Recent content by Halc

It would indeed then be an invariant that the barn doors both close. It just wouldn't be an invariant that those doors are closed simultaneously.

That is perhaps our disconnect, using the same language to describe both linear and rotational effects. Come on now, that's a coordinate effect, not a physical one, since the pole does not fit in the barn in frames where the barn moves faster. The whole scenario is just an exercise in...

It does happen in any frame: The fitting of more objects on the circular track. OK, the size/shape of the track and the size of any specific object moving along it is all frame dependent. It's how many more you can pack in that is invariant. Likewise, consider two identical thin rings (thin...

The one I linked, indirect through usenet, on math.ucr,edu Best one is this "Real (not pseudo) gravitational time dilation (i.e., fields due to matter) is a different story. These fields are never uniform, and the derivations just mentioned don't work.". This explicitly states that since the...

Thanks Perter for the replies. I was unaware that 'gravitational strength' and 'gravitional potential' meant the same thing. The topic did not make it that clear. I took 'strength' to mean how much the potential changes locally over distance, the derivative of the potential. I could not find...

This topic is not about the pinned pages, but I went to the dilation page on the FAQ and it seemed incomplete. https://www.physicsforums.com/threads/time-dilation-definition-what-is-time-dilation.763074/ A quick review since the page is locked "Time dilation is the factor by which an inertial...

There was that rabbit...

Indeed. To illustrate, I did a spacetime diagram illustrating the view of the tunnel from a moment in time when the train is sticking out both ends. The stationary train is the red bar at the top. I did not show its position in the past since it doesn't move, so the lines would go straight...

They're called natural units and we're all fine with them. I thought the question was if anybody on the train experienced total darkness. The spacetime diagram would really help with that problem. Figuring out what the mid-tunnel guy sees when the middle of the train is in his presence is not...

Sounds good. It puts the front at x=8 1.33 time units later. That seems wrong. In 25 (seconds?) the back will move 25*0.8 = 20 putting it at x=0, not x=2 at t=10 Notice that the train back (any part approaching) appears to move faster than c to the mid-tunnel observer. Now at t=10, is that...

One queen can move to 21 to 27 squares depending on where it is, and assuming it is nowhere blocked. Not sure where the 56 comes from. A crowded board with lots of queens will have many otherwise legal moves blocked, plus one has to for the most part avoid putting either king in check, which...

Not a model change it seems. The ring (sort of elliptical at first) is there the whole time and I think the merger was placed off-center deliberately to show a portion of it. The stars appear to move in opposite directions on either side of it. The stuff right at that 'ring' appears to move the...

Excellent and informative video. I've seen similar simulations of the PoV of an observer falling into a very large black hole, the very interesting thing being that there is nothing weird that occurs at the event horizon. If the narrator doesn't tell you when it happens, you'd never know. So...

Indeed. Fave track to date is Shine On You Crazy Diamond VI, something no radio station ever plays unless they're doing the whole thing. Other notes: I've always referred to part V as the flying saxophone song and always figured it was double tracked or two players or something since nobody can...

Why not? All you need to do is get close enough to its photon sphere. OK, i don't think even a neutron star can be sufficiently dense to let you get that close, so is the restriction that it is still something commonly referred to as a 'star'? Of course the tidal forces will kill you (unless...