Tag Archives: time travel

Theory 2: The Kerr Black Hole

Tara Magill

When we think about time travel and black holes, we usually just imagine circling them and being forced back in time in a similar way to the Tipler Cylinder. However, this next theory draws on the idea that we might actually fly right into the centre of one of the most terror-inducing objects in the universe.

The first realistic concept of rotating black holes was introduced in 1963 by New Zealand mathematician Roy Kerr. He proposed that if dying stars were to collapse into a ring of neutron stars (collapsed stars that are the size of Manhattan but have the density of the Sun), their centrifugal force would prevent them from becoming a singularity. While this sounds complicated, it is relatively simple to understand.

Centrifugal force is the force that draws a rotating body away from its centre of rotation. This is due to the inertia of the body, as the body’s path is constantly changing direction. This is quite easily visualised if you imagine children in on a roundabout – the faster they spin, the more they are pulled away from the centre.

A singularity is slightly more difficult to explain. A simplified version is that a singularity is a point where gravity is mathematically infinite – for example, the centre of a regular black hole. The idea of the Kerr black hole is that it is not a singularity; the centrifugal force of the rotating neutron star will prevent it from becoming one.

As the black hole would not be a singularity, Kerr speculated that it would be safe to enter without fear of its infinite gravity.

It is thought that if these black holes existed, and if we entered one, we would pass through them and exit a white hole. A white hole is essentially the opposite of a black hole; instead of pulling everything into it, it would force everything out – maybe into another time or universe.

While these black holes are entirely theoretical, it could be an interesting way for future generations to explore the past or even the future. After all, there is no telling where (or, when) a Kerr black hole might take you.

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Theory 1: The Tipler Cylinder

Tara Magill

U.S. astronomer Frank Tipler constructed a ‘simple’ method for time travel to the past: first, take a piece of material ten times the mass of the Sun, then squeeze it together and roll it into a long, thin, super-dense cylinder of infinite length. Then, spin the cylinder at a few billion revolutions per minute and see what happens.  Easy, right?

His theory suggests that if a ship was to navigate in a perfect spiral around a Tipler cylinder, they could find themselves billions of years and several galaxies away from where they started. This ship would be on a closed, time-like curve. However, as you can imagine, producing an infinitely long cylinder that is as dense as a black hole has its problems. Namely, at our current level ofImage technological development, it’s impossible.

If we consider this to be a viable theory, however, there are a few things to know before you take off for your journey to the past. Firstly, stay away from the ends of this theoretically infinite cylinder, as distortions here would have an extremely undesirable effect on whoever goes near them. Stick near the centre, and you should hopefully be able to survive the trip.

The way that the Tipler cylinders work is through creating a frame-dragging effect. This means that for objects near the rotating cylinder, their light cones become tilted and part of them turn backwards on the time axis of a space time diagram. This is what allows the spacecraft to travel backwards in time, as they move along this backward-facing light cone. I will be discussing more about light cones in a future entry.

Despite the seemingly obvious practicality issues, Stephen Hawking began attempting to create a more realistic Tipler Cylinder in 1992. However, he came to the conclusion that it is possible to build a Tipler cylinder (of finite length), however, it would have to be built in an area of space which has negative energy but no exotic matter. So, unfortunately, we are unable to travel back in time with this theory, as it’s not possible to create a Tipler Cylinder in the real world under these conditions.

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Time Travel: Is It Possible?

Tara Magill

It is an undisputed fact that science fiction has had a constant influence on contemporary design and engineering. Many pieces of ‘modern’ technology, from flip phones to tablets, have all been represented in episodes of shows such as Star Trek from as far back as the 1960’s, and this trend continues today. Many engineers seek to make possible the ideas of their favourite science fiction writers, and it is this kind of influence that makes science fiction one of the major influences in the zeitgeist of technology. Watch the video below to see some technologies featured in Star Trek that have in fact come true:

ImageTime travel is one of these concepts. While it has been an extreme area of interest for physicists since the beginning of physics itself, it is only recently that we are seeing viable ways to make this dream a reality. However, just because they are viable, does not mean they are possible; at least, not yet. Many of our theories require technology beyond our understanding to be successful, and even if this technology was available, we cannot be sure that our theories would work.

In the following series of articles, I am going to be exploring various time travel theories prevalent in popular culture and determining their viability, while also discussing the much more possible theory of wormholes and FTL (faster-than-light) travel.

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