Ask just about any educated person today about the origins of the universe, and the terminology swiftly rolls off the tongue: Big Bang; background microwave radiation; 13.7 billion years.
But how much do we really know about the universe? One thing all experts agree on – and the general public seems to be completely ignorant of – is that we don’t know what makes up 96% of our universe.
In Genesis and Genes, I began the section on Dark Matter as follows:
Nobody – including astronomers and cosmologists – knows what the universe is made of. Visible matter – the kind of stuff that people and planets are made of – is outweighed by a factor of 6 or 7 by invisible, cold dark matter. To put it another way, something like 95% of the universe is made up of stuff we can’t detect, except that it seems to exert a gravitational pull.
I quoted numerous authorities on this subject, including the distinguished astronomer and author, James Kaler:
Our Galaxy, its stars revolving around the center under the influence of their combined gravity, is spinning too fast for what we see. Galaxies in clusters orbit around the clusters’ centers under the influence of their mutual gravities, but again, they move faster than expected. There must be something out there with enough of a gravitational hold to do the job, to speed things up, but it is completely unseen. Dark matter… We have no idea what constitutes it.
A popular history of astronomy weighs in with this:
Over 90 per cent of our Universe is invisible – filled with particles of mysterious dark matter. And astronomers have no idea what it is.
Nobody knows anything significant about what makes up more than 90% of the universe. And this is acknowledged even by those who pretend to be able to answer ultimate questions in naturalistic terms. Lawrence Krauss is a world-famous physicist and an ardent atheist. His latest book, A Universe from Nothing: Why There Is Something Rather than Nothing (Free Press, 2012) was reviewed in the January 2012 issue of Nature, the world’s most respected science journal. Nature appointed Caleb Scharf, an astrobiologist at Columbia University, to review Krauss’s book. Here is what he had to say on our subject:
He [Kraus] notes that a number of vital empirical discoveries are, ominously, missing from our cosmic model. Dark matter is one. Despite decades of astrophysical evidence for its presence, and plausible options for its origins, physicists still cannot say much about it. We don’t know what this major mass component of the Universe is, which is a bit of a predicament. We even have difficulty accounting for every speck of normal matter in our local Universe.
It is important to appreciate that dark matter is not something that was initially discovered in a laboratory, and whose existence was then used to explain some phenomenon. It is also not an entity whose existence was implied by some cosmological theory, and then applied to the problem of energetic stars. Dark matter is entirely hypothetical. Its existence was postulated to explain how the stars in spiral galaxies can orbit at such breakneck speeds without being flung off into the void. In other words, when astronomers tallied up all the mass in the universe, they came face to face with a phenomenon which they could not explain using known physical laws: those laws would indicate that stars in spiral galaxies should indeed be flying off in all directions. Since they aren’t, there must be something out there to prevent them from doing so. What that something is remains anybody’s guess, as Professor Kaler pointed out above.
Recently, TIME Magazine reported on an effort to elucidate the nature of dark matter. The TIME writer begins by pointing out that “Together, [dark matter and dark energy] make up a whopping 96 percent of the cosmos—but to this day, nobody can say with any confidence what either one of them actually is.”
TIME reports on a planned 2020 space mission named Euclid that will try to “sniff out the nature of these similarly named but (presumably) unrelated phenomena.” It then offers a bit of history. “The mystery of dark matter goes all the way back to the 1930s, when Caltech astronomer Fritz Zwicky noted that some galaxies seemed to be orbiting each other so fast that they should be slowly separating—each galaxy remaining discrete and intact, but the distances among them opening wider and wider. In the 1960s, the Carnegie Institution’s Vera Rubin and others realized that something similar ought to be true within individual galaxies—that they were whirling so fast they should rip themselves apart. And by the 1980s, astronomers were forced to accept the idea that the gravity from some mysterious, invisible form of matter had to be holding them all together.”
In Genesis and Genes, we also considered Dark Energy. I wrote
To complicate things further, throw in some dark energy. This is not techno-speak from a Star Wars film. It is a phenomenon, discovered in the late 1990s, which appears to cause the universe’s expansion to accelerate… The 2011 Nobel Prize in physics was awarded to a trio of astronomers for their discovery of this phenomenon. Adam Riess, Brian Schmidt and Saul Perlmutter were also acknowledged by the journal Science, which named their findings the Breakthrough of the Year in 1998. The problem is that nobody knows what this force could be. According to cosmologist Michael Turner of the University of Chicago, quoted in the January 2006 issue of New Scientist, “Cosmic acceleration is the biggest mystery in all of science.”
I pointed out what seems to be an obvious point:
Needless to say, if there is a force which is accelerating the universe’s expansion, and especially if its strength is varying, attempts to estimate the expansion of the universe in the past – and thus to infer its age – are enormously complicated. It may well be impossible to do so. Professor Kaler again: “But we have even less of an idea where this [dark] energy comes from than we do about the nature of dark matter. So to dark matter, add dark energy. Either that or something is terribly amiss with our concept of gravity.”
Here is what the recent TIME report had to say on the subject:
Dark energy is something entirely different—indeed, in some ways it’s the exact opposite: it’s a still-unknown force, discovered in the 1990s, that makes the universe expand faster and faster all the time. (Einstein originally came up with this idea, but eventually abandoned it). You can think of dark energy as a type of antigravity, but exactly what type — whether it fluctuates in strength over time, for example — is yet to be determined.
Finally, TIME tells us about what the new research program is meant to accomplish:
Euclid will tackle this problem as well, by looking at the distances among tens of millions of galaxies at many different stages of cosmic history—with objects more distant from Earth representing images that come to us from earlier in time. Using measurements of the primordial light left over from the Big Bang, theorists can predict how those distances should change as the universe evolves, both with and without dark energy in its various possible forms. By comparing the theories with what Euclid actually sees, they’ll be able to get a handle on which theory matches what’s happening in the cosmos.
There is a lot for informed consumers of science to chew on here. Let’s begin with the last paragraph above. It gives a hint of something that most members of the public are unaware of – that cosmology is mostly about theory. Of course, it starts with various observations, but then there is a wallop of theory, inference, statistical analyses and more. One should be parsimonious when using the word proof in the context of cosmology.
TIME refers to dark energy as a “still-unknown force”. Readers of Genesis and Genes will recall what I wrote about Peter Tait, one of the leading physicists of the late 19th century and a colleague of Lord Kelvin:
Tait’s lectures were based entirely on Kelvin’s arguments. He examined each in turn and admitted that the results drawn from them depended upon the twin assumptions that science knew all of the physical laws now in operation and that these laws have remained unchanged since the Earth was formed. He saw no reason to doubt either assumption.
The arguments advanced by Kelvin and Tait turned out to be wrong largely because they were unaware of radioactivity, a phenomenon unknown to science until the end of the 19th century. I made the point in Genesis and Genes that neither Tait nor Kelvin displayed even basic prudence about their calculations. For example, Tait, writing in the North British Review in 1869 asserted that “there was not the slightest possibility of error” in extrapolating back to the beginnings of the Earth and Sun on the basis of their thermal loss [and thus calculating their age to be, at most, 25 million years].
Dark matter and dark energy should give pause to those who accept uncritically all the absolutist statements about cosmology and cosmogony that emanate from PBS, National Geographic, Carl Sagan-wannabes and the general media. If we don’t know what 96% of the universe is made of, is it not a little premature to state the universe’s age, complete with a decimal point – 13.7 billion years?
Is it only religious fundamentalists/fanatics/obscurantists/biblical literalists who should harbour scepticism about claims that have to do with the ancient past?
 Caleb Scharf, Cosmology: Plucked from the vacuum. Nature 481 (26 January 2012), page 440. doi:10.1038/481440a.
Retrieved 4th March 2013.
This report is also interesting: