Posts Tagged ‘dark energy’

By Jeffrey Bennett

It has been exactly 100 years since Albert Einstein presented his theory of general relativity to an audience of scientists on November 25, 1915. While virtually everyone has heard of Einstein and his theory, very few people have any idea of what the theory actually is.

This is a shame, not only because there is a great public thirst for understanding of it, but also because relativity is important, for at least four major reasons.

General relativity provides our modern understanding of space, time and gravity — which means it’s crucial to almost everything we do in physics and astronomy. For example, you cannot understand black holes, the expansion of the universe or the Big Bang without first understanding the basic ideas of relativity. Though few people realize it, Einstein’s famous equation E = mc2 is actually part of the theory of relativity, which means that relativity also explains how the sun shines and how nuclear power works.

A second reason everyone should know about relativity lies in the way it changes our perception of reality. Relativity tells us that our ordinary perceptions of time and space are not universally valid. Instead, space and time are intertwined as four-dimensional space-time.

In our ordinary lives, we perceive only three dimensions—length, width and depth—and we assume that this perception reflects reality. However, in space-time, the four directions of possible motion are length, width, depth and time. (Note that time is not “the” fourth dimension; it is simply one of the four.)

Although we cannot picture all four dimensions of space-time at once, we can imagine what things would look like if we could. In addition to the three spatial dimensions of space-time that we ordinarily see, every object would be stretched out through time. Objects that we see as three-dimensional in our ordinary lives would appear as four-dimensional objects in space-time. If we could see in four dimensions, we could look through time just as easily as we look to our left or right. If we looked at a person, we could see every event in that person’s life. If we wondered what really happened during some historical event, we’d simply look to find the answer.

To see why this is so revolutionary, imagine that you met someone today who deeply believed that Earth is the center of the universe. You would probably feel sorry for this person, knowing that his or her entire world view is based on an idea disproven more than 400 years ago.

Now imagine that you met someone who still believed that time and space are independent and absolute — which, of course, describes almost everyone — even though we’ve known that’s not the case for a century now. Shouldn’t we feel equally sorry for all who hold this modern misconception?

It seems especially unfortunate once you realize that the ideas of relativity are not particularly difficult to understand. Indeed, I believe we could begin teaching relativity in elementary school in much the same way that we teach young children about the existence of atoms, even though few will ever study quantum mechanics.

My third reason for believing relativity is important lies in what Einstein’s discovery tells us about human potential. The science of relativity may seem disconnected from most other human endeavors, but I believe Einstein himself proved otherwise. Throughout his life, Einstein argued eloquently for human rights, human dignity and a world of peace and shared prosperity. His belief in underlying human goodness is all the more striking when you consider that he lived through both World Wars, that he was driven out of Germany by the rise of the Nazis, that he witnessed the Holocaust that wiped out more than six million of his fellow Jews, and that he saw his own discoveries put to use in atomic bombs.

No one can say for sure how he maintained his optimism in the face of such tragedies, but I see a connection to his discovery of relativity. Einstein surely recognized that a theory that so challenged our perceptions of reality might have been dismissed out of hand at other times in history, but that we now live in a time when, thanks to the process that we call science, the abundant evidence for relativity allowed for its acceptance.

This willingness to make judgments based on evidence shows that we are growing up as a species. We have not yet reached the point where we always show the same willingness in all our other endeavors, but the fact that we’ve done it for science suggests we have the potential.

Finally, on a philosophical level, relativity is profound. Only about a month before his death in 1955, Einstein wrote: “Death signifies nothing … the distinction between past, present and future is only a stubbornly persistent illusion.” As this suggests, relativity raises interesting questions about what the passage of time really means.

Because these are philosophical questions, they do not have definitive answers, and you will have to decide for yourself what these questions mean to you. But I believe that one thing is clear. Einstein showed that even though space and time can independently differ for different observers, the four-dimensional space-time reality is the same for everyone.

This implies that events in space-time have a permanence to them that cannot be taken away. Once an event occurs, in essence it becomes part of the fabric of our universe. Every human life is a series of events, and this means that when we put them all together, each of us is creating our own, indelible mark on the universe. Perhaps if everyone understood that, we might all be a little more careful to make sure that the mark we leave is one that we are proud of.

So there you have it. Relativity is necessary to comprehend the universe as we know it, it helps us understand the potential we all share when we put our brains to work for the common good, and if we all understood it we might treat each other a little more kindly.


Take a look around you, and in your mind’s eye, randomly wipe out all but a small fraction of what you can see. Pretend the vast rest of reality is there but invisible.

You’d probably like a device that helps you see much more of it.

Scientists working at CERN, the European Organization for Nuclear Research, have made some progress in that direction with the Alpha Magnetic Spectrometer (AMS), which has been riding aboard the International Space Station since 2011.

Physicists believe that mental exercise in blindness reflects the reality of our universe, only about 4% of which manifests as the kind of matter and energy we can perceive.

More than 70% consists of so-called dark energy, physicists say, and more than 20% is dark matter, neither of which humans can directly detect so far.

But scientists feel certain it must exist, partly because of the gravity it exerts on the visible universe.

This week, CERN scientists published an analysis of data from the AMS, which detects subatomic particles constantly bombarding Earth. They include exceedingly rare antimatter particles that can result from the breakdown of dark matter.
They are called positrons, also known as anti-electrons. They have the same mass as electrons, but electrons have a negative charge, and positrons have a positive charge.

Scientists believe dark matter collides, splitting into pairs of electrons and positrons, so the ability to examine positrons in detail could help in proving the existence of dark matter.

Positrons are produced in minute quantities in our corner of the universe, and mostly come flying our way from its far reaches, bundled up with gangs of other subatomic particles, mainly protons and electrons.

The flying particles bear the name “cosmic rays,” a misnomer given to them at a time when they were not as well understood.

The AMS project has analyzed 41 billion cosmic ray particles, and determined 10 million of them to be made of electrons and positrons.
There have been fluctuations in the number of positrons in the mix, and thanks to the orbiting spectrometer, for the first time in a half-century of cosmic ray research scientists have been able to measure an important peak in positrons.

“AMS now unveiled data that no other experiment could ever record,” said CERN spokesman Arnaud Marsollier.

The data hint at the existence of dark matter. But CERN scientists are not completely sure yet that dark matter is the true source of the positrons.

“It may come from high-energy phenomena somewhere in our universe: But what?” Marsollier asks. “Pulsars? Supernovas?”

Pulsars are stars similar to black holes that spray particles and light through the universe. Supernovas are exploded former stars.

Because it detects particles as opposed to light, the way a telescope would, AMS may also be able to see other cosmic phenomena a telescope cannot.

The data released this week need more study, but at first glance, CERN says, what they have seen so far looks “tantalizingly consistent with dark matter particles.”

If that’s the case, the AMS may have begun to remove humanity’s greatest blindfold.