Images of black holes

[Oniya]

You're thinking of the 'light cone' in diagrams of space-time.  That has to do with what you are capable of observing, and doesn't translate to a physical cone at all.

[Vekseid]

Isn't the universe in a cone shape though?

The Universe is flat to measurement error.

[Oniya]

The Universe is flat to measurement error.

To expand on this, if you were to use laser sighting to mark out a ginormous triangle in space, and measured the angles, you would get so close to 180 degrees that you couldn't tell the difference.

If the universe was curved like sphere or saddle-shape, such that the shortest distance between two points was not a straight line (think of airplane routes from the US to Russia), then the angles would be significantly different, like the triangle formed by the equator, the Prime Meridian, and any other line of longitude.

[bennyg4444]

To expand on this, if you were to use laser sighting to mark out a ginormous triangle in space, and measured the angles, you would get so close to 180 degrees that you couldn't tell the difference.

If the universe was curved like sphere or saddle-shape, such that the shortest distance between two points was not a straight line (think of airplane routes from the US to Russia), then the angles would be significantly different, like the triangle formed by the equator, the Prime Meridian, and any other line of longitude.

Ah, the sound of non-euclidian geometry. It makes my brain confused and enraged at the same time. Besides, the point of those measurements is to try and put "imperceptible" dimensions into "understandable" terms. It all goes back to the Flatland thought experiment.

[Oniya]

Spherical geometry (the airplane example I used) is probably the easiest of the non-Euclideans to understand, simply because it's got a physical analogue, both for the triangle definition and for making it expand (blowing up a balloon - no point on the surface is the 'center', and in fact, to any observer embedded in the surface of the balloon, they are the center of expansion).

If Flatland is more your cup of tea than cosmology lectures, there's a guy named Rudy Rucker who has a fabulous book called 'The Fourth Dimension' - fairly sure there's not an equation in the book, and it's got illustrations that remind me of James Thurber.

[bennyg4444]

I appreciate cosmology just as much the the mathematical laws that concern cosmological matters. The fact of the matter is that it's basically the same conversation if you begin talking about the properties of celestial bodies, and their subsequent positioning in the universe. I mean, look at the gravitation effect of a black hole on light. There's no way you can even bring up a black hole without talking about that property because it's where it gets its name.

[bennyg4444]

Oh, and thank you for the book suggestion, it does sound up my alley. I'll put it on my list after A Brief History of Time. :P

[Frost]

http://phys.org/news/2012-06-gas-cloud-collide-galaxy-black.html#nRlv


and ...


http://phys.org/news/2013-06-gas-cloud-reveal-black-holes.html