The 4% Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality

by Richard Panek

Whereas Newton imagined gravity as a force that acts across space, Einstein’s equations cast gravity as a property that belongs to space. In Newton’s physics, space was passive, a vessel for a mysterious force between masses. In Einstein’s physics, space was active, collaborating with matter to produce what we perceive as gravity’s effects. The Princeton physicist John Archibald Wheeler offered possibly the pithiest description of this co-dependence: “Matter tells space how to curve. Space tells matter how to move.”

thinking. Like cultures that count “One, two, three, more,” we tend to regard the scale of the universe—to the

Consider: How long would it take you to count to a million at the “one Mississippi” rate of one second per number? Eleven days—or, to be exact, 11 days, 13 hours, 46 minutes, and 40 seconds. How long would it take you to count to a billion at the same rate? A billion is a thousand million—that is, a million one thousand times over. So you would have to count a million Mississippis—eleven days of counting—a thousand times. That’s 31 years, 8% months. To reach a trillion, you’d have to count to a billion a thousand times—31 years a thousand times, or 31,000 years.

findings, Jim Peebles

Astrophysical Journal, in November 1965, the Princeton and Bell Labs articles had appeared in print,

slapdash,”

Jeremiah

Scientists had known since the nineteenth century that if you rotated an initially spherical liquid drop it would become oblate, increasingly so, and eventually compress into a bar shape.

He could see at a glance that it should have become bar-shaped or broken up into two galaxies after one rotation. Yet by now the Milky Way was old enough to have completed a dozen rotations.

Fritz Zwicky,

Sinclair Smith

“that a further analysis of the problem is in order.”

neophyte

Galaxies were living fast but not dying young.

“After reviewing all the evidence, it is our opinion that the case for invisible mass in the Universe is very strong and getting stronger.”

“Nobody ever told us that all matter radiated,” Vera Rubin liked to say. “We just assumed that it did.”

Babel or emulating Icarus,

hubris

Saul Perl...

Carl Pennypacker

syllogism

equation—the Greek symbol lambda, “at present unknown”—to represent whatever it was that was keeping the universe from collapsing.

The reason the universe wasn’t collapsing of its own weight was that it was expanding.

scion

Jim Peebles’s book Physical Cosmology, and

Perlmutter

Before science was science (the study of nature through close observation), it was philosophy (the study of nature through deep thought).

Nemesis.

recesses

Perlmutter and Pennypacker

Perlmutter

Now that, Schmidt thought, is the mark of a good problem in science. It’s not when people say, “Oh, that’s interesting.” It’s when they say, “Ooo, can I be part of that?”

The other type—the type that Zwicky observed—begins life as a hydrogen-rich star like our own Sun. As it ages, the Sun will shed its outer hydrogen layer while its core contracts under gravitational pressure. In the end, only the core will remain—a shrunken skull called a white dwarf, with the mass of the Sun packed into the volume of Earth. If a white dwarf had a companion star (and most stars in our galaxy do), then at this point it might start to siphon gas off the other star. In the 1930s, the Indian mathematician Subrahmanyan Chandrasekhar calculated that when a star of this kind reaches a certain size—1.4 times the mass of the Sun, or the Chandrasekhar limit—it will begin to collapse of its own weight.

Suntzeff loved historical connections in astronomy. A great-uncle of his had gone to school in Russia with Otto Struve, the descendant of a line of

Struve fled Russia and the Bolsheviks at the time of the revolution and wound up in Turkey, impoverished, until a relative put him in touch with the director of the Yerkes Observatory in Wisconsin, who offered him a job as a spectroscopist. Struve later became director of the observatory, as well as McDonald Observatory in Texas and Leuschner Observatory in Berkeley. Suntzeffs family also fled Russia, though they headed in the other direction, to China and, eventually, San Francisco. There Suntzeffs grandmother reunited with Otto Struve. Small world.

But now the charge-coupled device, or CCD, promised to do for the photographic plate what the photographic plate had done for the eyeball.

Mario Hamuy

Gustav Tammann.

Bob Kirshner

“You can check and recheck your results forever,” he said, “but at some point you’ve got to have the balls, basically, you’ve got to have the courage, to announce your result and to say, ‘Okay, here is an accounting of our uncertainties. This is where we stand.’”

NICMOS was particularly sensitive to distant objects whose light was so redshifted that, by the time it reached our patch of the universe, it had left the visible part of the electromagnetic spectrum.

If the differences in temperature were greatest between points separated by less than 1 degree, then the universe was open; by more than 1 degree, then the universe was closed; by 1 degree, then the universe was flat. So far, the verdict was all flat.

There: SN 1997ff. A gasp.

the protons and neutrons, collectively called baryons,

How do you do something that is, by your own definition, impossible to do?

You don’t. You rethink the question.

Save the appearances. Think. Theorize.

suffusing

Galaxies formed first, at redshifts of 2 to 4—or roughly nine to twelve billion years ago. Then those galaxies gathered into clusters, at redshifts of less than 1—or less than roughly six billion years ago. And now, today (in a cosmic sense), those clusters are gathering into superclusters. Matter clumped first in small structures, and those small structures continued to gather together. The universe has apparently had a bottom-up, simple-to-complex

complex history, consistent with theoretical cold-dark-matter models.