Have you ever wondered why we age and grow old?
In the movie “The Curious Case of Benjamin Button,” Brad Pitt springs into being as an elderly man and ages in reverse.
To the bafflement of scientists, the fundamental laws of physics have no preference for a direction in time, and work just as well for events going forward or going backward in time. Yet, in the real world, coffee cools and cars break down. No matter how many times you look in the mirror, you’ll never see yourself grow younger. But if the laws of physics are symmetric with respect to time, then why do we experience reality with the arrow of time strictly directed from the past to the future?
A new paper just published in Annalen der Physik — which published Albert Einstein’s theories of special and general relativity — Dmitry Podolsky, a theoretical physicist now working on aging at Harvard University, and I explain how the arrow of time ‒ indeed time itself ‒ is directly related to the nature of the observer (that is, us).
Our paper shows that time doesn’t just exist “out there” ticking away from past to future, but rather is an emergent property that depends on the observer’s ability to preserve information about experienced events. Read More
Many of the questions I am asked regard how “true” science fiction concerning black holes might be, and whether worm holes, such as those featured in Stargate, are real or not. Invariably though, the one item that is almost assured to come up are the largely gruesome ways in which black holes might theoretically affect human beings and the Earth itself.
There are three properties of a black hole that are (in principle) measurable: their mass, their spin (or angular momentum) and their overall electronic charge. Indeed, these are the only three parameters that an outside observer can ever know about since all other information about anything that goes into making up a black hole is lost. This is known as the “no hair theorem”. Put simply: no matter how hairy or complex an object you throw into a black hole, it will get reduced down (or shaved) to its mass, charge and spin.
Of these parameters, mass is arguably the most significant. The very definition of a black hole is that it has its mass concentrated in to a vanishingly small volume – the “singularity”. And it is the mass of the black hole – and the huge gravitational forces that its mass generates – which does the “damage” to nearby objects.
One of the best known effects of a nearby black hole has the imaginative title of “Spaghettification”. In brief, if you stray too close to a black hole, then you will stretch out, just like spaghetti.
This effect is caused due to a gravitation gradient across your body. Imagine that you are headed feet first towards a black hole. Since your feet are physically closer to the black hole, they will feel a stronger gravitation pull toward it than your head will. Worse than that, your arms, by virtue of the fact that they’re not at the center of your body, will be attracted in a slightly different (vector) direction than your head is. This will cause parts of the body toward the edges to be brought inward. The net result is not only an elongation of the body overall, but also a thinning out (or compression) in the middle. Hence, your body or any other object, such as Earth, will start to resemble spaghetti long before it hits the center of the black hole.
The exact point at which these forces become too much to bear will depend critically on the mass of a black hole. For an “ordinary” black hole that has been produced by the collapse of a high mass star, this could be several hundred kilometers away from the event horizon – the point beyond which no information can escape a black hole. Yet for a supermassive black hole, such as the one thought to reside at the center of our galaxy, an object could readily sink below the event horizon before becoming spaghetti, at a distance of many tens of thousands of kilometers from its center. For a distant observer outside the event horizon of the black hole, it would appear that we progressively slow down and then fade away over time.
What would happen, hypothetically, if a black hole appeared out of nowhere next to Earth? The same gravitational effects that produced spaghettification would start to take effect here. The edge of the Earth closest to the black hole would feel a much stronger force than the far side. As such, the doom of the entire planet would be at hand. We would be pulled apart.
Equally, we might not even notice if a truly supermassive black hole swallowed us below its event horizon as everything would appear as it once was, at least for a small period of time. In this case, it could be some time before disaster struck. But don’t lose too much sleep, we’d have to be unfortunate to “hit” a black hole in the first place – and we might live on holographically after the crunch anyway.
Interestingly, black holes are not necessarily black. Quasars – objects at the hearts of distant galaxies powered by black holes – are supremely bright. They can readily outshine the rest of their host galaxy combined. Such radiation is generated when the black hole is feasting on new material. To be clear: this material is still outside the event horizon which is why we can still see it. Below the event horizon is where nothing, not even light, can escape. As all the matter piles up from the feast, it will glow. It is this glow that is seen when observers look at quasars.
But this is a problem for anything orbiting (or near) a black hole, as it is very hot indeed. Long before we would be spaghettified, the sheer power of this radiation would fry us.
For those who have watched Christopher Nolan’s film Interstellar, the prospect of a planet orbiting around a black hole might be an appealing one. For life to thrive, there needs to be a source of energy or a temperature difference. And a black hole can be that source. There’s a catch, though. The black hole needs to have stopped feasting on any material – or it will be emitting too much radiation to support life on any neighboring worlds.
What life would look like on such a world (assuming its not too close to get spaghettified, of course) is another matter. The amount of power received by the planet would probably be tiny compared to what Earth receives from the Sun. And the overall environment of such a planet could be equally bizarre. Indeed, in the creation of Interstellar, Kip Thorne was consulted to ensure the accuracy of the depiction of the black hole featured. These factors do not preclude life, it just makes it a tough prospect and very hard to predict what forms it could take.
Nearly a century ago, Edwin Hubble’s discovery of red-shifting of light from galaxies in all directions from our own suggested that space itself was getting bigger. Combined with insights from a handful of proposed non-Euclidean geometries, Hubble’s discovery implied that the cosmos exists in more than the three dimensions we’re familiar with in everyday life.
That’s because parts of the cosmos were moving further apart, yet with no physical center, no origin point in three-dimensional space. Just think of an inflating balloon seen only from the perspective of its growing two-dimensional surface, and extrapolate to four-dimensional inflation perceived in the three-dimensional space that we can see. That perspective suggests that three-dimensional space could be curved, folded, or warped into a 4th dimension the way that the two dimensional surface of a balloon is warped into a 3rd dimension.
We don’t see or feel more dimensions; nevertheless, theoretical physics predicts that they should exist. Interesting, but are there any practical implications? Can they become part of applied physics?
In 1971—16 years after Einstein’s death—the definitive experiment to test Einstein’s relativity was finally carried out. It required not a rocket launch but eight round-the-world plane tickets that cost the United States Naval Observatory, funded by taxpayers, a total of $7,600.
The brainchild of Joseph Hafele (Washington University in St. Louis) and Richard Keating (United States Naval Observatory) were “Mr. Clocks,” passengers on four round-the-world flights. (Since the Mr. Clocks were quite large, they were required to purchase two tickets per flight. The accompanying humans, however, took up only one seat each as they sat next to their attention-getting companions.)
The Mr. Clocks had all been synchronized with the atomic clock standards at the Naval Observatory before flight. They were, in effect, the “twins” (or quadruplets, in this case) from Einstein’s famous twin paradox, wherein one twin leaves Earth and travels nearly at the speed of light. Upon returning home, the traveling twin finds that she is much younger than her earthbound counterpart.
In fact, a twin traveling at 80 percent the speed of light on a round-trip journey to the Sun’s nearest stellar neighbor, Proxima Centauri, would arrive home fully four years younger than her sister. Although it was impossible to make the Mr. Clocks travel at any decent percentage of the speed of light for such a long time, physicists could get them going at jet speeds—about 300 meters (0.2 mile) per second, or a millionth the speed of light—for a couple of days. In addition, they could get the Mr. Clocks out of Earth’s gravitational pit by about ten kilometers (six miles) relative to sea level. And with the accuracy that the Mr. Clocks were known to be capable of, the time differences should be easy to measure.
Science has done it again everybody! Brace yourselves for this groundbreaking news, freshly determined by physicists: Time travel, if it exists, may have some weird consequences. Gosh, who’d have thunk it?
But no, seriously, a recent article suggests that a certain kind of theoretically possible time machine would wreak minor havoc with a firm principle of quantum mechanics, the often-weird science of the smallest bits of the universe. You know what this means: We get to explore the science of time travel!
Let’s get this out of the way first: Obviously time travel exists, because it’s already the third week of 2014. We’re all time travelers (chrononauts), technically, moving 1 second per second through time. Certain weird side effects of relativity theory also mean time can travel more quickly under certain conditions, so it’s even possible for you to travel into the future (someone else’s future, at least) faster than the usual rate.
The “useful” kind of time travel, though, for sci-fi authors and dreamers alike, is into the past, Back to the Future style. And, happily, relativity theoretically can make that possible, too, by warping the fabric of reality, space-time, so much that it loops back on itself. A so-called wormhole (again, officially deemed possible by science) could be the bridge that connects two different times.
Andrew Grant is an associate editor at DISCOVER. His latest feature, “William Borucki: Planet Hunter,” appears in the December issue of the magazine.
Last night Major League Baseball announced the winners of the Cy Young Award, given to the year’s best pitchers in the American and National leagues. The National League victor was New York Mets pitcher R.A. Dickey. That he won the award is remarkable, and not just because he is a relatively ancient 38 years old or because he plays for the perennial punch line Mets. Dickey is the first Cy Young winner whose repertoire consists primarily of the knuckleball, a baffling pitch whose intricacies scientists are only now beginning to understand.
Most pitchers, including the other Cy Young finalists, try to overwhelm hitters with a combination of speed and movement. They throw the ball hard—the average major league fastball zooms in at around 91 miles per hour—and generate spin (up to 50 rotations a second) that makes the ball break, or deviate from a straight-line trajectory. Dickey does neither of those things. Rather than cock his arm back and fire, he pushes the ball like a dart so that it floats toward the plate between 55 and 80 mph. The ball barely spins at all—perhaps a quarter- or half-turn before reaching the hitter.
In 1917, a year after his general theory of relativity was published, Einstein tried to extend his field equation of gravitation to the universe as a whole. The universe as known at the time was simply our galaxy—the neighboring Andromeda, visible to the naked eye from very dark locations, was thought to be a nebula within our own Milky Way home. Einstein’s equation told him that the universe was expanding, but astronomers assured him otherwise (even today, no expansion is evident within the 2-million-light-year range to Andromeda; in fact, that galaxy is moving toward us). So Einstein inserted into his equation a constant now known as “lambda,” for the Greek letter that denoted it. Lambda, also called “the cosmological constant,” supplied a kind of force to hold the universe from expanding and keep it stable within its range. Then in 1929, Hubble, Humason, and Slipher made their monumental discovery using the 100-inch Mount Wilson telescope in California of very distant galaxies and the fact that they were receding from us—implying that the universe was indeed expanding, just as Einstein’s original equation had indicated! When Einstein visited California some time later, Hubble showed him his findings and Einstein famously exclaimed “Then away with the cosmological constant!” and never mentioned it again, considering lambda his greatest “blunder”—it had, after all, prevented him from theoretically predicting the expansion of the universe.
Fast forward six decades to the 1990s. Saul Perlmutter, a young astrophysicist at the Lawrence Berkeley Laboratory in California had a brilliant idea. He knew that Hubble’s results were derived using the Doppler shift in light. Light from a galaxy that is receding from us is shifted to the red end of the visible spectrum, while a galaxy that is approaching us has its light shifted to the blue end of the spectrum, from our vantage point. The degree of the shift is measured by a quantity astronomers call Z, which is then used to determines a galaxy’s speed of recession away from us (when Z is positive and shift is to the red).