Since the dawn of humanity, humans have been looking up at the sky and are being fascinated. They wondered where do all these objects like stars, moon and sun come from and how they worked. In the past many people tried to answer these questions and explained the working of the cosmos. These explanations were not based on any evidence or observations. But now, we are living in a golden age of science and technology. We have answered these questions on the basis of evidence and observations. But now, not only humans look up at the stars but they want to go there and settle there. The moon landing was the first step in this quest, that was successfully achieved. The Earth will not remain as it is, forever. In the future, it will be inhabitable for life. So, we have to find a new home for ourselves. Now, our next step is to land humans on the Mars, which is hoped to done in the near future. We can colonize Mars and make human colonies there. But, in the near future solar system will also not be able to sustain life. It is so far from now. But, one day we will have to leave it. Achieving planetary travel is easy but interstellar travel is difficult. We will discuss some of difficulties and some options which could make interstellar travel possible.
Problems Of Interstellar Travel
When it comes to the interstellar travel, a lot of difficulties arise. It's not like ordinary space travel between planets. There are huge distances between stars and are very very far away from each other. Distances between planets are not so small but are of tiny fractions as compared to stars. The nearest star to the sun is "Alpha Centauri A", which is 4.3 light years away. If we traveled at the the speed of light, it would take 4.3 years to reach Alpha Centauri A, which is not possible. Also, if we travel at the speed of light, it will take more than 105,000 years to escape from our galaxy. We would have to travel faster than light to travel beyond our solar system in a shorter time. By our current technology, a spaceship traveling at 80 km/s will reach Alpha Centauri A in 18000 years. The fastest man made object is the "Parker Solar Probe" developed by NASA, launched in 2018, to study sun's outer surface. It hit the maximum speed of 192 km/s. So, with our current technology, it is impossible to travel large distances in space. We are restricted from interstellar travel by our technological limits. But, we can achieve interstellar travel by overcoming these problems. Let's know how we can overcome these problems.
Possible Options For Interstellar Travel
Here are some possible options, which could make interstellar travel possible, faster than light. There are other candidates for interstellar travel, but we will only discuss that could make faster than light travel possible.
Wormholes
Wormholes are one of the predictions made by theory of general relativity. Wormholes, till now are theoretical and exist only on paper in the form of equations. But, they are thought to exist in nature because mathematics works on them. Wormholes connect two very large distances in space. They are like a tunnel, which connects one part of space to another. In reality, if we see a wormhole, it would appear to be round. We can see light coming from the other end of the wormhole giving us a glimpse of the other side. Once crossed, we can see the light coming from the other end, from which we came.
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| Visualization Of Wormhole In 2D |
In the past, we thought of space a an unchanging and absolute entity. But, Einstein's theory of general relativity changed our view of space. Now, we don't think of space as an absolute entity but rather like a fabric which could be bent by mass and also could be torn which could make wormholes possible. Bent in just the right way wormholes could connect two very very distant spots with a short bridge, that we can cross instantaneously, enabling us to even travel faster than speed of light. But, where can we find them?
If string theory and one of it's variations is the correct description of the Universe, then we could be lucky and our Universe might even have a web of wormholes already. Shortly, after the big bang quantum fluctuations at the smallest scale, far far smaller than an atom, may have created many wormholes. Threaded through them are strings known as "Cosmic Strings". In the first billionth of a trillionth of a second after the big bang, the ends of these strings were pulled light years apart, scattering them in the Universe. If wormholes were made in the early Universe with cosmic strings or some other way, they could be all over us.
It is really hard to find a wormhole, but we can try to make one. It is theoretically possible to make a wormhole. There are a few properties that our wormhole should hold in order to be useful. First, it would connect two distant parts in space i.e. Earth and Jupiter. Second, it should not contain any event horizons, which would block two way travel. Third, it should be sufficiently sized, so that gravitational forces don't kill human travelers. The biggest problem we have to solve is to keep our wormhole open. No matter how we make wormholes, gravity tries to close them. No matter what type of wormhole it is, it will try to close unless we have something to keep it open. For the string theory wormhole, it is cosmic string's job to keep it open. For man made wormholes, we need a new ingredient known as "Exotic Matter". It isn't like normal matter or even anti-matter. It is totally new and different having different properties. Exotic mass is the one having negative mass. Positive mass like everything else in the Universe is attractive because of gravity, whereas negative mass would be repulsive, pushing everything away. It acts like an anti-gravity which keeps our wormholes open. Exotic matter would exert enormous pressure to keep wormhole open, more than the pressure inside a Neutron Star. Once we stabilize our wormholes, the ends would start together, so we have to move them to the places we want. We can start by wiring the solar system, leaving one end in orbit around the Earth and other into deep space. The Earth could be a wormhole hub for a vast interstellar human civilization spread over light years.
We only discussed the wormholes with respect to space, however space and time are merged up together and wormholes could also connect to points in time, which would lead to many time travel paradoxes.
Warp Drive Machine
Another possible option for interstellar travel could be a warp drive machine. It was proposed by a physicist Miguel Alcubierre. A warp drive machine does not alter the topology of space by punching a hole and leaping into hyperspace. It simply shrinks the space in front of you while expanding the space behind you. Think of walking across a carpet to reach a table. Instead of walking on the carpet, you could lasso the table and slowly drag it toward you, making the carpet bunch up in front of you. Thus, you have moved little; instead, the space in front of you has shrunk. Recall that space itself can expand faster than the speed of light (since no net information is being transferred by expanding empty space). Similarly, it may be possible to travel faster than the speed of light by shrinking space faster than the speed of light. In effect, when traveling to a nearby star, we may barely leave Earth at all; we would simply collapse the space in front of us and expand the space behind us. Instead of traveling to Alpha Centauri, the nearest star, we are bringing Alpha Centauri to us.
But there is a price to pay. You would have to employ large quantities of both negative and positive energy to power your starship. (Positive energy could be used to compress the space in front of you and negative energy to lengthen the distance behind you.) To use the Casimir effect to create this negative energy, the plates would have to be separated by the Planck distance, 10-33 centimeters—too small to be achieved by ordinary means. To build such a starship, you would need to construct a large sphere and place the passengers inside. On the sides of the bubble, you would put a band of negative energy along the equator. The passengers inside the bubble would never move, but the space in front of the bubble would shrink faster than light, so that when the passengers left the bubble, they would have reached a nearby star. With our current technology, we can't build it, but in the future it could be possible.
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