Black Hole Explorer

A Slide Rule, a Sundial, and a Physicist walk into a bar
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testtubegames
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Black Hole Explorer

Post by testtubegames » Thu Sep 20, 2018 1:39 pm

The distortion of space (and especially time) around black holes is fascinating to me - so I made an experimental little sim, to see if I could recreate that.

https://testtubegames.com/ShareBox/blackhole/

Move around, explore the space, and add (or shoot, if you're moving) Beacons to see how clocks tick differently.

For reference, you're moving in a 2D slice around a black hole... with the grid lines representing polar coordinates, and the surface of the black hole being the circle at the bottom. Oh, and there aren't any forces present, at least not yet -- everything there moves at a constant velocity. It's more about exploring the coordinate space. Imagine everything has rockets that counteract any forces they encounter.

It's the first time for this project to see the light of day, so I'd appreciate any feedback about it (what was confusing, or worked, or what might make it more helpful as a tool for exploration).

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Re: Black Hole Explorer

Post by testtubegames » Sat Oct 13, 2018 5:40 pm

Made an update to the sim -

now with:
-gravitational forces!
-fly around
-fire various types of objects
-lasers!

Posted at a new url: https://testtubegames.com/ShareBox/blackhole2/

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Re: Black Hole Explorer

Post by testtubegames » Thu Oct 18, 2018 5:05 pm

Update - new and improved, and posted in its new home:

https://testtubegames.com/blackhole.html

aman
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Re: Black Hole Explorer

Post by aman » Sun Dec 02, 2018 12:53 pm

Hi I really like your gravity simulator and black hole explorer games. I just noticed a small error in the black hole explorer game and wanted to get your opinion on it. It seems like the game is taken in the perspective of the rocket that you control. When you drop a rock into the black hole the rock is radially length contracted as you would expect from your perspective. But when you bring yourself closer to the black hole you appear length contracted but I think this is incorrect. From your own perspective you never notice your length contraction. Instead you would notice radial length elongation of things farther away.

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Re: Black Hole Explorer

Post by testtubegames » Tue Dec 04, 2018 11:27 am

aman wrote:
Sun Dec 02, 2018 12:53 pm
From your own perspective you never notice your length contraction. Instead you would notice radial length elongation of things farther away.
That's a good point you bring up - you wouldn't notice yourself shrink.

The view you're looking at is one way of representing the Schwarzschild metric - with the 'radii' being drawn accurately, and space otherwise kept flat. This representation doesn't preserve distances, however, which is why closer things seem to shrink radially.

To give a 'simple' answer, I'd suggest you check out the 'embedded' view (toggle in the top right). This shows the classic funnel perspective of a black hole, and it's a representation that accurately shows distances. So you won't see objects shrink at all, but rather just tilt along the curved spacetime. This view probably does a better job of showing off what you'd see if you were there, since if you zoom in close enough, spacetime show appear flat, and indeed it would in the embedded view.

That's not a perfect answer, though, since now you have me wondering exactly what is being shown. I guess (in the non-embedded view) you might be seeing a representation of what an outside observer (far from the black hole) would see measure, with the caveat that the *time* is ticking as it would for an observer inside the rocket ship.

Once you get to what the observer in the rocket ship would actually see, there I'm not sure there's an easy answer. In some sense, would they see objects further from the event horizon be stretched radially? I'm not sure. Of course, 'seen' and 'measured' are two different things. The observer in the rocket *would* measure themselves as the same size as always... though they would also measure themselves as being fewer units of 'radius' high, using schwarzschild coordinates. (So perhaps it's most accurate to say you're seeing what the observer in the rocket would *measure*).

And then we you get to what they'd see... you'd need to figure out the paths that photons would take to reach them, and that kind of raytracing and gravitational lensing (with multiple images of each thing) hits above this sim's paygrade.

One thing I'd like to do (and your comment gives me another push in that direction) is write out exactly what the sim is showing -- to make it clear what aspects of GR are being accurately rendered (and how).

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Re: Black Hole Explorer

Post by Sagarika579 » Fri Apr 26, 2019 5:44 am

Black Hole is a quite interesting topic!!!

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