Accelerating expansion of the Universe?Date: Thu May 28 08:40:04 1998
Posted by Tom Albergotti
Grade level: other
School: No school entered.
City: Orangeburg State/Province: SC
What are the implications of the accelerating expansion of the universe that was announced a few months ago? Has anything been verified? If so, what does it mean?
As it happens, I talked about this topic a couple of months ago at my website that I call Bitesized Astronomy. I'll copy that page here, and then make another comment at the bottom.
Week of March 2, 1998
We know that our Universe is expanding. As we look farther out, to more distant objects, we see that they are rushing away from us. It looks as if we are at the center of a gigantic explosion that made all the galaxies blow outward from us. This is an illusion; any galaxy would see the same thing. They aren't really moving away from us; we are all moving away from each other. We're not really at the center (as a matter of fact, there wasn't any center, but this is complicated enough!). Since we think this started some time ago in a huge explosion, we call the event the "Big Bang" (please feel free to check out the Relativity FAQ from the USENET newsgroup sci.physics.relativity!).
According to our best theories, we live inside a three-dimensional universe that itself is embedded in four dimensions. I know, that may make your head hurt, but don't worry about it just now. The point is, the overall Universe has a geometry, a shape, and we are not sure just what that shape is. Cosmologists (people that study these things) like to say that there are three different possible shapes to the Universe: open, flat or closed. If the Universe is open, it will expand forever. If it is closed, the expansion will eventually come to a halt, and reverse; in some far distant future the Universe will collapse again to a point. If the Universe is flat, it is forever balanced between open and closed; it will expand forever, but always slowing, just balancing gravity. We don't know for sure which of these three geometries describes the Universe best.
Now it turns out that studying SN will help here. Basically, if the Universe is open (will expand forever), closed (will eventually contract again) or flat (expanding just fast enough to balance gravity), you will see differences in the way the SN behave.
What Schmidt and Kirshner found is that the SN are dimmer than expected for their distance, which means they are farther away than expected. This was quite a surprise! We think we have a pretty good handle on how far away things should be, assuming nothing else has happened since the initial explosion which formed the Universe. But now it looks like something else is going on. The SN must have been pushed outwards by some force that has a negative effect on gravity. This is accelerating them.
Do I believe this? Not yet. Kirshner is a very good scientist, and so is Schmidt, so I expect they have done a very good job getting and analyzing the data. Is there something they forgot? Maybe, but I doubt it. More likely there is something going on here we don't understand. A repulsive force is the most palatable of the weirdnesses this implies. If this pans out, it has profound implications. I must stress though, that this is not a peer-reviewed article yet, but a preliminary announcement. It's more of a "what have we found here?" type of event. No doubt there will be more about this as time goes on!
Anyway, I have not heard any news since the initial press release about this, but I'm not surprised; this type of research takes a long time to confirm (or repudiate!). It may be a while before we hear more in the popular press, though I am sure a paper has been submitted to the Astrophysical Journal, one of the premier astronomical journals in the world for groundbreaking research like this! If and when I hear more, I will be sure to put more on my website, so feel free to check back there!