# What is a Wormhole?

### Wormhole explained

Wormholes can be visualized as portals that can allow entities to travel through space and time. Black holes consist of a point of singularity where all mass is said to accumulate. These black holes consume anything in their proximity. Scientists hypothesize that there also exists a white hole at the other end of a black hole. These white holes spit out the matter, and light, absorbed by the black hole. The entry point and the exit point exist as separate points in the universe. The bridges that link two separate points in space-time are referred to as Einstein-Rosen bridges. This phenomenon of the existence of bridges was predicted in 1935 when Albert Einstein and Nathan Rosen published a paper showing the existence of a corridor or passage directly connecting one part of the universe to another as part of a black hole-white hole system.

These bridges, however, are highly unstable and tend to collapse due to the influence of the gravitational force on them. A wormhole, in this context, is a passage from one point in space-time to another. Each wormhole is expected to have two mouths and a neck, that, serves as a bridge between the two mouths. Proposedly, one mouth of a wormhole is a black hole and at the other mouth is a white hole. Both black holes and white holes are solutions to Einstein’s field equations.

#### Einsteins Field Equation

Einsteins’ Field Equation

where

1. Rμν is the Ricci curvature tensor
2. R is the scalar curvature
3.  gμν is the metric tensor
4.  Λ is the cosmological constant
5. G is Newton’s gravitational constant
6. c is the speed of light in vacuum
7. Tμν is the stress-energy tensor.

A black hole is Schwarzschild’s solution to Einstein’s field equations. Ludwig Flamm discovered the presence of another solution to these field equations while understanding the Schwarzschild’s solution, and this solution was referred to as the white hole. There exists a parameter, called the Schwarzschild’s radius for every entity with mass. This radius is the radius of a sphere such that if all the mass of an object were to be compressed within the sphere of radius equal to the Schwarzschild’s radius, the escape velocity from the surface of the object would equal to the speed of light.

“Embedding diagram” of a Schwarzschild wormhole (Source: wikipedia.org)

Mathematically it could be represented as,

R = 2GM/c2

where,

R is the Schwarzschild’s radius, G is the gravitational constantc is the speed of light, and M the mass of the black hole.

To understand a wormhole through better visualization, we would have to consider the analogy of a piece of paper consisting of two points on it. The two points represent different points in space-time.  For those of you who are absolutely tired of hearing about this analogy (in various movies or explanations), skip the next couple of lines.

For those of you who have not heard of this analogy, pay attention. When the paper is not bent or folded, there is a certain distance between the two points. Now, imagine that the paper is folded, poking a pencil through the paper to connect the two points would provide a shortcut between the points. This distance is seemingly much lesser than the distance between the points had the paper not been folded. A wormhole works in a similar manner to this shortcut. It provides a shortcut between two points in space-time. These points could even belong to different universes.

Wormhole visualized (Credit: Wikimedia Commons)

Wormholes have not been discovered yet. In theory, their existence is proven, but, nobody has ever found one.

Many physicists and astronomers believe that the supermassive black holes that exist at the centre of most galaxies could potentially be wormholes.

### Wormhole vs Black Hole

What’s the difference between black holes and wormholes? Like I have mentioned, wormholes are better explained as passages while a black hole is just a mouth to this passage. Before I get to the specific differences, let’s look at some of the similarities between the two. Both are mathematically consistent. Both distort space and thus both should have matter swirling around them. Both are immensely fascinating, and both have not been fully understood!

This artist’s concept illustrates a supermassive black hole with millions to billions of times the mass of our sun. (Source: NASA JPL)

Now, let’s get to the differences between the two. Recently, we got an image of a black hole whereas wormhole is yet to be found. One more distinguishing factor between black holes and wormholes is the Hawking radiation. Black holes lose energy continuously through the emission of Hawking radiation. This emission is initially slow and builds speed as the process continues. Only black holes are said to emit this Hawking radiation.

Another difference is the lack of an event horizon in wormholes. The event horizon of a black hole is its boundary. To escape from within a black hole, one would have to travel faster than light, at speeds greater than the escape velocity of the black hole.

In black holes, there is no point of return. Once you enter a black hole, there is no escaping it. On the other hand, when you travel through a wormhole, if the wormhole is kept open for a sufficiently long enough time, you could potentially travel back to the same place through the same wormhole. There is a lot of controversy over this theory though since you would not end up going back to the same point in space-time that you initially started at.

Take the below question to quickly test your understanding of wormholes and black holes

Random Quiz

#### How much is the escape speed in Schwarzschild radius?

Correct! Wrong!

The escape velocity from the surface (i.e., the event horizon) of a Black Hole is exactly c, the speed of light. Actually, the very prediction of the existence of black holes was based on the idea that there could be objects with escape velocity equal to c.

Perhaps, the most distinguishing aspect is the fact that wormholes are purely theoretical, while black holes are proven to exist. A black hole is a massive dent in the fabric of space-time that seems to cause a puncture in it. Anything that enters this puncture is consumed and is present at a single point of singularity. A wormhole, on the other hand, can be considered as two punctures in space-time that are connected to one another. The two punctures could exist as any two points in space-time.

### Problems with travel through wormholes

The problems with travel through wormholes arise due to their size and stability. Primordial wormholes are considered to be so small that they are microscopic in nature. Travelling through microscopic wormholes would be highly impossible.

The other problem is the stability of wormholes. Wormholes, under the influence of gravitational forces, tend to collapse rather easily. In order to travel through these wormholes, wormholes should remain open. This requires the presence of Exotic Matter, which, I will cover in the next section. However, this exotic matter also only exists in theory. Keeping a wormhole open is a daunting challenge, indeed.

### Keeping a wormhole open

In the case of wormholes that are existent through the explanations of the string theory, the wormholes are kept open by cosmic strings. In the case of man-made and other wormholes, they would have to be kept open by exotic matter. Exotic matter is a special kind of hypothesized matter. The exotic matter has negative mass. This means that it is repulsive in nature. Positive masses that exist in this universe tend to attract each other, while exotic matter tends to repel.

Due to the presence of gravity, it would not be easy for wormholes to remain open. This exotic matter can counter gravity and allow wormholes to remain open. Exotic matter can be used to weave space and time and sustain wormholes. One candidate for the exotic matter is the vacuum of space.

To understand why the vacuum of empty space could be a potential candidate, you will first have to understand why empty space is not empty. Empty space consists of several virtual particles that are randomly generated. These particles cancel each other out, in pairs. Each pair is said to be a particle-antiparticle pair.

This property, where pairs of particles cancel each other out, can be manipulated to produce similar pairs of matter that cancel each other out. Exotic matter can thus be produced. The exotic matter would provide a great deal of help in the stabilization of wormholes by keeping them open.

Exotic matter, unlike regular matter, would accelerate in directions opposite to the applied force. Despite its peculiar properties and its deviation from the behaviour of normal matter, it is not inconsistent mathematically. It also does not violate the principles of conservation of energy or momentum.

For exotic matter, the mass-energy equivalence would be represented as,

E = -mc2

where,

1. E represents energy
2. m represents mass and
3. c2 is the coefficient of proportionality where c is the speed of light.

The concept that interstellar travel is possible, is most certainly enthralling. The possibilities that can be unlocked through the travel in space-time are enormous and could change how we view the universe entirely. Through such travel, the vastness of the universe could be diminished. We could travel across galaxies and universes and unlock so many secrets of the universe. Although space-time travel has enormous potential, we are hindered by the fact that wormholes, at least for now, only exist in theory.

Eleanor Roosevelt, the former First Lady of the United States once said, “The future belongs to those who believe in the beauty of their dreams”. Maybe, one day we will uncover the secrets of the universe through space-time travel and view the universe in all its glory. Until then, we will have to settle for these dreams of what could be.