Solving Einstein’s riddle with an ‘easy’ solution that allows time travel to ‘go back to your past’ | Science | News

General Relativity: A cosmologist discusses Einstein’s theory

It is believed that traveling back in time is physically impossible. However, according to astrophysicist Dr. Paul Sutter of Ohio State University, scientists have envisioned universes where this might not only be possible, but “easy” — and all it takes is a round universe. This idea was found in the work done by Austrian-Hungarian-born researcher Professor Kurt Gödel in 1949.

Professor Gödel – generally considered one of the most important logicians of all time – was a neighbor of the famous physicist Albert Einstein when they both worked at the Institute for Advanced Study in Princeton, New Jersey.

The pair were known to walk together among the institute, although the nature of their conversations was a mystery to the other members of the center.

However, late in life – according to the German economist Oskar Morgenstern – Professor Einstein said that “his own work no longer meant much, and that he only came to the Institute […] For the privilege of going home with Gödel.”

Whatever the couple actually talked about, what is known is that Professor Gödel developed an interest in physics during his time at the institute, and in particular in his friend Einstein’s work on general relativity.

Einstein and time travel

Time travel to the past is possible in one solution to Einstein’s field equations Image credit: Getty Images

The stars revolve in the sky

In a spinning universe, particles can follow “closed time curves” – ending up in their own past Image credit: Getty Images

General relativity explains how objects with mass warp the fabric of space and time, an effect we experience as gravity.

Dr Sutter told Universe Today: “Gödel was curious about whether relativity allowed time travel into the past.

“Einstein’s theory is claimed to be the ultimate framework for the nature of space and time, and as far as we know, time travel into the past is forbidden.

Therefore, Gödel considered that general relativity should automatically prevent it.

Read more: Three dimensions of time and one space for faster-than-light observers

Professor Albert Einstein

Einstein (pictured) developed the general theory of relativity Image credit: Getty Images

Albert Einstein presents a prize to Gödel

Pictured: Einstein gives his friend Kurt Gödel (second from left) a prize Image credit: Getty Images

However, what logic determined was that general relativity could be compatible with time travel into the past – just as long as the universe was in motion.

This very special solution to Einstein’s field equations – known as the Gödel scale, or “Gödel universe” – involves a spinning universe and a special value of 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 universe.

While Einstein set the cosmological constant to zero, Gödel’s solution rotation requires a negative value to counteract the resulting centrifugal force and keep the universe constant

Gödel’s universe has some unusual properties — in particular, how particles in space-time can follow what’s known as a “closed time curve.”

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Distorted alarm clock

Our universe doesn’t spin, so we don’t have to worry about breaking causation Image credit: Getty Images

Dr Sutter explained: “Gödel found that if you follow a certain path in this spinning universe, you can end up in your 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 fall into the trap of the rotation of the universe. This is not just the rotation of things in the universe, but of both space and time themselves.

“In essence, the rotation of the universe will so severely alter your potential paths forward that these paths spin back to where they began.

“You will begin your journey, never traveling faster than the speed of light, and you will find yourself back where you started – but in your past.”

However, there is no need to start worrying about sliding down a closed time curve triggering mind-boggling temporal paradoxes and breaking the web of time.

This is because all cosmological observations by researchers to date indicate that our universe does not rotate.

Dr Sutter concluded: “We are shielded from the Gödel problem of retrograde time travel – but it remains a mystery to this day why general relativity is compatible with this seemingly impossible phenomenon.

Gödel used the example of a spinning universe to argue that general relativity is incomplete—and he may be right.

The Gödel Scale was first described in Reviews of Modern Physics.

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