Home > Newsletter Archive > Newsletter #30
2. Gravity and Antigravity
Well, several people have written to me asking when the next newsletter will be going out so, without further procrastination, here it is. Since I last wrote, my latest book, Teleportation: the Impossible Leap, has been published and appears to have been, as they say, “well received.” Fingers crossed, then. Lots of e-mails have been coming in with questions about the science and practicility of beaming around and I’ve been on radio in the US and UK fielding questions about the book and its implications. Some of the imaginative ideas people have had will make great material for a second edition.
The possibility of human teleportation, of course, is what captivates everyone; just imagine being able to hop to anywhere on the planet (or maybe beyond) in the wink of an eye. Think of the convenience, the places you could go, just on the spur of the moment. Evening meal in Venice, home to bed, then a quick early morning jump to see sunrise at Machu Picchu. But there are concerns about what this amazing new technology might mean as well. While I was talking to George Noory on Coast-to-Coast radio last month, a trucker (driving his sixteen-wheeler through Texas at the time) called in to ask what the future might hold for people like him involved in conventional forms of transport. Who’d need trucks, trains, and planes when instant teleportation was available? On the other hand, with all the cars off the road, it would certainly the environment a much needed.
Other folk have queried the security aspects of the whole thing. With teleportation booths in every home, what would there be to stop thieves materializing in the dead of night and beaming out all your valuables? And if you think junk e-mail is a headache, wait till you see what those crazy marketing types can teleport into your living room every day! Howard Hughes, who interviewed me on the UK’s TalkSport radio, was worried about Julian Clary appearing in his flat at midnight a terrifying prospect indeed.
If you haven’t ordered your copy yet, Teleportation is available through any good bookstore (and probably a few bad ones as well), including on-line suppliers such as Amazon. (A link to the Amazon page is also on the front page of my website.)
At the moment, I’m putting the finishing touches to a new book that will be coming out next year. Called Gravity: the Story of a Force, it’s exactly that: the tale of how we’ve learned about gravitation from the ancient Greeks to the 21st century and all the mysteries we presently confront: the nature of dark matter and dark energy, the possibility of antigravity, and the problem of the Pioneer anomaly why two of our spacecraft aren’t quite where they should be.
2. Gravity and Antigravity
Gravity has a long and convoluted history. Aristotle gave it a lot of thought way back in the third century B.C. and pretty much decided the way people believed gravity worked until Galileo and Newton came along. According to Aristotle, gravity was something inside an object. Heavy things, like rocks, had a lot of gravity inside them; lighter objects, such as feathers, had less. Some substances, like fire, didn’t possess gravity at all but had “levity” instead, which made them rise. (We still use “gravity” and “levity” to mean serious or weighty on the one hand, and light-hearted on the other.)
Imagine how surprised Aristotle would have been to see that demonstration in August 1971 when David Scott, commander of the Apollo 15 mission, simultaneously dropped a hammer and a feather on the Moon. He’d have been shocked for three reasons: television would have seemed like a miracle, travel to the Moon oughtn't to have been possible by his reckoning (the Moon being part of the inaccessible heavens), and the hammer and feather hitting the surface at the same time simply shouldn‘t have happened in his scheme of gravity. Aristotle didn’t realize that some things fall more slowly on Earth because of air resistance. Take away the air and everything falls at exactly the same rate.
It took a couple of thousand years for people to cotton on to this. The breakthrough came when Galileo did a series of experiments in the early 1600s that involved rolling balls down inclined planes. By effectively diluting the force of gravity he could accurately measure the rate at which things fell and so figure out the math behind it. (The tale of him dropping things from the Leaning Tower of Pisa to show that they fell at the same rate makes a nice mental image but may never have actually happened.)
I just used the phrase “force of gravity” because, with Galileo and Newton, came the realization that gravity wasn’t so much inside things as an interaction between all objects that have mass. Newton figured out that gravity works everywhere the same, whether its on Earth or in the far reaches of outer space. That’s why his theory is called the universal law of gravitation. Using the math of Newton’s theory, astronomers were able to accurately work out the orbits of the planets and the paths of comets around the Sun. But there were still some nagging problems. How did Newtonian gravity this mysterious “action at a distance” work? How did objects, maybe millions of miles across the vacuum of space, “know” that others were there so that they could interact with them? Also, there was the issue of the speed of gravity. In Newton’s theory this is assumed to be infinite. But by what means could gravity act instantaneously?
Worse was to come for Newton’s theory. It gradually became clear that Mercury wasn’t moving around the Sun as Newton said it should. The rate at which its perihelion (it’s point of closest approach to the Sun) changed was a bit more 43 seconds of arc per century more than it was supposed to be. One possible explanation was that there was another planet closer to the Sun than Mercury that was upsetting Mercury’s motion. But lengthy searches for this hypothetical world, called Vulcan, drew a blank.
By the turn of the twentieth century, some scientists were beginning to realize there was something seriously wrong with our notions of space and time, and maybe of gravity too. Enter Einstein with his theory of relativity: first the special theory in 1905 and then the general theory in 1916. What the general theory amounted too was a completely new outlook on gravity. Gone was the idea of gravity as a force; instead gravity emerged purely as the result of the curvature of spacetime. Einstein was delighted when his new theory predicted exactly the measured discrepancy in Mercury’s and also the amount by which starlight is bent as it passes close to the Sun during a total eclipse.
But is general relativity the last word on gravity? Scientists know it can’t be for one very good reason: general relativity doesn’t mesh with quantum mechanics. Something is going to have to give if we’re to understand what happens to gravity on really tiny scales and regions where the curvature of spacetime is extreme (inside black holes, for example). So, the hunt is on for a theory of everything (TOE) in which gravity is factored in along with the other three forces of nature, electromagnetism and the strong and weak forces. The most popular candidate for this at present is superstring theory, or a version of it called M-theory. But more on this in a later newsletter.
There are other reasons, too, to question our current understanding of gravity. Anomalies have been reported by some scientists in how pendulums behave at the time of solar eclipses. This effect was first noticed by the Nobel Prize winner Maurice Allais in 1954 and has been named after him. A lot of researchers still doubt whether the Allais Effect is real, but there have been several corroborative studies using different instruments all suggesting that something peculiar is going on when the Sun, Moon and Earth are in a direct line. This “something” may or may not be related to another oddity that involves the two Pioneer spaceprobes that are presently heading out of the Solar System. Although both probes have now stopped transmitting, JPL mission specialists had spotted back in 1998 that there was an anomaly. Pioneer 10 and its sister craft Pioneer 11 were slightly off course (P10 now by about 400,000 km) and receding from the Sun just a tad more slowly than predicted. It was as if the Solar System were tugging on them just a bit harder than it should have done given its known content of matter.
Explanations for the Pioneer anomaly? There’s no shortage of them. Maybe the deviations from the planned trajectories have to do with the probes themselves, venting fuel or emitting heat radiation that’s pushing them differently than expected. But spacecraft engineers think they’ve eliminated these possibilities. So perhaps there’s something wrong with our understanding of gravity, inertia, or time. Another possibility that’s been suggested is that the Pioneer’s are being pulled off course by an unseen cloud of dark matter in the vicinity of the Solar System. There have been calls to send out another spacecraft specifically to study the unknown effect. But a cheaper way might be to look at the orbits of some asteroids that venture far from the Sun into the anomaly zone. For more on this idea, see this New Scientist article.
If there’s gravity can there also be antigravity? Gravity’s unusual in that we don’t normally see opposite kinds of it as we do in the case of electricity (positive and negative charges) and magnetism (north and south poles). Also, it’s difficult to see how antigravity would work in the general relativity scheme of things where gravity is a manifestation of the geometry of spacetime. And yet we now know that there is in fact a kind of antigravity force present in the universe. It’s called dark energy. The reason we know it’s there is that recent observations have suggested that the rate of expansion of the whole cosmos is increasing. There’s no way that could happen if gravity were the only game in town. Some unseen hand is evidently stretching the fabric of spacetime with greater and greater force as time goes on. Dark energy is, or is equivalent to, antigravity. The next question is: can we learn to harness it? Watch this space.