Dark Energy

[Sparko]

Yep. As always, lots of technical details (most of which i don't understand), but that's the gist.

OK thanks. The bit about the varying redshift on the novas was what was tripping me up mostly.

[Truthseeker]

Did anyone watch the science channel show on Dark Energy last night?

I would like some of you physics nerds to explain a few things for me.

Basically what I got out of the show was that by measuring 42 supernovas, and it was found that some of the novas were more distant than they should be so that means the universe's expansion is accelerating. And the force that is causing the acceleration is unknown so they call it "dark energy" for now.

So first, how do they know WHERE the supernovas SHOULD have been in the first place to determine that they were "farther away than they SHOULD be" - basically if a supernova was at 1000 light years when observed, how can they say that it really should have only been 100 light years away (as an example)? Supernovas happen all over the universe at different distances and at different times. I mean if all supernovas happened 1 Billion years ago, then you would expect all of the supernovas to be 1 billion light years away and if some were 1.5 Billion LY away then you could claim that the universe has expanded faster than it should. But since you can't claim something like that, how do they know how far a supernova should be and that it was too far away?

Second, it is claimed that the universe is a hypersphere, and a 3D example often used is the skin of a balloon with dots drawn on it, to show the galaxies expanding away from each other. Yet on a balloon as it gets larger and larger (basically expanding at the same rate, the distance of the points on the skin will move away from each other faster and faster because the surface area is a lot larger than when the balloon was small. Wouldn't that translated to the hypersphere explain the acceleration of expansion without having to resort to dark energy?


Thirdly, if the universe is expanding at an accelerated rate, does that mean that it isn't really 14 billion years old? Wasn't that calculated by the expansion rate of the universe when they thought it was steady?

Scientists had a model of the universe and made predictions with it. If a sky object was x parasceconds from Earth, then y years later it would be (x + d) paraseconds away, where d is a positive number, according to the model. But, lo and behold, the object is observed to be much more distant than predicted. Why? One guess is dark energy, to make objects go faster than otherwise.