Saturday, April 28, 2012

Left Side of the Aisle #54 - Part 3

And Another Thing: Some cool science bits from life on Earth to life among the stars

Sunday, April 22, was the 42nd Earth Day, started in 1970 by Senator Gaylord Nelson. I remember the first Earth Day; I skipped classes - I think integral calculus was one I missed - to spend the day on 14th Street in New York.

Earth Day is a good day to be reminded of how much we have yet to learn about Earth. For one thing, undiscovered species are still out there. Lots of them. Over the past year, researchers have found seven new forest mice species in Philippines, a a “psychedelic” gecko in Vietnam, and a new type of dolphin in Australia. They also found in the Philippines four new species of crab that sport some wild colors: That one over there is not a false color image; the crab really is purple with pink claws.

A purple crab. Now that is cool.

But moving out from Earth, you have probably seen one of the devices pictured here, at least on TV. It's a tricorder, and it was a staple of the Star Trek universe from the original series right through The Next Generation, Deep Space 9, and the rest. It was used by Spock, Sulu, Geordi, Data, and the rest, including a good number of redshirts, A truly remarkable instrument, it could do pretty much anything the plot required: It could measure the atmosphere of a new planet, show composition of rocks, and far more. In Sick Bay it could be used to identify diseases and examine injuries.

Well, a tricorder is still a long way in the future, but we might have taken a tiny step closer to one. The picture just below is of a hand-held X-ray machine. Not some big, honking device taking up its own room but one you literally can hold in your hand.

There is a phenomenon in physics that involves producing electromagnetic energy, i.e., some form of light, by purely physical means. You can try it yourself: Take some adhesive tape into a nice dark closet and pull some tape off the roll very hard, very fast. With some luck you might see little flashes of light. Those are not optical illusions, you really have generated light by pulling a piece of adhesive tape. This device, under development, apparently uses a version of the principle to produce X-rays, which are even more energetic than visible light.

Because is so small it can be carried around and it is focused enough to limit dangerous, unnecessary exposure to the X-rays, if successfully developed it could be used in multiple ways: It could, for example, diagnose a bone fracture right on the spot. It could determine the metallic composition of a piece of jewelry. It could find a stud in a wall.

On there other hand, there is a downside: The first experience most of us would have with such a device would likely be seeing it in the hands of a cop who stopped us for speeding or some such thing and now wants to X-ray us and our trunk.

Leave that downer aside for the moment. Since I've already brought up Star Trek, let's move out into space.

The picture on the right is of a galaxy cluster. The blue halo is an overlay showing where the dark matter should be.

Dark matter?

Dark matter. It's one of the great mysteries in cosmology.

Einstein's General Theory of Relativity explains how gravity works. In the simplest possible terms, mass causes space (actually, spacetime) to warp. It's often pictured by imagining a stretched rubber sheet with balls of different weights placed on the sheet, causing it to warp in different ways. At the same time, the warping of space (spacetime) affects the paths bodies take as they move through space(time). Think, for example, how your movement changes going over hilly terrain as opposed to a flat surface. Physicists say that "mass tells spacetime how to warp; spacetime tells mass how to move."

Anyway. The point is that astronomers look at stars in galaxies and at groups of galaxies and observe how they move. Using relativity, they can say how much mass must be present - and therefore how strong gravity must be - to make them move the way they do.

Here's the problem: The amount of mass we can see not enough - not nearly enough - to explain the motion we see. In fact, we can see only about 1/6 of what would be required. That remainder - that 5/6 of stuff which we can't see - is dark matter.

Exactly what dark matter is, we don't know. There have been lots of candidates but they all failed to explain enough. The most generally accepted idea among scientists now is that dark matter is composed of a new type of particle, one that interacts normally with gravity but only very weakly with the other known forces of the universe. That particle has not been found; until and unless it is, dark matter remains a mystery.

And it just got more mysterious.

According to accepted ideas, the neighborhood around the Sun should be filled with dark matter. Billions of these particles should be rushing through us every second. But the most accurate study yet of motions of stars in the Milky Way, recently completed, has found no evidence for dark matter in a large volume of space around the Sun. That is, the matter we can see can account for the motion we see, leaving no sign of dark matter.

No one knows why. It could be that a bigger survey, now planned, that will examine the motion of millions of stars instead of just hundreds, will show the evidence of dark matter which this one didn't. On the other hand, it's also possible that the whole idea of dark matter is wrong. The trouble is, none of the alternatives are even as good.

One such alternative, called Modified Newtonian Dynamics, tweaks how gravity works at large scales. But not only does it not explain as much as the idea of dark matter does, it also would be contradicted by these latest observations.

Another alternative is MOG, or "modified gravity." which involves taking relativity and adding three new fields, one of which has mass and therefore an associated particle. The problem here is that instead of invoking a new, unknown particle à la dark matter, it invokes these three new fields and still has to add a previously unknown particle to give mass to one of the new fields.

Then again, it could be that the idea of dark matter is correct but that the particles involved in dark matter behave somewhat differently than thought or are distributed in space somewhat differently than thought.

Or it could be that the latest observations are just wrong.

The thing is, right now, nobody knows - but we do know that current observations challenge the hypothesis, which raises new questions to be answered. It's a good reminder that science is not about knowing the answers, it's about how you find out the answers.

One more leap outward. On Earth, all life is dependent upon the nucleic acids DNA and RNA. The chemical structure of nucleic acids isn't all that complex: It's the now-familiar double helix, consisting of two long polymers of sugars linked together by phosphates. Hanging off each sugar is one of four bases. It's the order of those bases which provides the genetic information.

The question is, did it have to be that way? The perhaps surprising but surely exciting answer is no.

The phosphate can be replaced by a sulfate and the resulting molecule can still transmit genetic info back and forth with regular nucleic acids. You can replace the sugars with related, ring-like structures, and it still works.

Now, this works in the lab but not in actual biological systems because the enzymes that prepare and copy DNA, for example, will only work with the sugars and phosphates. But there is no reason that other enzymes could not work with other chemical structures. Which means we have proof - not a hypothesis, but proof - that life does not have to be life as we know it and life on Earth using sugars and phosphates rather than some other possible combination may have been just by chance.

It also means by increasing the ways that life can function, it also increases the ways it could have started on any given planet. With current estimates of the number of habitable planets - defined as rocky planets neither too cold nor too hot for liquid water - in our galaxy alone running to the tens of billions, the chances there could be a Horta out there somewhere are going up.

And that is even cooler than a purple crab.


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