Physicist Brian Greene taught audience members how to see in 10 dimensions at the Lobero Theatre Sunday night.
A leading string theorist and a member of UCSB’s Kavli Institute for Theoretical Physics, Greene recounted the highlights of his book, The Elegant Universe. After going over the physics background necessary to understand string theory, Greene drew audible “wows” from the audience when he explained the core underpinnings of string theory, and how our understanding of the universe could subsequently change.
Greene was introduced by Chris Carter, producer and writer of the TV show, “The X-Files.” Carter recalled reading Greene’s book and thinking about the implications of these new ideas in physics. Sometimes the reality of what theoretical physics predicts is hard to grasp, even for a science fiction writer.
“As strange as ‘The X-Files’ could be, we never got as far out as this guy,” Carter said.
Theoretical physics describes a branch of science that tries to explain physical phenomena by using mathematics and careful thought instead of empirical measurements. Greene hailed Albert Einstein as the most influential theoretical physicist in history.
“He changed the ideas of space and time,” Greene said.
Einstein’s first major contribution to the modern understanding of physics was the introduction of the ultimate speed limit – the speed of light, Greene said. Before this maximum speed limit was introduced, scientists thought some things could happen instantaneously, like gravity. Newton’s law of gravitation states that the attraction felt between two objects is instantaneous. Einstein stated that this is not possible. Nothing – no signal, no information, no influence – can travel faster than the speed of light.
Light has been measured to travel at 186,000 miles per second. The sun is so far away that even at that tremendous speed, it takes nearly eight minutes for the its light to reach the Earth. If the sun disappeared right now, we could not possibly know until eight minutes had passed. Earth’s gravitational attraction to the sun holds the planet in orbit. If gravity acted instantaneously and light did not, the earth would leave its orbit before the darkness accompanying the sun’s disappearance reached it.
“The fact that there is a speed limit is a problem for Newton’s Law,” Greene said.
Greene said that Einstein’s second major contribution was his theory of general relativity. This theory provides a way to understand how gravity works while still obeying the maximum speed limit. In fact, Einstein’s calculations proved that the speed of gravity should be exactly the same as the speed of light. Greene said the reason Einstein has been praised so much is because his ideas unified two things – the speed of light and the speed of gravity. Physical theories that unify separate phenomena are always desirable because they approach the idea that there is one singular theory that could explain everything in the universe, Greene said.
To explain general relativity, Greene used the analogy of a thin horizontal rubber sheet. If the sheet was perfectly flat, a marble placed on the sheet would have no tendency to roll in any direction. If a bowling ball was placed on the sheet, it would form a large depression. The marble would roll down into the depression, toward the bowling ball. The heavier the bowling ball, the bigger the depression, and the faster the marble will would roll toward it. If the bowling ball were removed very quickly, the rubber sheet would take a short time to return to its flat shape. That amount of time is analogous to the speed of gravity.
“Gravity is the fabric of space and time,” Greene said. “Einstein’s theory works just a little better than Newton’s.”
In the case of the sun disappearing, general relativity states that the earth would remain in orbit for eight minutes after the sun is gone. This is the time it would take for the gravity wave to reach earth and release it from the depression in space that is currently holding it the sun’s orbit.
Besides relativity, there is another area of physics that has changed markedly in the last century. This field is called quantum theory, and it describes how physics works on a very small scale. Greene said that on a macro scale, the warping of space is very smooth, like a smooth depression in a rubber sheet. On the micro scale, space is not smooth. It is constantly churning and moving, like the surface of boiling water. Quantum theory describes this rapid and chaotic motion, and has some startling physical conclusions.
“If you fire a particle like an electron at a barrier that classically it could not penetrate, quantum theory says there is a small chance it can,” Greene said.
Greene went on to say that there is even a chance that he could walk into a solid stone column and come out on the other side. The probability is extremely low, but it is not zero according to quantum theory.
String theory provides a way to unify the smoothness of macro space and the roughness and chaos of micro space, Greene said. The basic concept of string theory is that every piece of matter in the universe is composed of very small vibrating loops of string. The pattern of vibrations, much like the pattern of vibrations on the string of a musical instrument, determines the properties of the particle it composes, Greene said.
The dilemma is that the mathematics behind string theory require the tiny loops of string to vibrate in 10 dimensions. This is a problem because no person has ever seen more than three dimensions. This conclusion does not daunt string theorists like Greene. He explained one way in which the other seven dimensions could be hidden to observers by rolling up a sheet of paper. If the flat plane of paper represented space, it has two dimensions: top to bottom, and left to right. If the paper is rolled up into a cylinder, the left to right [[left-to-right]] dimension is unchanged, but the top to bottom [[top-to-bottom]] dimension is changed into clockwise or counterclockwise. If the paper is rolled tighter, the cylinder will be come very thin, and from afar it may look like a simple line with no rolled-up clockwise dimension. This may be how the seven other dimensions of string theory are hidden.
Greene said that string theory could be strengthened by observational data from space. When the universe was young, the strings that made up all matter were very energetic. As the universe cooled down and expanded, the imprint left from the energetic strings may have remained. Thus, there could be large, string-shaped artifacts in space waiting be found that would provide evidence for string theory.
“Nothing to me would be more poetic; no outcome would be more graceful … than for us to confirm our theories of the ultramicroscopic makeup of spacetimea and matter by turning our giant telescopes skyward and gazing at the stars,” Greene said.