The December 19th Parade had an article by David Levy, of the
Shoemaker-Levy comet. In it Levy picked his “five discoveries
that changed us forever” in this century. They were (1) Einstein”s
relativity, (2) atomic structure and nuclear fission, (3) the
structure of DNA, (4) the greenhouse effect and global warming
and (5) the collision of the Shoemaker-Levy 9 comet with Jupiter.
At first, I thought it a bit cheeky of Levy to tout his own
discovery but he does have a point. Just as the global warming
work is a wake-up call for us to mend our profligate ways, the
mind boggling explosions when that fragmented comet hit Jupiter
are a wake-up call that earth is still fair game for another species-
destroying strike by a celestial wanderer. This is one type of alien
that really should worry us! The world needs more effort on the
problem of detecting and diverting such an alien from our planet”s
vicinity. I saw a bit on the news a few weeks ago about someone
who picked up a rock that just messed him or her. Speculation
was that it was part of the Leonids meteor shower. I knew there
was a reason I did not go out to watch!
Aside from these occasional wanderers, space has generally been
considered pretty doggone empty, the essence of nothingness.
However, “nothing” occupies the minds of many very bright
physicists these days. We touched in an earlier column on the fact
that what we think of as empty space among the stars in galaxies
is not empty at all but contains something called “dark matter”.
Indeed, some 90 percent of the matter in the universe is this dark
matter. I described in that column the use of the bending of light
by massive objects, such as galaxies, to “see” the distribution of
dark matter, based on a lecture I heard by Tony Tyson of Lucent
Technologies” Bell Labs. Nobody knows what this dark matter
really is, but it”s there. If it weren”t, stars would be flying apart
rather than spiraling around together in galaxies.
In the December 14th Science Times section of the NY Times
there is a report of the current status of the Sloan Digital Sky
Survey. The data from this intensive five-year survey of the
northern sky are only beginning to be interpreted, but already an
astonishing conclusion has been reached. The galaxies in general
seem to be about twice as large as they were thought to be. You
probably would think that a galaxy is as wide as the distances
between the outermost stars at opposite sides of the galaxy. But
remember, you can”t see that dark matter! The Sloan data
indicate that the galaxies contain dark matter that extends far out
into space, way beyond any visible features of the galaxy. A run
of the mill galaxy is now believed to extend a million light years
into space and weigh as much as a trillion suns. Most of this
weight is, of course, dark matter, far from being nothing.
Buried somewhere in one of my columns is the offhand statement
that our own Milky Way galaxy is on a collision course with the
Andromeda galaxy. I assumed that the encounter was far enough
in the future that I really didn”t have to worry about it since
Andromeda is 2 million light years away. However, with the
expanded galactic sphere of influence of the dark matter, there is
now speculation that our two galaxies are already touching way
out there in space. Our moviemakers should have a field day
when they realize we”re part of a galaxies-in-collision scenario.
Let”s talk more about space and “nothing”. A couple weeks ago,
I wrote about a professor at Dickinson College, my
undergraduate alma mater. Now, I find myself writing about the
work of another professor, this time from the University of
Pittsburgh (my graduate alma mater). This professor, Carlo
Rovelli, had his picture on the front page of the Science Times
section of the Pearl Harbor Day edition of the New York Times.
Professor Rovelli is, of course, working on the physics of nothing.
This is not the nothing of dark matter, which we have seen to be
far from nothing since it comprises all but a paltry 10 percent of
ordinary stuff in the universe. Instead, Rovelli is concerned with
space and time.
Let”s consider space first. If we think about space, one of our
common beliefs is that it is continuous. I admit that I never really
delved deeply into this belief and probably you haven”t either.
But, consider the following. If you want to measure the distance
between two points, you get a ruler and measure it. If you want
to measure the distance between transistors on a silicon chip you
get out your microscope and use some kind of scale to do the
measuring. If you want to measure the distance between the
silicon atoms, you might get out your scanning probe microscope
we discussed in an earlier column. What am I trying to say? It”s
that no matter how small you go, in principle at least, you could
come up with some way of measuring the distance between two
points. Carrying this further, between any two points you can
always pick out some more points between them to measure.
That is, space is smooth and continuous. Wrong!
It turns out that, according to the current thinking, there is a
smallest possible length, the so-called Planck length. Now, none
of us mortals are ever likely to run into this Planck length, which
is only ten to the minus 35th meters (a decimal point followed by
34 zeroes and a 1)! This is equivalent to saying that space is
quantized or, in other words, it”s got a grainy texture, the grains
being the size of the Planck length. Those of you who have read
my piece on string theory might say that such small sizes remind
you of those teensy strings. According to the Times article, the
string theorists find that if you have a circular string and you keep
reducing its diameter there”s a point at which you can”t reduce it
any more. The speculation is that this string diameter
corresponds to the Planck length.
Perhaps you”re the perceptive type who asks, “If we”ve quantized
space, what about time?” Well, if you”re truly perceptive you
might ask, “How much time does it take light to travel the Planck
length?” (I sure wasn”t smart enough to ask that!) The answer is
about ten to the minus 43 seconds (a decimal point followed by
42 zeroes and a 1). There”s your answer. This miniscule amount
of time is purportedly the smallest possible tick of any clock you
could ever devise. Time, then, also has a graininess to it, just like
space. To be honest, I”m pretty happy if my watch is correct to
within a minute or so, as long as I don”t miss the opening of
Frasier.
Back to Professor Rovelli, the picture in the Times is of him
gazing at a three-dimensional assemblage of interlocking rings
suspended from a structure of some sort. He is working on what
appears to be an alternative to the string theory called loop
quantum gravity. This is really weird stuff involving spinning
imaginary particles tracing round trips in space and something
called spin foam which consists of slices of the results of these
trips. I won”t even try to subject you and especially myself to
trying to understand this approach. Compared to loop quantum
gravity, string theory seems simple! However, if the loopists turn
out to be correct, at least we won”t be completely in the dark.
Speaking of the dark, let”s hope that those of you who have/had
to work over New Year”s will have or had no blackouts or
terrorist attacks to contend with and will curse/are cursing your
boss for causing you to miss that gala New Year”s Eve
celebration!
Allen F. Bortrum
