Question & Answer

Astrophysics professor J. Richard Gott is continuing in Albert Einstein's route of research in general relativity. His recently released book, "Time Travel in Einstein's Universe," is widely distributed in ten languages. Gott — who has been at Princeton since 1966 — is also known for his innovative classes on astrophysics and general relativity.

'Prince' senior writer Sam J. Cooper sat down with Gott to discuss his theories about the universe, time travel and teaching.

'Prince': Your claim to fame on campus seems to be making science fun and accessible. How did you come to this method of teaching science in this way and making references to H.G. Wells and "Bill and Ted's Excellent Adventure"?

Gott: Science ought to be accessible, and I think that Einstein was picked by Time magazine as the most influential person of the 20th century, and he lived here in Princeton. Princeton's most famous citizen. I think it's important for people to understand what he did.

I think visual aids are important. In one of my lectures, I bring out a pizza to show that the geometry around a cosmic string is like a pizza with a slice missing. One of the things that's interesting about general relativity is that it's a geometrical theory of gravity. You can show people what some of these solutions look like. That helps to make it accessible.

And time travel I think is a fun topic. You mentioned H. G. Wells. It's something people have been fascinated by. It's something there have been science fiction stories about since H. G. Wells' wonderful novel in 1895.

Yes, time travel gives you a window on looking at Einstein's theories on special relativity and general relativity which were some of the most important scientific developments of the 20th century.

In 1905, Einstein showed that time travel to the future was possible. We know this is possible. We've measured that by taking atomic clocks on jet planes.

Einstein showed that moving clocks tick slowly so if you want to visit the Earth a thousand years from now, all you have to do is get on a rocket ship and go at 99.995 times the speed of light, go to a star 500 light years away, come back and the Earth would be a thousand years older. You would have only aged 10 years.

P: Tell me more about your interest in time travel.

G: In 1991, I found an exact solution for two moving cosmic strings in Einstein's general relativity. This had the property that if the strings move fast enough — but still slower than the speed of light — that space time was sufficiently twisted so you could circle the cosmic string while they were passing each other and you could come back and visit an event in your own past.

There's a number of solutions in general relativity like this. The first one [was] discovered in 1949: a rotating universe solution that allowed time travel to the past. Kip Thorn and his associates in 1988 discovered a worm hole solution. I discovered this one using cosmic strings.

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These work because in special relativity, if you can go faster than the speed of light, you can theoretically go back in time . . . You can take a shortcut and beat a light beam by going through a worm hole, going around a cosmic string. So there are solutions in general relativity which are sufficiently twisted to allow time travel to the past.

It's similar to the way Magellan's crew left Europe. They went west west west, around the Earth and came back to Europe again.

P: Why did you bring an upper level seminar on relativity to Princeton? If Einstein were alive today, what would he say about the material you're now teaching and the breakthroughs in astrophysics?

G: Astro. 301 is general relativity for undergraduates for science majors. I started that course when I came here, and I feel it's very important for physics majors to have general relativity. This is Einstein's theory of gravity as curved space time. Just as physics majors take quantum mechanics they should also take general relativity.

It's usually not on the curriculum for undergraduates. It's thought to be too difficult.

But its not so difficult that undergraduates couldn't do it. Graduating as a physics major and never having any general relativity is like being an English major and never taking a course on Shakespeare. I think it's an undergraduate topic.

Years and years ago, people used to postpone calculus until college. Then people said no, high school students can do calculus. General relativity should be on the physics curriculum.

What would Einstein say about the recent developments? When he first developed his general theory of relativity, he applied it to cosmology. Einstein thought the universe was static. No one ever thought about the universe as expanding.

Einstein found that the only way he could make a static universe was by inventing something called the cosmological constant. Today, the cosmological constant is a vacuum energy density — dark energy. It's an energy that even empty space has. It has a negative pressure. It causes a cosmic repulsion . . .

When Hubble in 1929 discovered the expansion of the universe . . . Einstein said, "Oh, that cosmological constant. It's the biggest blunder I ever made in my life." Otherwise, he himself would have discovered the big bang models.

Hubble finds the galaxies are fleeing from us. In recent years, we have found with measurements by supernova, we have found the expansion of the universe is accelerating. That means, it looks like we have a cosmological constant today — a dark energy — that is causing the universe to expand and accelerate. It looks like Einstein was right after all.

If Einstein were around today, he'd find it remarkable that the cosmological constant he produced is doing so well today.

We're at a very exciting time in astronomy because we have the tools that we need . . . The computer revolution has been very helpful to astronomy because we're able to analyze galaxies. We're able to do simulations now that have a billion particles in them . . .

And we have important observatories that are making pathbreaking things. The W-MAP sattelite accurately found the age of the universe — 13.7 billion years, plus or minus 0.2 billion years.

We're getting accurate and interesting cosmological data that's extremely important right at the present time and Princeton people have been involved in that.

P: What problems still confound you, and what problems were you trying to address in your book about Einstein and time travel?

G: We're trying to understand the origin of the universe. The inflationary cosmologies have brought about a wide variety of models.

The early universe is very interesting. There are several different ways people have thought of to start the universe up. Universes can give birth to other universes like branches growing off of a tree. Each branch grows up to be as large as the trunk and sprouts branches of its own. What you end up with is an infinite fractal tree of universes of which we are just one branch.

Then the question is so where does the trunk come from?

One model that Li Xing Li and I considered was that one of the branches can come back and circle around and grow up to become the trunk — this looks like the bottom of a number six. That allows the universe to be its own mother.

Other models that Stephen Hawking have considered involve quantum tunneling: The universe just appears. Other models say it was that the universe is infinitely old.

We're in a situation now where we're beginning to talk about epochs, very close and very early. We're ultimately trying to understand how the universe formed in the first place, which is a key question in cosmology, and very different ideas are out there that people are pursuing.

My book talks about all these things, time travel from the point of view of the future and past. Time travel at the beginning of the universe. I also talk about the Copernican principle and our place in the universe . . .

Time travel gives a window to looking at some of the most important developments in science in the 20th century. I try to explain how Einstein came about these ideas, some of the reasoning that went behind them.