# Space travel to distant galaxies – Niels Bohr Institute - University of Copenhagen

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23 October 2009

# Space travel to distant galaxies

Is it possible to travel with a spaceship to a distant galaxy, located millions of light years out in the universe, and then travel back to the Earth again? Yes, theoretically, says the Australian astrophysicist, Berian James, who has just joined the Dark Cosmology Centre at the Niels Bohr Institute, the University of Copenhagen.

Berian James has, together with two colleagues from the University of Sydney, Juliana Kwan and Geraint Lewis, made calculations for what is required for future space travel to be able to explore as large a part of the universe as possible within a reasonable time period.

### Travel in the Milky Way

With a super advanced spacecraft that could accelerate 9 meters per
second per second and could almost reach the speed of light, a distant
galaxy billions of light years away could be reached. Despite the great
distance only around 50 years would have passed for the astronaut,
because time goes slower onboard the spaceship than on Earth due to
the laws of relativity.

Distances in space are measured in light years. When we say that a star is, for example, 50 light years away, it means it has taken 50 years for the light from the star to reach us on Earth. But no time has passed for the light itself. It is a phenomenon, which is described in the theory of relativity as time dilation. This means that if a rocket travels close to the speed of light, the time that the person in the rocket experiences along the way will be much shorter than the time that has passed on Earth.

The distances in our galaxy, the Milky Way, are thousands of light years, which means the spacecraft must be travelling at quite a speed. If the speed is accelerated constantly to a speed of at least 80 percent of the speed of light, a rocket would cover a distance of 1000 light years, but for the person in the rocket, only 100 years would have passed.

Space travel to other galaxies
With a super advanced spacecraft that could accelerate 9 meters per second per second and could almost reach the speed of light, a distant galaxy billions of light years away could be reached. Despite the great distance only around 50 years would have passed for the astronaut, because time goes slower onboard the spaceship than on Earth due to the laws of relativity.

But there is another very important cosmological parameter in space travel and that is the expansion of the universe. The universe is not static, it is expanding and furthermore the expansion is accelerating, so that means that stars, planets and galaxies are moving away from each other at greater and greater speed.

When calculating the route to the destination point, for example, a distant galaxy, the expansion of the universe means that if the calculations are even 0,1 percent off, it would result in the route of the trip being off by 5 percent – a very great distance, equivalent to missing the mark by millions of light years.

The trip home has its own challenges. Even the smallest uncertainty in the so-called dark energy, which is the force that controls the expansion of the universe, would result in missing the Earth by millions of light years. The spaceship would be ‘lost in space’. But even if you hit the right spot, such a long time would have gone by for those on Earth that the Sun would have long since burned out and life on Earth would be a thing of the past.