out anymore at all). If you lower the end, it will have more pressure. Under water, the pressure from the water in the pool will go up by the...

It just occurred to me that I could do a very simple experiment: timing the revolutions of the water meter. Turns out the flow rates are practically identical after all. I guess the hose being "sucked in" is due to the water flow dragging the surrounding water along with it, resulting in a flow...

I just noticed something interesting: if I hold the hose immediately above the water and then slowly lower it into the water, it quite abruptly moves down into the water, appearing to be "sucked in". Of course no actual "sucking" is taking place, but this rather seems to indicate that the...

It's from a standard water faucet, so I imagine the pressure at the faucet is determined either by the height of the water tower or the output of some huge pump supplying the neighbourhood. So I think we can assume the pressure to be constant at the faucet. Which means the pressure at the outlet...

Don't reply too quickly, I've seen a lot of answers on this question already (differing ones of course, what would you expect), at first sight it would seem to be really simple but there are quite a few complicating factors. So the question is basically: what's the quickest way to fill up a...

Still semantics. We use the word "reality" to mean different things. When I used the term, I really meant "subjective reality", i.e. reality as observed using that reference frame. Einstein said any observer can describe reality with his own coordinates and use the same physical laws to arrive...

Those are extremely interesting links. If I understood correctly, I was not crazy after all, but just neglected to take certain factors like gravity into account. In an empty universe (or a universe containing only massless objects), my description would be more or less valid, FRW with...

Thank you, your post makes a lot of sense. So, if I understood correctly, my description would work if the universe consisted of massless galaxies that were being pushed apart by an infinite army of equally massless angels. However, because of gravity, dark energy and other effects, the...

OK, forget about the curved universe for a minute, let's first clear this up. Lorentz contraction is indeed "just a change in coordinate convention", and so is time dilation. Still, they lead to very real and measurable results. When I say "M31 moves into the future during this acceleration"...