Things are about to get trippy.
So far we've talked about what spacetime is and why the speed of light is the fastest speed in the universe. Today we're going to explore the first theoretical possibility for using the nature of spacetime to traverse interstellar distances.
This is a 2 dimensional representation of a Lorentzian or Schwarzschild wormhole.
Or an Einstein-Rosen Bridge
Call it what you will, but for our purposes it is a wormhole. A wormhole is basically a tunnel connecting two locations in Minkowski spacetime, with one end opening in one part of spacetime and the other end opening at a different location in spacetime.
To relate this back to our totally simplified explanation of spacetime in Piqued #2, imagine spacetime as a flat mesh everything is sitting on.
Now, imagine you could take an edge of that mesh and fold it over so that one side of the mesh runs parallel to the other side. Then, imagine that you opened two holes and connected those two parallel sheets of space time together. Look at the picture below.
In this image spacetime is folded over itself and a wormhole connects two points. The red arrow represents the normal path you would have to take through spacetime to get from point A to point B. The green arrow represents the short cut the wormhole provides.
Do you see how this could be helpful? A wormhole has the potential to be a kind of cheat code for interstellar travel! By passing through a wormhole, an interstellar traveler would not only cut an immense distance out of their journey, but, in doing so, might even be able to get to their destination "faster" than light.
Here's what I mean.
Let's say you challenge your friend to a race around a 1000 foot long wall.
This is a strange activity, but who am I to judge what you do with your friends?
Your friend is much faster than you, and you know this. But what your friend doesn't know is that you take these races way too seriously and you've built a door in the wall that leads to the other side.
The race starts and your friend sprints off down the length of the wall. When he gets a couple of hundred feet away, you open the door and step through to the other side. A few minutes later your friend arrives beside you, winded.
You won the race, but you didn't run at a faster speed than your friend - you just took a shortcut through the wall rather than going all the way around it.
This is what a wormhole has the potential to provide - a shortcut that allows us, in effect, to travel "faster" than light to a given location in spacetime. But, because at no point are we accelerating up to near light speeds, we don't run into the relativistic problems described in Piqued #3.
So what are we waiting for? Enter the wormhole Number One.
Not so fast.
Even if we found a naturally occurring wormhole, and we haven't, it would almost certainly be very tiny and unstable.
And even if a miracle happened and we found a natural wormhole with an opening big enough for a spaceship to pass through, no one's sure what would be inside. It could be filled high energy radiation, or even a gravitational singularity. There is a good chance entering such a wormhole would get everyone on board killed**
What we need is a traversible wormhole. The problem is, those aren't easy to make.
A traversible wormhole is one which might allow matter, and, we hope, us, to pass through it safely.
The first example of a traversible hole through space time was the Ellis Drainhole, pictured above.
Although Ellis showed a traversible hole in spacetime was mathematically sound, we still had little idea how to make one.
Since Ellis first described his drainhole, several physicists, including Steven Hawking, Kip Thorne and Michael Morris, have postulated that a tiny wormhole, if found, could theoretically be widened, held open, and perhaps made into a traversible wormhole which would allow ships to pass through it. The main requirements for this feat of engineering: sufficient amounts of "exotic matter" with "negative mass", creating large amounts of something called "negative energy" placed at exactly the right spot in the wormhole's opening.
Unfortunately, there's no point getting into the weeds about what all that stuff really is, because we can't make any of it!
To be clear, scientists have observed something akin to negative energy in relation to the Casimir Effect and one group of physicists may have recently made a very small amount of Rubidium with negative mass in a laboratory setting. Nonetheless, humanity is still, if you'll forgive me, lightyears away from ever using a wormhole for interstellar travel.
So, if wormholes are a non-starter right now, what other option might be out there to bridge the great expanse of space.
Next time on Piqued - Warp Drives.
BONUS THOUGHT EXPERIMENT
This isn't really relevant to short cutting interstellar travel, but I wanted to sneak it in anyway cause its hella interesting.
A stable, traversible wormhole might not only be a shortcut across spacetime, but also a kind of time machine.
This Space.com article elaborates on the thought experiment posited by Kip Thorne but here's the gist of it:
Imagine a stable worm hole with one opening in your living room and the other on a space ship.
Your wife gets on the space ship and flies into space at the the speed of light for a total of 12 hours of travel.
As you know from Piqued #3, going that fast makes time for your wife slow down a lot in relation to you. But, as you also know, the passage of time will feel totally normal to your wife on board the ship.
The weird thing is you have a stable wormhole, so you have instantaneous travel from your living room to your wife. The result is that looking through the wormhole, you might also, in essence, be in the same time frame as the ship. You see your wife, can even interact with her, the entire 12 hours she traveled.
Looking through the wormhole, you see your wife arrive back on earth in your front lawn.
But looking out the window, you see nothing, because she doesn't arrive for another ten years!
Nonetheless, you can see her, 12 hours after she left, in the wormhole - ten years in your future.
What happens if, right then, you step into the wormhole? Or she steps into it? Or your future self steps into it?
Time Travel? Maybe. Probably not - It's just a thought experiment, but I thought it worth mentioning.
Source: https://www.space.com/28000-physicist-kip-thorne-wildest-theories.html
Photo Sources:
By Alain r (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons1
By Kes47 (?) (File:LorentzianWormhole.jpg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons2
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By Tobias "ToMar" Maier (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons5
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Author: turningwoodintomarble 7
Informational Sources:
http://www.hawking.org.uk/space-and-time-warps.html
http://www.bbc.com/news/science-environment-39642992
http://www.popsci.com/article/technology/will-wormhole-travel-ever-be-possible#page-2
https://en.wikipedia.org/wiki/Ellis_drainhole
https://en.wikipedia.org/wiki/Wormhole#Traversable_wormholes
https://en.wikipedia.org/wiki/Casimir_effect
https://en.wikipedia.org/wiki/Exotic_matter
http://www.smithsonianmag.com/science-nature/would-astronauts-survive-interstellar-trip-through-wormhole-180953269/