Warp Speed Ahead ?

“NASA May Have Accidentally Created a Warp Field ” went the breathless proclamation.

This was on April 24, 2015 on a site called “Mysterious Universe”. Within a few days the news echoed across the Internet with dozens of websites and newspapers chiming in and the space travel fanatics going gaga.

About a week or two later, scientists tried to push back with a splash of cold reality, but by then the genie had escaped the bottle.

Google the words “NASA warp drive 2015” and you might get the impression that we are off to the stars tomorrow or in a few years at most.

But let’s take a step back.

What is warp drive anyway? What do we need it for ? And is it really in our grasp ?

If science fiction is not your thing (and you are still somehow reading this post), then for your benefit: Warp Drive is a staple of the science fiction series Star Trek, which allows spaceships to travel much faster than the speed of light - putting stars and galaxies within easy reach and allowing folks to “boldly go where no one has gone before”.

Now this is science-fiction.

Anyone with some knowledge of popular science vaguely knows that the speed of light presents some kind of  barrier for space travel and its somehow connected to Einstein.

But what is the obstacle exactly? And why do we think we may be able to get around it at all?

To begin with, one must realize that the “speed of light barrier” comes in two forms – local and global.

Local Speed and the Energy Barrier

Since we are in sci-fi land, imagine a racetrack 3 million kilometres long – which means light takes about 10 second to get from one end to the other.

You sit at the starting line in your hyper-tech antimatter propelled rocket car all geared to make a historic attempt to “break the light barrier”.

A series of speed cameras lines the track from start to finish, spaced 1 meter apart (so there’s 3 billion of them).

At any point on the track, the speed of the car will be measured by the nearest speed camera.

This will be called the local speed of the car.

History will be made if, at any point, the local speed measured exceeds the speed of light (approximately 300,000 km/second).

Well, I’m sorry to disappoint you, but as per Einstein’s Special Theory of Relativity (STR) –which has been verified by thousands of experiments – the effort is bound to fail.

The theory is unequivocal:

The local speed of any object is either always less than light speed, always equal to light speed or always greater than light speed.

To put this in racetrack terms, if any of the cameras clocked your car moving slower than light, then every other camera must do so.

And since your car was presumably standing still at the starting line (as measured by the camera there), its local speed is therefore doomed to be always less than light speed.

But what exactly enforces this speed limit?

What if your car roared past the midpoint mark, moving at 99.9999% of light speed and then you exploded a 100 megaton hydrogen bomb right behind it.

Wouldn’t that push the car past the light barrier?

If not, where does the tremendous energy of the H-bomb go?

(Yes, yes, this is a thought experiment, so assume the car is made of indestructible material like Superman’s costume)

The answer is one of the key subtleties of Relativity.

Let’s assume you exploded your first H-bomb behind the car at the starting line.

What would happen, of course, is a tremendous increase in the velocity of the car.

But at the same time, there would be a slight increase in the car’s mass.

Now, when the car is moving at very close to light speed, say 99.9999%, the effect of the bomb is precisely the reverse.

This time, the mass increases tremendously, while the velocity increase is tiny.

(Incidentally, this is the reasoning which behind E = mc²)

The closer you get to light speed, the more the effect of pushing the car harder – by hydrogen bombs or otherwise – is to primarily increase the mass rather than the velocity.

In fact, when you work out the math, the energy required to accelerate the car all the way to light speed turns out to be infinite – which is just a polite way of saying that it can’t be done !

So to summarize: It is impossible to accelerate any object to reach a local speed equal to, or greater than, the speed of light because that will require an infinite amount of energy.

However, there is no problem if the local speed is always the same as light speed.

(That’s what happens in the case of light itself!)

Similarly, it is theoretically possible to have objects which always move faster than light.

Such hypothetical particles are called Tachyons.

Remember that name as they shall return later in the post to cause much weirdness!

Global Speed and Magic Rubber Tracks

The media hype about your speed record attempt has spread across the Solar System.

So much so, that Alison the astronomer, inhabitant of Mars, has trained her telescope on the race track to see what happens.

Now Alison doesn’t have the benefit of the speed cameras.

However, she can simply measure the time at which your car passed various points on the track and calculate your speed based on her observations.

These calculations give her the global speed of your car.

So, for example, if she sees your car reach the finish line two seconds after starting, then she can conclude that your global speed was 1,500,000 km/second or 5 times the speed of light.

But can she?

Surely, if the car managed to cover 3 million kilometres in two seconds, then at least one of the speed cams would have registered a speed faster than light (which is impossible) ?

Well….not if you have a track made of Magic Rubber.

Imagine your car starting off at a leisurely 1000 km/second.

Now, one second later, at the 1000 km mark, the track instantly str-r-r-r-e-e-e-e-tches behind the car while contracting violently in front of it.

Result: The car is instantly 1000 km from the finish line.

Another second later, the track reverts back to normal.

But the car is now at the finish line!

Thanks to the Magic Rubber track, the car has crossed the track in a mere two seconds and that’s what our Martian astronomer sees.

But what about local speed ? What about the speed cameras ?

Well, notice that the speed cameras get dragged along with the track as it stretches and squeezes.

Since the velocity of the car with respect to the track and hence, the cameras is always 1000 km/second, that’s the speed that the cameras record – there is no local violation of the light speed barrier and relativity theory doesn’t protest.

So, thanks to the Magic Rubber track, the local speed, as per speed cam, is a mere 1,000 km/sec, while the global speed, as per astronomer, is 5 times the speed of light!!

Now if only we knew what this Magic Rubber really is. Turns out we do.

Warp Drive

Magic Rubber is Space itself. Come again?? Okay then…

As per Einstein’s General Relativity, Space is not “mere emptiness”.

It can bend and warp (as in black holes), expand and contract (as with the universe itself) and even oscillate (gravitational waves).

And, yes, under suitable conditions, it can even behave precisely like the Magic Rubber track.

This fact was discovered by Miguel Alcubierre in 1994 and was the basis of a hypothetical propulsion devise called the “Alcubierre Warp Drive” – an attempt to ground the warp drive of Star Trek in genuine science.

But how does one make space stretch and squeeze to order?

Aaah, we have a slight problem there.

Shortly after Alcubierre proposed the warp drive, other physicists quickly determined it would require something extremely weird called exotic matter.

Exotic matter is a completely hypothetical substance which is very strange indeed.

It is not to be confused with matter or even run of the mill antimatter (which is just matter which charges reversed).

It is even different from the dark matter or dark energy you may have heard of lately.

Exotic matter, if it exists at all, would have negative energy and mass.

To see how peculiar this is – suppose you had a ball of regular matter and placed a ball of exotic matter next to it.

Then the regular ball would shoot away from the exotic ball due to gravity. But, the exotic ball would follow it (again due to gravity). And thus you’d have a perpetual chase across the skies!

In fact, attach the balls to adjacent spokes of a wheel, and voila! Perpetual motion.

The attraction-repulsion effect described above makes the wheel spin forever.

Due to this and other peculiarities, many scientists doubt that exotic matter is even possible.

The best candidate for the title is “Quantum vacuum fluctuations in curved space-time”, according to relativity expert Caltech professor Dr. Kip Thorne – and even he isn’t quite sure[1].

This is the grey zone where our understanding of fundamental physics begins to come apart at the seams and further light can’t be shed until we have a working theory of Quantum Gravity.

But let’s suppose that exotic matter does turn out to exist and we got our hands on a big supply.

Would warp drive then become possible and the Universe open up to us?

Errrm… not so fast (literally).

Tachyons and Time Paradoxes

Remember those faster-than-light tachyons we encountered earlier?

They are back to cause some havoc.

So, assume Alice and Bob both have tachyon transmitters which can send messages at, say, 1000 times the speed of light.

Also, let’s assume that Alice is speeding away from Bob at 25% lightspeed.

Now Bob uses his transmitter to send Alice a lewd message.

In return Alice transmits back a virus which causes Bob’s transmitter to self-destruct.

Thus, Bob sends his message, and shortly afterwards, his transmitter explodes.

So far, so unremarkable

But let’s see the story from Alice’s viewpoint.

Alice sees Bob speeding away from her at 25% lightspeed.

She receives his message, sends the virus, and shortly afterwards Bob’s transmitter explodes.

Which all seems fine – until she does some more calculations and finds that Bob sent the message after his transmitter blows up !!

Yes, this happens to be an inevitable consequence of the Lorentz transformations connecting the viewpoints of observers moving with respect to each other.

But wait, if Bob’s transmitter has already exploded, then how did he send the message ?

And if he didn’t send a message, then what did Alice respond to ?

Confused ? You may well be, as what we have on hand is a Time Paradox.

It doesn’t matter whether the tachyons are moving thousands of times faster than light or just a teensy bit quicker, the time paradoxes just keep cropping up.

Most scientists take time paradoxes as proof that faster-than-light tachyons can’t exist.

Other solutions are possible, each of them fairly drastic.

For instance, it is possible that tachyons exists but they don’t interact in any way with ordinary (slower than light) matter. So, it wouldn’t be possible to make tachyonic transmitters or, in fact, construct any means of detecting tachyons either – which means for all practical purposes they don’t exist.

Alternatively, you may have tachyonic transmitters, but some hidden law of nature intervenes whenever you try to set up a time paradox.

For example, the moment Alice tries to transmit her virus, she always ends up pressing the wrong button – although it’s difficult to see how that would work.

Now, where does warp drive come into all this ?

Well, in effect, warp drive works exactly like tachyons.

For example, instead of tachyonic trasmitters, Alice and Bob could use warp drive enabled courier drones to transmit their messages and set up the same contradictory situation as before.

So, all the objections to tachyons would also apply to warp drive.

In Conclusion

Where does all this leave us then ?

For starters, it is impossible to break the local light speed barrier.

Any method of interstellar travel based on locally violating the light speed limit is bound to fail, so don’t even try.

If you try to break the limit globally with warp drive, then you will need supplies of exotic matter, which in all likelihood may not exist.

Even if you could somehow get hold of this strange stuff, some unknown process might throw a wrench into the works to prevent time paradoxes.

Interestingly enough, all the problems above also show up when you try to make Wormholes – an entirely different method of globally travelling faster than light, made famous by the movie Interstellar.

All this leads me – Anindya the Unqualified - to propose the following conjectures:

1) Any conceivable method to travel faster than light – warp drive, wormholes, hyperspace jumps, whatever – will require the use of exotic matter/energy (which may not exist)

2) Any method of travelling faster than light will also permit time travel. A civilization which develops faster-than-light intergalactic travel will also have the key to changing the past !

This suggests that warp drive, wormholes or any conceivable method of faster than light travel is way, way beyond our current technological ability, if not outright forbidden by the laws of nature.

To paraphrase Kip Thorne, the worldwide authority on wormholes, such technology is “probably much further beyond the human race’s present technological capabilities than space travel was for cavemen”.

Regarding warp drive, cosmologist Sean Carroll estimates “The probability for humanity ever developing warp drive is less than one percent. The probability of developing warp drive within the current century is less than one hundredth of a percent”.

To which I will add that the probability of having developed warp drive by accident, as the media articles claim, is less than one millionth of a percent.

Meanwhile, we can console ourselves with the fact that while travel to distant galaxies may forever be impossible, our ever-improving telescopes continue to bring the Universe closer to us in all its beauty and grandeur.

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[1] All Kip Thorne references are from his book “Black Holes and Time Warps”, Chapter 14