General Relativity: Cosmologist Discusses Einstein’s Theory
Traveling back in time is considered to be a physical impossibility. However, according to Ohio State University astrophysicist Dr. Paul Sutter, scientists have envisioned universes where this might not only be possible, but “easy” — and all it takes is a spinning cosmos. This idea can be found in the work undertaken by the Austrian-Hungarian born researcher Professor Kurt Gödel in 1949.
Professor Gödel – who is commonly regarded as one of the most important logicians of all time – was a neighbor of the renowned physicist Albert Einstein when both worked at the Institute for Advanced Study in Princeton, New Jersey.
The two were known to walk together between the institute, although the nature of their conversations is said to have been a mystery to other members of the center.
However, at the end of his life – according to the German economist Oskar Morgenstern – Professor Einstein said that “his own work no longer meant much, that he came to the Institute only […] to have the privilege of going home with Gödel.”
Regardless of what the pair actually talked about, what is known is that Professor Gödel developed an interest in physics during his time at the Institute, and in particular his friend Einstein’s work on general relativity.
Time travel into the past is possible in a single solution of Einstein’s field equations
In a rotating universe, particles can follow “closed time-like curves” – ending up in their own past
General relativity explains how objects with mass distort the structure of space and time, an effect we experience as gravity.
Dr Sutter told Universe Today: “Gödel was curious if relativity could allow time travel into the past.
“Einstein’s theory claimed to be an ultimate framework for the nature of space and time, and as far as we know, time travel into the past is forbidden.
“So Gödel thought that general relativity should automatically forbid it.”
READ MORE: Three dimensions of time and one of space for faster-than-light observers
Einstein (pictured) developed the theory of general relativity
Pictured: Einstein presenting an award to his friend Kurt Gödel (second from left).
What the logician determined, however, is that general relativity can be compatible with time travel into the past – as long as the universe was set in motion.
This very particular solution to Einstein’s field equations—which is known as the Gödel metric or “Gödel universe”—implies a rotating universe and a special value for the cosmological constant.
In Professor Einstein’s work, the constant was introduced to counterbalance the effect of gravity and achieve a static universe, according to the contemporary understanding of the cosmos.
While Einstein set the cosmological constant at zero, the rotation of Gödel’s solution requires a negative value to resist the resulting centrifugal force and keep the universe static.
The Gödel universe has some very unusual properties – in particular, how particles in spacetime can follow what is known as a “closed time-like curve”.
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Our universe is not rotating, so we don’t have to worry about breaking causality
Dr Sutter explained: “Gödel discovered that if you follow a certain path in this rotating universe, you can reach your own past.
“You would have to travel incredibly far – billions of light years – to do that, but it can be done.
“As you travel, you will be caught up in the rotation of the universe. This is not only a rotation of things in the cosmos, but of both space and time itself.
“Essentially, the rotation of the universe would alter your potential forward paths so strongly that those paths go all the way back to where you started.
“You would set out on your journey and never travel faster than the speed of light and find yourself back where you started, but in your own past.”
However, there’s no need to start worrying about slipping down a closed time-like curve and triggering mind-boggling temporal paradoxes and breaking the web of time.
This is because all cosmological observations by researchers to date suggest that our universe is not rotating.
Dr Sutter concluded: “We are protected from Gödel’s problem of backward time travel – but it remains a mystery to this day why general relativity agrees with this seemingly impossible phenomenon.
“Gödel used the example of the rotating universe to argue that general relativity is incomplete—and maybe he’s right after all.”
The Gödel metric was first described in the journal Reviews of Modern Physics.