Gateway to the Stars: Wormholes

By Ria Srivastava


It took 9.5 years for the New Horizons spacecraft just to get to Pluto which is still within our solar system. The nearest star (after our Sun) is more than 40 trillion kilometers away! Wouldn’t it be convenient if the universe offered us a shortcut?

What is a Wormhole?


Spaceships on Star Trek: Deep Space 9 regularly take a shortcut between distant parts of the Universe by traveling through a wormhole, a kind of spacetime tunnel.


Albert Einstein’s theory of general relativity profoundly changed our thinking about fundamental concepts in physics, such as space and time. But it also left us with some deep mysteries. One was black holes, which were only detected over the past few years. Another was “wormholes” — bridges connecting different points in spacetime, in theory providing shortcuts for space travellers.


As the theory allows the fabric of spacetime to be stretched and bent, one can imagine all sorts of possible configurations. You can picture a wormhole as a kind of tunnel that connects two points in spacetime. That tunnel could be a straight chute or take a more winding path. If the wormhole is ‘traversable,’ it acts as a shortcut through spacetime, connecting two points that would otherwise be far apart.



A traversable wormhole would be a shortcut through space.

Types of Wormholes


  1. Einstein-Rosen Bridge


In 1935, Einstein and physicist Nathan Rosen described how two sheets of spacetime can be joined together, creating a bridge between two universes. This is one kind of wormhole: it would look like a black hole on one end, and an anti-black hole, or white hole, on the other end. A white hole acts like the reverse of a black hole by emitting energy while not allowing anything to enter. However, this wormhole won’t be traversable because it takes infinite amounts of time to cross over to the opposite universe and they close shut in the middle.


An Einstein Rosen Bridge

2. Primordial String Theory Wormholes


If string theory or one of its variations is the correct description of our universe, then our universe might even have a tangled web of wormholes already. Shortly after the Big Bang, quantum fluctuations (In quantum physics, a quantum fluctuation is a temporary random change in the amount of energy in a point in space) at the smallest scales, far, far smaller than an atom may have created many, many traversable wormholes. Threaded through them are strings called cosmic strings. The cosmic strings keep the wormholes open against gravity. In the first billionth second of the Big Bang, the ends of these tiny, tiny wormholes were pulled light years apart scattering them through the universe. These wormholes may still be around today, waiting to be discovered.


Space-time after the Big Bang with primordial wormholes.

3. Artificial Wormholes


To be traversable and useful, wormholes need to have certain properties. First, it must connect to distant parts of space-time. Second, it should not contain any event horizons, (an event horizon is the boundary defining the region of space around a black hole from which nothing, not even light, can escape) which would block two-way travel. Thirdly, it has to be sufficiently large and kept open against the force of gravity, which tries to close them. Physicists have discovered that the presence of exotic matter can hold a wormhole open.


Exotic matter, not to be confused with dark matter, is a form of matter that has negative energy density and negative pressure and is repelled rather than attracted by gravity. Exotic matter must exert enormous pressure to push space-time open, greater than even the pressure of the centres of neutron stars. So far exotic matter usually comes in the form of particles in quantum experiments so no one knows if enough exotic matter to build a wormhole can exist all in one place.


The vacuum of space itself may work as exotic matter. Quantum fluctuations in empty space constantly creates pairs of particles and antiparticles, only for them to be annihilated an instant later. The vacuum of space has millions of such fluctuations taking place, and we can already manipulate them to produce an effect similar to exotic matter, which could be used to stabilize the wormhole. This way we could leave one end of a wormhole in orbit around the earth with the other end in deep space.



Can we prove that wormholes exist?


In a new paper, published in the Monthly Notices of the Royal Society, Russian astronomers suggest they may exist at the centre of some very bright galaxies, and propose some observations to find them. This is based on what would happen if matter coming out of one side of the wormhole collided with matter that was falling in. The calculations show that the crash would result in a spectacular display of gamma rays that we could try to observe with telescopes.


This radiation could be the key to differentiating between a wormhole and a black hole, as they seem to be indistinguishable from the outside. Black holes should produce fewer gamma rays and eject them in a jet, while radiation produced via a wormhole would be confined to a giant sphere. Although the kind of wormhole considered in this study is traversable, it would not make for a pleasant trip, because it would be so close to the centre of an active galaxy that the high temperatures would burn everything to a crisp. But this wouldn’t be the case for all wormholes, such as those further from the galactic centre.


Potential of Wormholes


Wormholes are a popular subject among science fiction enthusiasts and theoretical physicists alike because such shortcuts would open up a universe of possibilities. We could travel to another galaxy in a human lifetime or explore the existence of parallel universes. They also allow the possibility of time travel. We could go back to the early days of our solar system’s formation and settle the debate over how our moon formed or solve the mystery of how the supermassive black hole at the center of the Milky Way came to be, for starters.


Dark Side of Wormholes


However, opening even a single wormhole breaks the universe in fundamental ways, potentially creating time travel paradoxes and violating the causal structure of the universe. Even if we could prop a wormhole tunnel open with the gravity repelling abilities of exotic matter, other theorists, like Stephen Hawking, have suggested that once anything, even a single particle, enters a wormhole, mathematics requires that the wormhole collapses.

That does not bode well for intergalactic space and time travel. So for now, wormholes only exist in our imagination, and on paper in the form of equations.


References

  1. Are Wormholes Real? ( 2019, March 12) https://www.quickanddirtytips.com/education/science/are-wormholes-real?utm_source=sciam&utm_campaign=sciam

2. Wormholes Explained- Breaking Spacetime (2018, August 12) Content and images 1, 2 and 3. https://www.youtube.com/watch?v=9P6rdqiybaw


3. Wormholes may be lurking in the universe — and new studies are proposing ways of finding them. (2021, January 14) Content and image 4.

https://www.downtoearth.org.in/blog/science-technology/wormholes-may-be-lurking-in-the-universe-and-new-studies-are-proposing-ways-of-finding-them-75055


4. Wormhole Construction: Proceed with Caution. (1998, August 3)

https://physics.aps.org/story/v2/st7