Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe

by Lisa Randall

Although we might experience the illusion of a self-contained environment, every day at sunrise and every night when the Moon and the far more distant stars come into view, we are reminded that our planet is not alone.

Dark matter constitutes 85 percent of the matter in the Universe while ordinary matter—such as that contained in stars, gas, and people—constitutes only 15 percent.

Ten times more bacterial cells than human cells live inside us and help with our survival.

Dark matter is not made out of the same material as ordinary matter—it’s not composed of atoms or the familiar elementary particles that do interact with light, which is essential to everything we can see.

Scientists have studied many forms of matter but all of them whose composition we know have been observed with some form of light—or more generally, electromagnetic radiation.

It would be even more mysterious to me if the matter we can see with our eyes is all the matter that exists.

The big lesson of physics over the centuries is how much is hidden from our view.

Dark matter is not dark—it is transparent. Dark stuff absorbs light. Transparent things, on the other hand, are oblivious to it. Light can hit dark matter, but neither the matter nor the light will change as a result.

Dark energy is not matter—it is just energy. Dark energy exists even if no actual particle or other form of stuff is around. It permeates the Universe, but doesn’t clump like ordinary matter. The density of dark energy is the same everywhere—it can be no denser in one region than another.

Dark energy also remains constant over time. Unlike matter or radiation, dark energy does not become more dilute when the Universe expands. This is in some respects its defining property. The dark energy density—energy not carried by particles or matter—remains the same over time. For this reason, physicists often refer to this type of energy as a cosmological constant.

That is, stars rotated with constant velocity, even well beyond the region containing luminous matter.

Either the Universe was around an infinite length of time or it started at some particular time.

meteor showers are more regular occurrences that arise from the Earth passing through comet debris.

Planetary scientists call those elements with melting point below 100 degrees kelvin gases—independent of the actual phase the matter is in. Those with low melting point, but not so low as gases, are referred to—again by planetary scientists—as ices, though whether or not the material is actually an ice also depends on the actual temperature. That is why Jupiter and Saturn are called gas giants, while Uranus and Neptune are sometimes called ice giants. In both cases, the interior is actually a hot, dense fluid.

In fact comet surfaces seem to be the darkest ones in the Solar System.

The favored response to changing conditions is most often migration to a new location with a more suitable environment—but of course only if such an environment is accessible. When a species can’t adapt or relocate to a suitable habitat, it doesn’t stand a chance.

About half a billion years later began the “boring billion,” in which no other radical development took place—at least that we know of.

thought the Earth changed only through tiny alterations that nevertheless yielded major effects over long periods of time.

In another four billion years or so, the Sun will turn into a red giant, and a few billion years after that, it will burn out completely. According to current models, no forms of Earth-bound life—simple or complex—will survive in that distant future.

The best science should always encompass, or at the very least be consistent with, the broadest possible range of observations.

The orbits of a few of these icy bodies became so distorted that their paths took them to the inner Solar System, where some broke away from their initial trajectories under gravity’s distorting effect. At least one of these icy bodies might have turned into a comet on a collision course with the Earth.