I just watched a fascinating show on the National Geographic Channel about dark matter and dark energy.Ã‚Â
Here is a quick synopsis:Ã‚Â The standard theory of gravity predicts that the further an object is away from a massive object, the smaller the gravitational effect the massive object will have on the object.Ã‚Â In the solar system this means that the distant planets will orbit the sun much more slowly then the closer planets, and sure enough empirical observations confirm the theory.
Problem 1:Ã‚Â In the 1970Ã¢â‚¬â„¢s it was observed that the theory does not work at the level of galaxies.Ã‚Â The stars and gas at the outer edge of galaxies orbit at the same rate as the ones closer in.Ã‚Â
Solution 1:Ã‚Â The concept of dark matter (objects with mass that do not consist of atoms) was developed to account for this.
Problem 2:Ã‚Â Experiments to measure the amount of dark matter revealed there was not nearly enough to account for the data.
Solution 2:Ã‚Â Observations designed to find out how much the expansion of the universe is slowing found out just the opposite.Ã‚Â The universe is expanding at an increasing rate.Ã‚Â The concept of dark energy was developed to account for this, and it turned out that the amount of dark energy was exactly the right amount to account for the Ã¢â‚¬Å“missingÃ¢â‚¬Â dark matter.
From these observations came the so-called Ã¢â‚¬Å“standard modelÃ¢â‚¬Â of cosmology.Ã‚Â The universe consists of 4% regular atoms, 21% dark matter, and 75% dark energy.
Note:Ã‚Â A small minority of scientists believe that the dark matter and dark energy theory is not necessary.Ã‚Â They believe that the data can be explained by Ã¢â‚¬Å“variable gravity,Ã¢â‚¬Â the notion that gravitational force is not constant throughout the universe.
If I got this wrong, IÃ¢â‚¬â„¢m sure one of our cosmologist readers will set me straight.Ã‚Â
The part of the show that I found most interesting was an interview with Professor Mike Disney, the longest serving member of the Hubble Space Telescope advisory committee.
Professor Disney is skeptical of the standard model, and he says something very profound:Ã‚Â Ã¢â‚¬Å“The greatest obstacle to progress in science is the illusion of knowledge, the illusion that we know whatÃ¢â‚¬â„¢s going on when we really donÃ¢â‚¬â„¢t.Ã¢â‚¬Â
Disney is also unimpressed by computer models that purport to prove the standard model.Ã‚Â He says, Ã¢â‚¬Å“LetÃ¢â‚¬â„¢s suppose I say I saw a pink elephant.Ã‚Â If someone does a computer simulation showing a pink elephant, no one will believe it, because he could have just as easily twisted a few knobs and demonstrated a green elephant.Ã¢â‚¬Â