Sunday, April 19, 2009

Dark Murmurings

It is a good thing to proceed in order and to establish propositions. This is the way to gain ground and to progress with certainty. ~ Gottfried Leibniz

I am so tired of dark energy.

It's not that I'm dead set against the concept. The idea that we haven't discovered everything resonates with me. Whether it's dark energy or dark matter, in a huge universe that's 15 billion years old (give or take), there are bound to be things we haven't found. It's just that I am so tired of dark stuff being invoked every time someone can't explain something.

Worse, dark energy seems now to be a variable entity, at least according to this study. This idea has come up before in a different context, but actual data didn't support the "flipping" of dark energy from attractive to repulsive.

Perhaps it's the theory that's repulsive.

At any rate, now it seems that the increasing acceleration of the universe is actually slowing down, which is what people used to think was happening. The culprit in this new plot twist is, once again, the measurement of distances to supernovae.

It is assumed, based on a lot of observations, that certain types of supernovae all have the same intrinsic brightness. Therefore, if you see a supernova in a galaxy far, far away, you can measure its brightness, compare that to what it would be at a known distance, and calculate the actual distance to the object. Then you can look at the red-shift of the spectrum of the supernova and determine how fast it's traveling.

In this case, that resulted in some numbers that didn't fit the current theoretical flavor of the month.

Now, it's possible that there could be problems with the data. For example, some of the supernovae could be partially obscured by clouds of gas and dust. In that case, the observers make corrections for the amount of dimming caused by the intervening stuff. Perhaps the adjustments weren't correct.

The thing is, the same arguments could be made for the original data that determined that the universe's expansion was accelerating. Or it could be possible that, in fact, supernova luminosities have changed over billions of years. It could be that the chemistry of stars has altered over time, with the result that older supernovae are brighter or dimmer than we would expect.

Then there's the problem of the voids.

One of the assumptions of physics and astronomy is that there's nothing special about our place in the universe. So that, as we look in different directions at different objects, nothing is affected by where we happen to be. This would be fine, except that the more we look at the universe, the less homogeneous it is. I first brought this up in a discussion of the Swiss Cheese theory of the universe. Some time later, this article popped up, raising the same sorts of questions.

Now, another survey of the sky has been taken that once again raises the issue of apparent huge voids in the universe. Keep in mind that this survey covers only six degrees of the southern sky, so stranger things could await us. If nothing else, it could be found that one of those voids is home for the Milky Way.

If that's the case, a lot of theories about dark matter, dark energy, and the expansion of the universe end up needing to be reworked. One nice thing is that non-homogeneity would pretty much get us out of this business of constants changing over time. If in fact our place is not exactly the neighborhood we thought it was, that would explain why things look different to us than we expected. It's sort of like those perspective tricks that are played on the eye, where the relative sizes of objects are not what they seem.

In the case of space, it's gravity that may not be affecting us or observed objects to the extent we believe they are.

The data collecting will continue, and it's quite possible that real life is going to turn some speculations about dark stuff on its ear. It's also possible that it could provide some details that could finally give us a handle on what the dark stuff might be, if it does exist. It wouldn't ruin my day to find that dark energy and dark matter were at least partially defined, because getting to that point would allow cosmologists to finally begin to hone some of these theories. I also suspect that a lot of inconsistencies would start to disappear.

And I'll bet through all of it that Einstein's theories still stand strong.

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