Driven to Discover

How does a mass create gravity?

2006-10-03T20:31:10Z

Every mass—be it an apple or the sun—distorts space and time, explains Physics and Astronomy professor Serge Rudaz. Gravity, he says, is the manifestation of that distortion.

It’s taken centuries for scientists to fit together the pieces of the gravity puzzle, Rudaz says. In the 17th Century Galileo Galilei put the first piece in place when he discovered that, if you take air resistance out of the equation, all objects fall at the same rate.

]]> Some 60 years later, scientist Sir Isaac Newton contributed the next vital piece of the puzzle. Newton thought that whatever kind of physical law would be used to describe the motion of a falling apple, that the same physical law ought to be used to describe the motion of the moon and the planets. He further proposed that if you have a large mass such as the Earth, then it acts on any other mass in such a way that there is a force between the two of them that’s proportional to the product of their masses and inversely proportional to the square of their distance.

Newton’s methods of calculating the effects of gravity have been reliably used for centuries, most recently enabling scientists to launch the first space probes and plan the moon landings. But one important piece of Newton’s theories couldn’t stand the test of time.

“Newton saw gravity as an instantaneous influence,�? Rudaz says. “If you have a mass, it instantaneously affects the motion of other masses.�?

Early in the 20th century Albert Einstein saw this as a flaw in Newton’s theory and inserted a new piece in the gravitational puzzle—time. A basic ingredient of Einstein’s previous great work, the Special Theory of Relativity, is that the speed of light is a universal speed limit so that nothing in the universe happens instantaneously; everything takes time. With this, and building on the earlier insights of Galileo and Newton, Einstein concluded that clocks tick at differing rates and the lengths of meter sticks will differ depending on whether you are on the Earth, on a satellite orbiting the Earth, or elsewhere in the Universe. Einstein’s new view enabled scientists to map gravitational forces using a curved space/time grid.

One way to visualize it, Rudaz says, is to picture a large rubber mat painted with a grid, with a clock at each point of the grid and with the rule that objects traveling along that grid move at a constant speed in a straight line. Now imagine you place a large mass, like a bowling ball, on the mat. Near the mass, the mat will be indented and the grid distorted. Objects continue across the grid as before, but close to the mass the grid lines will be stretched. An object traversing the grid far away from the mass will not be noticeably affected by the distortion, but one traveling close to the mass will be seen to accelerate because, generally speaking, it will traverse the same number of gridlines in the same amount of time. However, due to the distortion, the gridlines are actually farther apart.

To draw a complete picture, Rudaz says, one must also take into account the gravitational effect on time, which passes slower close to the mass than farther away.

While Newton’s formulation is accurate enough to plan space missions across the Solar System, Einstein’s refinements are required not only to explain a number of very precisely measured astronomical phenomena, but are also at the heart of our modern understanding of the history of the universe. More surprisingly, perhaps, there is an example of everyday technology that serves to confirm Einstein’s views: The distortion of space and time in the Earth’s neighborhood that is prescribed by his theory of gravitation (known as the General Theory of Relativity) must be taken into account to accurately implement the GPS global positioning system.

“According to Einstein, gravity is a manifestation of the variable geometry of space-time, that is, how the lengths of meter sticks and the rates at which clocks keep time are affected by the presence of a mass,�? Rudaz says. “Newton could not have thought of it this way, and he would have been very surprised: For him, time was absolute and, well, meter sticks would have been meter sticks!�?

Serge Rudaz is a professor and director of undergraduate studies in the School of Physics and Astronomy.

What are the chances of intelligent life in outer space?

2006-09-27T20:23:00Z

The odds are “definitely not zero�? and are potentially quite high, according to University astronomy professor Charles “Chick�? Woodward. Additionally, the odds are on the rise, he says, as scientists apply new information to an equation developed in the 1960s to answer just this question.

]]> In 1961, scientist Frank Drake developed The Drake Equation to try to quantify the number of planets in our galaxy capable of producing intelligent life. The equation takes into account factors such as the number of stars in the Milky Way, the fraction of stars that have planets in orbit around them and the number of planets per star that may be capable of evolving intelligent life.

At the time, the exercise was largely conjecture, Woodward says. But using sophisticated new telescopes and research methodologies, scientists are increasingly able to plug real numbers into the equation.

“Certainly we’re right on the cusp of being able to detect earth mass type planets,�? Woodward says. “I think once we do that then the probability begins to go up enormously.�?

But what are the odds that E.T. may be more science than fiction?

“I think the way to look at it is the odds are certainly not zero any more,�? he says. “That is intriguing because I would consider our own galaxy to be a modest-sized galaxy, and to quote Carl Sagan, there are ‘billions and billions’ of galaxies out there, so even if the probability is 1 percent of 10 to the 9th power, you’ve got a big number.�?

Chick Woodward is a professor of astronomy and astrophysics at the University of Minnesota’s Institute of Technology. His research includes the study of solar system comets and dust around evolved stars, using the infrared imaging and polarimetry techniques of the Large Binocular Telescope (LBT) and the Steward Observatory telescope, as well as data from the NASA Spitzer.

What was going on around here before the Big Bang?

2006-09-27T20:12:01Z

This oft-posed question is somewhat nonsensical to Big Bang theorists, says Big Bang expert Keith Olive. That’s because, according to their scientific analysis, the Big Bang was the event that created both space and time. Therefore, there was no “around here�? and no “before�? until the Big Bang occurred.

]]> For people who may have a hard time wrapping their brain around that concept, Olive provides this analogy:

“Imagine, that instead of being three dimensional, space is a two-dimensional surface, and let’s think of that surface as a balloon. Now, let’s think of the radius of the balloon as time. As I blow it up, the surface of the balloon gets bigger. And if I’m watching it as a movie, I’m seeing the balloon at different stages in time where its radius is bigger. Now imagine that the balloon is contracting and it goes down to zero. That balloon is the universe and the Big Bang represents the appearance of the balloon and the beginning of time.�?

Olive acknowledges that some may find these cosmic concepts unfathomable.

“I think it’s hard for people to imagine the space being created, let alone time being created,�? he says. “You can imagine stuff appearing in space at a certain time. That’s what many people imagine: the universe was there, time was going on and then all of a sudden at 5 o’clock was a big explosion and all this matter came out. But that’s not what the Big Bang is. The Big Bang is actually the creation of the space and of the time.�?

Keith Olive is a professor of physics and astronomy at the University of Minnesota. He is involved in several research projects at the University related to the Big Bang and its effects. For more information about Olive’s research, see the article Searching for clues to the early universe.

Will solid matter ever be able to travel at the speed of light?

2006-09-19T20:28:32Z

Solid matter will never travel at the speed of light, according to University physics professor Keith Olive.

]]> “The whole idea of having a limiting velocity is very counter-intuitive,�? he says. “Generally, to make something go faster you give it more energy, but as you approach the speed of light what happens is that instead of the object moving faster, its effective mass increases. Its momentum increases, but not its speed. And so the energy goes right into mass rather than into velocity. You will never get to the point where the velocity equals the speed of light or goes above it.�?

While many science fiction stories rely on objects moving faster than the speed of light as a fundamental plot element, Olive says that’s all the concept is – fiction.

“On television and Star Trek, when they talk about “moving at Warp 6,�? they mean a velocity at six-cubed times the speed of light, or 216 times the speed of light,�? Olive says. “For science fiction it’s essential that you move faster than the speed of light because otherwise, it would take hundreds of thousands of years to cross the galaxy and a few million years to get to other galaxies.�? But, he emphasized, “It’s fictional.�?

“The only things that can move at the speed of light are particles without any mass, like light,�? Olive says. “Nothing with mass could go that fast.�?

Keith Olive is a professor of physics and astronomy at the University of Minnesota. His research areas include cosmology and particle physics.