Category Archives: astronomy

Predictions of physics theories

Over at Cosmic Variance, Sean Carroll posted yesterday about a straw poll taken at a small gathering of physicists who focus on the cosmological theory of inflation, asking them what they thought the likelihood of the general principle of the theory being true was. He noted that his estimate of of 75% chance was on the low side compared to the majority of the people attending the conference who put the likelihood of inflation being a fact at around 90%. After the conference, he asked several of his colleagues at Caltech, and found that many of them, none of whom were directly working on inflation, put the likelihood at only 25%.

He then asked his readers to present their own estimate for the probability that inflation was true. And he added a few other major theoretical concepts in physics: supersymmetry, string theory, the Higgs boson, large extra dimensions, WIMP dark matter, and “any non-cosmological-constant explanation for cosmic acceleration.” He left the categories quite vague (for example, does “large” mean, “micro/macroscopic” or just “larger than Planck length”) because there are often multiple theories within each category, but for the most part there is a single unifying concept for each theory.

60+ people with a wide range of backgrounds have responded with their estimates now. And the results are interesting in a couple of ways. The two charts below show the how many people proposed specific percentages of the likelihood of each theoretical concept. The interactive versions are available on GoogleDocs.

Compiled likelihoods of several physics theories, based on predictions given by commenters at Cosmic Variance

Compiled likelihoods of several physics theories, based on predictions given by commenters who indicated an educational/professional background in physics at Cosmic Variance

The first things that jump out at me are that pretty much no one believes that large extra dimensions have any chance of existing (average likelihood being 9.08% with a standard deviation of 15.47), while the Higgs particle is considered quite likely to exist (average = 79.52%, std dev = 26.77), with inflation also having a better than 2/3 chance (average = 67.02%, std dev = 28.81). Amongst those who claimed an educational and/or professional background in physics (and astronomy), large extra dimensions are considered similarly unlikely, but the Higgs boson, inflation, and WIMPs are both considered ~10% more likely than by the commenters as a whole.

On the other hand, the chances given to supersymmetry, string theory, and non-cosmological-constant cosmic expansion are all stable in being considered relatively unlikely by both laymen and scientists alike.

It’s an interesting little bit of meta-analysis, really, which raises some questions about why certain major theories are accepted both in and outside of those educated in physics, why some of those are more accepted within the subset, and why other theories are considered equally less likely, regardless of education. It is likely that “insiders”, as it were, have a firmer basis in the fundamentals of physics and so they are better able to evaluate the theories themselves, which would explain the variation between the insiders and outsiders on certain topics. But I don’t think there is anything about the Higgs boson, or inflation, or WIMPs which differentiates them from the other theories that makes them less comprehensible to those with a physics background.

And since this is a non-rigorous, loosely defined survey, I wouldn’t really want to try to draw any significant conclusions from it. But it is interesting to get a general picture of how various theories are viewed and accepted within the physics community as a whole, and amongst the larger population of laypeople who are interested in modern advancements in the science.

Update 2/11/2011: Over 100 people have commented now.

Inflation SuSy Strings Higgs
Avg Std Dev Avg Std Dev Avg Std Dev Avg Std Dev
Everyone 66.79 28.63 44.07 30.24 30.52 30.47 76.96 27.41
Physics Background 71.43 22.13 45.56 27.99 25.37 26.83 85.32 20.61
Difference 4.64 -6.5 1.49 -2.25 -5.15 -3.64 8.36 -6.8
large xtra D WIMPs non-CC exp
Avg Std Dev Avg Std Dev Avg Std Dev
Everyone 11.76 20.01 58.41 29.36 27.74 28.38
Physics Background 8.54 14.67 60.84 25.48 25.07 25.01
Difference -3.22 -5.34 2.43 -3.88 -2.67 -3.37

Compiled likelihoods of several physics theories, based on predictions given by commenters at Cosmic Variance

Compiled likelihoods of several physics theories, based on predictions given by commenters who indicated an educational/professional background in physics at Cosmic Variance

It’s a crowded neighborhood!

It seems that every time you turn around these days there is a news story about astronomers discovering new extra solar planets. I was even remarking the other day that I really don’t remember it being a big deal in the media 15 years ago when the first such planet was discovered. But of somewhat more immediate importance is the search for near Earth objects — asteroids.

With movies like Armageddon and Deep Impact, the question of why locating asteroids is important is something that is fairly obvious to most people. And Phil Plait just hosted a new show on Discovery Channel called Bad Universe that takes a look at the science behind asteroid and comet impacts. But just how many asteroids do we know about and how much are we doing to find them?

Well, a week ago, a video was released that mapped the location of all the asteroids discovered since 1980.

It’s a rather hypnotic video, really. But it is somewhat deceptive. Nothing other than the planetary orbits is depicted to scale. Each asteroid is a pixel, but the detectable asteroids range in size from several hundred feet to several hundred miles across. In the video, green dots are asteroids which do not pass close to the Earth any time soon, yellow dots are asteroids which are approaching the Earth but are not crossing our orbit, and red dots are asteroids which have crossed or will cross the Earth’s orbit. An interesting note to consider when watching the video is that until very recently we were only detecting asteroids that were located 180 degrees away from the sun in relation to the Earth. That’s because the primary way of finding them is the light reflected off them from the sun (in the same way that we can see the moon.) The more recent pattern of detection covers areas 90 degrees away from the sun thanks to a new satellite launched in 2008 or 2009 which is much more sensitive to the reflected light from asteroids in those areas.

So, as of 2010, there are over 500,000 known asteroids. Only 300 of those are on currently Earth-crossing orbits. The video is based on information put together by astronomers at Armagh Observatory, and there is a much more in-depth explanation of the information there. And they make a very important point that space is three dimensional — not all of these asteroids are on the same plane. They provide a close up of the asteroids within 0.3 AU (1 AU = the average distance between the earth and the sun) and use lines to show that each asteroid is either above or below the plane on which the sun and the earth both lie. The arrows show the direction in which the asteroid is moving and if the arrow extends from the bottom of a line, they are below that plane and if from the top of a line, they are above the plane, and the longer that line, the farther from the plane the asteroid is.