Black Hole Travel
How to exploit an Einstein-Rosen bridge to venture deep into the universe
We’ve all seen movies or TV shows where intrepid travelers use a black hole (aka a wormhole) in the same way commuters use the New York subway system: enter at one point and emerge at another, having traveled some enormous distance (or at least a few blocks) in the blink of an eye. Because we’ve seen it depicted in popular entertainments, it must be true: we know everything we see on the screen is always an accurate representation of real life.
People really do fly backward when struck with a bullet. Defibrillators really do re-start inert hearts. DNA evidence really does identify the one person in all the world who did the crime. And black holes really are our convenient cosmic subway system, making lovely wormholes we can saunter through with blissful abandon.
So, as black holes are obviously there for our enjoyment, let’s see how we can use them to venture further than our funny little chemical rockets, futuristic ion drives, or even venture-capital-powered Muskmachines, could take us in a thousand lifetimes.
Like any good recipe, we have to start with our basic ingredients. In this case, lots and lots of mass. Admittedly this is a bit of a problem, as we’ll need to collect several thousand sun-sized stars. But that’s a tiny detail, so let’s assume we can just reach out and pull onto the kitchen table some stars we gathered earlier. Now we crunch them all together until the combined gravitational field is sufficient to bend spacetime in on itself.
At this point we can pause and, should we wish, pour ourselves a well-deserved glass of wine. Personally I find something substantial like an Australian cab from Penfolds goes well with black holes but your tastes may be different. Possibly a Chianti or, for the truly adventurous, a glass or three of Chateau Carbonnieux to accompany a snack of lobster tail gently sautéd in a white wine reduction with just the slightest hint of shaved ginger.
Wiping our lips and moving on, we come to the awkward fact that our pair of black holes must be entangled. No entanglement, no Einstein-Rosen bridge. This is almost identical to what physicists call the soufflé problem: you can’t just grab two hardboiled eggs and crunch them together and hope to get a lovely airy cheese soufflé. No, we have to start with raw eggs, separate the whites, and then whisk them until they form peaks. No peaks, no soufflé. No entanglement, no E-R bridge.
So how do we generate a pair of entangled black holes? I’m glad you asked! Let’s consider some basic physics: if we want to create a pair of entangled photons (perhaps we want to perform the famous quantum eraser experiment, or we’re just showing off to a new acquaintance) we take a photon and pass it through a special kind of prism. This gives us two photons, each half the frequency of the precursor photon. These two photons are now entangled which entitles them to annoy Einstein by performing spooky action at a distance.
Obviously therefore we create a pair of entangled black holes by taking the black hole we made earlier and pushing it through a really big prism.
Yes, there will be some practical issues. First of all, as the event horizon of even quite a small twelve-solar-mass black hole is quite large (approximately 30 kilometers in diameter) it’s clear we will need to go to Prisms-R-Us with a decent sized limit on our credit card. We’ll also need to borrow a pickup truck, as there’s no way we’re going to get that size prism into the back of a family hatchback or even a midsized SUV. Especially as we’ll actually need a prism big enough for a 20,000 solar-mass black hole, as the smallest black hole where the tidal forces won’t rip any human or human-plus-whizzy-spacecraft to shreds must be at least 10,000 solar-masses. And a 10,000 solar-mass black hole will have an event horizon of around 200 million kilometers in diameter. So if we want to start with a 20,000 solar-mass black hole we’re looking at an event horizon of around 500 million kilometers. Obviously our prism will need to be bigger than this, let’s say for the sake of convenience around one billion kilometers along the base.
Let’s hope our pickup truck is large enough to handle the load, right? I’d recommend a Ford F650, but if you’re a RAM enthusiast then I say, go for it! Just don’t bother with a GM product — they always disappoint. Maybe it would also be wise to phone ahead to make sure your local Prisms-R-US has a suitably large prism in stock, so we don’t risk a wasted journey.
Now let’s assume we’ve paid for our giant prism and we’ve brought it home. Next, we have to push our black hole through the prism. Personally I’d advise putting on rubber gloves for this part of the exercise so as to avoid snagging a fingernail or getting calluses. In fact, you may want to push the black hole with a broomstick or, if you have a teenage daughter, you can use one of her used-up boyfriends (teenage girls often hide these under the bed, along with discarded candy wrappers, to avoid embarrassment).
Assuming the black hole doesn’t just annoy us by absorbing the prism, after quite a bit of pushing and prodding we should see a pair of entangled black holes popping out the other side.
And between this pair of entangled black holes is, even though we can’t see it, we know it’s there: an Einstein-Rosen bridge!
Time for another well-deserved glass of wine, I think!
Unfortunately our work is not done. Not by a long chalk. Now we have to move one of the black holes to where we want to emerge once we’ve popped into the other one. I mean, it’s not much use having our two black holes next to each other! Not only is there a major risk of them recombining and undoing our work so far, but it would be silly to go into a black hole in our kitchen merely to pop out of the other one in the downstairs toilet. We want a bit more separation than that for all our efforts and expense!
So now we have to move one of the black holes to some useful destination. Probably not Cancun, maybe not even Tahiti. The reason is that a 10,000 solar-mass black hole will simply absorb the Earth (and in fact pretty much everything in our solar system). Which means we’ll have to take a deep breath and move both of them.
Who knew it was going to be so tough to do something as simple as creating an Einstein-Rosen bridge? Maybe they should have called it an Awful-Lot-Of-Effort bridge.
After another fortifying glass of wine, we can start to move our two black holes in opposite directions. Admittedly this may be a bit tricky. As Newton pointed out (and we all hate a smarty-pants, don’t we?) if we want to move a 10,000 solar-mass black hole then we’ll need energy equivalent to that amount of mass (thanks, Einstein, for that whole e=mc² thing, by the way). So it’s time to refuel up pickup truck and get a-hauling!
Assuming we can pay for the 20,000 solar masses worth of energy we’ll need to nudge our two black holes off in the directions we’ve chosen, we’ll have to wait a bit for the now-moving black holes to get wherever they’re going. Then we’ll need to use up the rest of the balance on our credit cards to pay for another 20,000 solar masses worth of energy to bring them to a halt in the locations we desire. Damn that Mister Newton!
At this point I’d really recommend having another glass of wine, especially as it may have required us to wait several million years to get to this point. Something that ages well, like an old-style heavily oaked Australian Shiraz, would probably be the right tipple to keep our spirits up.
Anyhow, all our efforts have been rewarded. We now have a pair of entangled black holes separated by several thousand million kilometers with an Einstein-Rosen bridge invisibly joining them together. And as we’ve been clever enough to make large enough black holes, anyone using them as an interstellar subway system won’t have to worry (too much…) about being spaghettified by the destructive tidal forces that a smaller event horizon would have generated.
Alas, we’re not finished yet. Time to drain the bottle and perhaps even open another one.
There’s just one tiny little problem with our Einstein-Rosen bridge: nearly all the solutions to the equations that describe the E-R bridge indicate that the spacetime it contains will expand faster than the speed of light. Which means we can pop into one of the black holes but we’ll never get to the other side. Our traverse will be limited by the speed of light (around 300,000 kilometers per second) but the expansion of the internal spacetime inherent in the bridge will expand faster. Worse yet, the more energy we expend trying to traverse the E-R bridge, the faster it will expand because we’ll be adding energy to the system.
The old saying “you can’t get there from here” springs irresistibly to mind.
Perhaps it’s just as well we’ll be trapped inside the ever-expanding E-R bridge. At least then we won’t have the disappointment of remembering that nothing can escape the gravitational field of a black hole. That is why, after all, they’re called black holes! Nothing can ever emerge. Spacetime is so severely warped by the enormous mass of the thing that trying to escape by flying in a straight line away from the black hole carries you right back to its center because the black hole’s gravitational field warps spacetime and turns that straight line into a geodesic. How do you like that solution for the metric tensor, eh?
Stopping to think about it, admittedly at this rather late stage in the game, we have to wonder why all those sci-fi movies and TV shows forgot to mention these awkward little details.
Oh well, at least we can power up the warp drive to get us to the nearest liquor store before it closes for the night. I just hope they speak Klingon…
