View Full Version : Discussion: Survey Confirms Dark Energy Theories

2004-Sep-04, 04:30 PM
SUMMARY: Recent evidence seems to indicate that the expansion of the Universe is actually accelerating - some kind of "dark energy" is pushing it apart. And a new redshift survey of galactic clusters seems to support this. Astronomers using data gathered by the Chandra X-Ray Observatory have determined that there is insufficient matter (both regular and dark matter) in various galactic clusters to account for their shape and position, so something else must be having an effect.

What do you think about this story? Post your comments below.

2004-Sep-05, 12:41 AM
What about the simple, basic, classical fact that the geometric spacetime of the universe is expanding on its own? Why do we have to make up something else that does the exact same thing?

2013-Mar-31, 09:04 PM
Wouldn't vacuum energy have mass? Would that explain the missing mass (dark matter) and the missing force (dark energy) at the same time?

If dark energy is pulling us apart, why can't we detect it in any of our experiments on a local level? Galaxies, solar system and planets? To say that it only acts on cosmic scales and not be able to detect test it on a local scale seems like a fail for dark energy.
One thing I've been contemplating is, where are we in the universe and depending on where we are and what we are observing, wouldn't that effect the interpretation of what we observe? For example if we're on one side of the universe looking across at the other side, then things are going faster because your side and the other side are both moving away from the centre. However if you're on one side looking sideway at another part, it's going away at an angle from you, and the speed you're difference is less than the first.

I've never heard anyone mention our position relative to the centre of the big bang. People conveniently say that the expansion is uniform, but if there's an explosion, then everything goes out from the centre and what you see is relative to where you are in the explosion and where the other object you're looking at is from the centre of the explosion.
One final thought. Could there be a massive black hole formed at the centre of our universe when things were first coalescing? Why wouldn't a black hole form with such a massive amount of material forming during the big bang. (It's just a larger version of a supernova, most material is going out, but some forms a black hole in the centre.)

John Mendenhall
2013-Mar-31, 11:47 PM
Re replies 2 and 3, the problem is that the expansion is accelerating, and there is no center of the universe. The idea of expansion from a point is popular science crock. The observable universe is expanding from a much denser state, NOT from a point.

2013-Apr-01, 12:49 PM
What do you think about this story?

Um, where's the story?

Wouldn't vacuum energy have mass? Would that explain the missing mass (dark matter) and the missing force (dark energy) at the same time?

Yes, any energy has some mass, and vacuum energy may very well have something to do with dark energy, but not dark matter, which is distributed around galaxies and clusters. Both dark energy and vacuum energy are apparently distributed pretty evenly throughout the universe.

2013-Apr-01, 01:45 PM
Um, where's the story?.Maybe things were different in 2004 when he posted that.

2013-Apr-01, 05:53 PM
Maybe things were different in 2004 when he posted that.

Definitely. The universe was smaller and more dense.

2013-Apr-01, 07:21 PM
Definitely. The universe was smaller and more dense.

....but apparently I'm still pretty dense not to have noticed the date of the post. :doh:

2013-Apr-01, 08:12 PM
Test failed! I missed the OP for most of a decade. :)

I am not sure I understand Dark Energy at all, but I think it is pushing parts of the universe apart by virtue of the distance between those parts, so this is unlike an explosion. Obviously, this is insanely simplistic, otherwise I wouldn't understand.

When I first heard of it, I thought it was crazy. After a while, it occurred to me that it makes perfect sense, if the universe started expanding and nothing changed, where did the "expansion magic" go?

I am really surprised it wasn't thought of a long time ago. It is sort of like saying water seeks the lowest point and being horribly surprised that water continues to do that after you float a few ships on it.