Earlier this year, Dr. Sabine Hossenfelder, a theoretical physicist in Stockholm, made the jarring suggestion that dark matter might cause cancer. She was not talking about the “dark matter”Dark Matter of the genome (another term for junk DNA) but about the hypothetical, lightless particles that cosmologists believe pervade the universe and hold the galaxies together.
Though it has yet to be directly detected, dark matter is presumed to exist because we can see the effects of its gravity. As its invisible particles pass through our bodies, they could be mutating DNA, the theory goes, adding at an extremely low level to the overall rate of cancer.
It was unsettling to see two such seemingly different realms, cosmology and oncology, suddenly juxtaposed. But that was just the beginning. Shortly after Dr. Hossenfelder broached her idea in an online essay,
Michael Rampino, a professor at New York University, added geology and paleontology to the picture.
WHAT IS DARK MATTER?
Dark matter makes up 85% of the universe, and is invisible because it does not reflect light.
It can’t be seen directly with telescopes but astronomers know it exists because of the gravitational effects it has on matter we see.
The European Space Agency said: ‘Shine a torch in a completely dark room, and you will see only what the torch illuminates. ‘That does not mean that the room around you does not exist. ‘Similarly we know dark matter exists but have never observed it directly.’
Scientists are fairly sure it exists and is crucial to the universe, but they do not know what it looks like or where to find it.
Dark matter is thought to be the gravitational ‘glue’ that holds the galaxies together, while just 5 per cent the universe consists of known material like atoms and subatomic particles.
His idea is based on speculations by other scientists that the Milky Way is sliced horizontally through its centre by a thin disk of dark matter. As the sun, traveling around the galaxy, bobs up and down through this darkling plane, it generates gravitational ripples strong enough to dislodge distant comets from their orbits, sending them hurtling toward Earth.
An earlier version of this hypothesis was put forth last year by the Harvard physicists Lisa Randall and Matthew Reece. But Dr. Rampino has added another twist: During Earth’s galactic voyage, dark matter accumulates in its core. There the particles self-destruct, generating enough heat to cause deadly volcanic eruptions. Struck from above and below, the dinosaurs succumbed.http://arxiv.org/abs/1403.0576
It is surprising to see something as abstract as dark matter take on so much solidity, at least in the human mind. The idea was invented in the early 1930s as a theoretical contrivance — a means of explaining observations that otherwise didn’t make sense.
Galaxies appear to be rotating so fast that they should have spun apart long ago, throwing off stars like sparks from a Fourth of July pinwheel. There just isn’t enough gravity to hold a galaxy together, unless you assume that it hides a huge amount of unseen matter — particles that neither emit or absorb light.
Image: File:Green pinwheel.jpg
Some mavericks(someone who exhibits great independence in thought and action) propose alternatives, attempting to tweak the equations of gravity to account for what seems like missing mass. But for most cosmologists, the idea of unseeable matter has become so deeply ingrained that it has become almost impossible to do without it.
THE COSMIC MICROWAVE BACKGROUND RADIATION – LOOKING BACK IN TIME
Much of what scientists know about the relative contributions of dark matter and dark energy comes from the relic radiation left behind from the Big Bang, called the cosmic microwave background (CMB).
We can measure the CMB by looking far into the distant universe.
Information can only travel at the speed of light, meaning that if we look far enough away we can see events that happened in the past.
Looking at the sun, you see it as it was eight minutes ago because the light takes eight minutes to reach us.
In a sense the CMB is a glimpse into the very start of our universe.
Said to be five times more abundant than the stuff we can see, dark matter is a crucial component of the theory behind gravitational lensing, in which large masses like galaxies can bend light beams and cause stars to appear in unexpected parts of the sky.
That was the explanation for the spectacular observation of an “Einstein Cross” reported last month. Acting like an enormous lens, a cluster of galaxies deflected the light of a supernova into four images — a cosmological mirage. The light for each reflection followed a different path, providing glimpses of four different moments of the explosion.
But not even a galactic cluster exerts enough gravity to bend light so severely unless you postulate that most of its mass consists of hypothetical dark matter. In fact, astronomers are so sure that dark matter exists that they have embraced gravitational lensing as a tool to map its extent.
Dark matter, in other words, is used to explain gravitational lensing, and gravitational lensing is taken as more evidence for dark matter.
WHAT IS A BOSE-EINSTEIN CONDENSATE?
Physicists know that when quantum particles condense, they lose their individuality.Their different energy levels collapse into a single macroscopic quantum state, causing them to behave like clones and form a ‘super particle’ or wave known as a Bose-Einstein condensate (BEC) In 1995 scientists made a BEC when they cooled a cloud of rubidium and sodium atoms to within a few billionths of a degree above absolute zero. The first BEC had unique properties which will help scientists probe the basic behaviour of matter. The achievement earned the researchers a Nobel Prize.
Some skeptics have wondered if this is a modern-day version of what ancient astronomers called “saving the phenomena.” With enough elaborations, a theory can account for what we see without necessarily describing reality. The classic example is the geocentric model of the heavens that Ptolemy laid out in the Almagest, with the planets orbiting Earth along paths of complex curlicues.
THE THEORY OF RELATIVITY
In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers – known as the theory of special relativity. This groundbreaking work introduced a new framework for all of physics, and proposed new concepts of space and time. He then spent 10 years trying to include acceleration in the theory, finally publishing his theory of general relativity in 1915. This determined that massive objects cause a distortion in space-time, which is felt as gravity. At its simplest, it can be thought of as a giant rubber sheet with a bowling ball in the centre. As the ball warps the sheet, a planet bends the fabric of space-time, creating the force that we feel as gravity. Any object that comes near to the body falls towards it because of the effect. Einstein predicted if two massive bodies came together it would create such a huge ripple in space time that it should be detectable on Earth.
Ptolemy apparently didn’t care whether his filigrees were real. What was important to him was that his model worked, predicting planetary movements with great precision.
Modern scientists are not ready to settle for such subterfuge. To show that dark matter resides in the world and not just in their equations, they are trying to detect it directly.
Though its identity remains unknown, most theorists are betting that dark matter consists of WIMPs — weakly interacting massive particles. If they really exist, it might be possible to glimpse them when they interact with ordinary matter.
Based on that hope, scientists have constructed underground detectors attempting to measure the impact of the particles as they fly through Earth and occasionally collide with atoms of xenon, argon or some other substance. But so far, there have been no hits.
WHAT ARE GRAVITATIONAL WAVES?
The universe is made up of a ‘fabric of space-time’. This corresponds to Einstein’s General Theory of Relativity, published in 1916. Objects in the universe bend this fabric, and more massive objects bend it more. Gravitational waves are considered ripples in this fabric. They can be produced, for instance, when black holes orbit each other or by the merging of galaxies. It was the merging of two black holes that produced the gravitational waves detected in February. Gravitational waves are also thought to have been produced when the universe went through a period of inflation, not long after the Big Bang.
Somewhere from 10 to a few thousand times a year, Dr. Hossenfelder estimated, a WIMP may happen to strike one of our own atoms, including some that make up DNA. The energy would be strong enough to break molecular bonds and cause mutations.
Simulation of gravitational waves generated by black hole merger http://www.dailymail.co.uk/video/sciencetech/video-1177629/Simulation-gravitational-waves-generated-black-hole-merger.html
When it comes to cancer, that is a negligible threat. Two of Dr. Hossenfelder’s colleagues, Katherine Freese and Christopher Savage, estimate that cosmic rays zipping through a human body cause more damage in a second than dark matter would in a lifetime. But the effect of dark matter is still strong enough that scientists are considering using DNA or RNA molecules as WIMP detectors.
If WIMPs turn out to be a fiction, something else will have to be found to explain all of the missing mass. Something is screwy about the universe, and astronomers are determined to find out why.
A version of this article appears in print on April 21, 2015, on page D4 of the New York edition with the headline: Dark Matter’s Deep Reach.