Dim Galaxy Could Give Clues to Dark Matter

chamblah writes "Reuters is reporting that the dimmest galaxy has been found. 'In fact, it is dimmest galaxy ever detected, which means it could give clues to the mysterious dark matter that appears to be pushing regular matter around.' Since this galaxy is '...100 times dimmer than the night sky', it could only be detected using 'instruments involved in the Sloan Digital Sky Survey, the sky-mapping project.' The galaxy is also part of the Andromeda galaxy, only 2 million light years from us. The article goes on to explain how finding these dim galaxies can be useful, 'Andromeda IX fits the profile for the small, dim galaxies that cosmic theorists predict should exist as leftovers from the formation of big galaxies.'"

Re:Dark matter or dark energy

[misterpies]

>>Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.

Well that sounds very neat and I'm sure any moderator with no knowledge of GR will mod you up. Unfortunately, though, if you do the maths you will discover that time does not run backwards inside a black hole. As someone pointed out, at the event horizon time does not stop for a local observer, but it appears to stop from the viewpoint of someone observing the horizon from outside.

Inside the black hole, what happens is even stranger than time running backwards. As you are no doubt aware, spacetime has 4 dimensions: 3 of space and one of time. Inside the black hole, the time dimension is swapped with one of the space dimensions - the radial dimension pointing at the centre of the hole. (For a spherical black hole, the maths is easiest in polar coordinates so your spatial dimensions are radial, axial and azimuthal rather than x, y and z). Because it's now a time-like dimension, and time marches ever onwards, you are inevitably drawn along the radial direction into the centre of the black hole; you can no more escape it than you can stop time locally. On the other hand, time has now become a spatial dimension, so presumably you can move along the time axis freely (until you hit the centre of the black hole and are crushed into nothingness).

That's what the maths says anyway. What it means philosophically (and biologically) to have your dimensions switched round is another question, and quite beyond my imagining.