The story being reported all over the world is that Harold White of NASA has just built a machine which breaks the laws of Physics. It's called the EMDrive and it's making serious waves...electromagnetic waves! badoom cha! Let's take a look.
Every vehicle ever constructed works on the same principle. Push something backward and you get pushed forwards. When you're pedalling a bicycle the wheel pushes on the Earth and the Earth pushes on the wheel. The Earth is much heavier of course, so it hardly changes what it's doing. The wheel on the other hand is so light that the same force applied will produce a much greater effect, propelling the wheel forwards and tadaa - motion!
Any vehicle which has an engine works exactly the same way, only it uses trillions and trillions of particles of reacting, burning fuel. All engines work by ejecting the fuel backwards, which pushes the vehicle forwards. It works like this:
small mass (fuel) x large acceleration = large mass (vehicle) x small acceleration
It's called Newton's third law and it's fundamental to our understanding of modern engineering. Everything (ever) obeys this law. There's another similar law called the "conservation of momentum principle" which also holds true. The c.o.m.p. says that mass x velocity before a collision (before the fuel collides with the interior of the car) is equal to the mass x velocity afterward. If you add up all the masses and velocities of every particle of fuel and every particle in the vehicle, before and after the vehicle moves, they cancel out perfectly. The universe keeps momentum (mass x velocity) the same everywhere. It is conserved.
Our entire understanding of engineering, mechanics and even movement itself relies on these two principles being true. Every experiment confirms them and we have never had any reason to doubt. That is, until now...
What is the EMDrive?
The EMDrive is a prototype engine which propels an object by exploiting the interaction between EM (Electromagnetic) waves and matter.
How does it work?
The EMDrive is surprisingly simple. You take beams of low-energy light and bounce them around a metal cone. These low-energy light beams are called microwaves - the same invisible beams of light which bounce around inside your microwave oven.
Microwaves don't have mass but they interact with massive objects and cause them to vibrate (that's how a microwave oven works, it vibrates particles in your food, heating them up). The EMDrive uses these microwaves to vibrate the metal cone and by carefully controlling the angle and concentration of the beams, the cone starts vibrating forwards.
The Washing Machine Analogy
Imagine a washing machine vibrating on the floor of your kitchen. It ends up slowly creeping forward because it's pushing against the ground. Now imagine doing that in empty space, where there's no ground beneath it, just a free-floating washing machine. If you turned it on and it started creeping forward you'd have to ask the question...what is it pushing against??? This is essentially where the Scientific community is at right now.
How good is the thruster, if it works?
Pretty good. If the early estimates of White's team are correct, this engine would have the ability to transport us to Mars in a matter of weeks, rather than years. This could genuinely be the device which opens up the solar-system! Travelling to new planets would become equivalent to early sailors in the 19th Century travelling across the Atlantic. It could usher in a new era of space flight and exploration and, as I've pointed out in one of my videos, funding the space program is a good idea for humanity.
What's the Catch?
Well, remember earlier that we established the conservation of momentum principle and Newton's third law? Well the EMDrive pushes the object forward without pushing anything backward. There is no fuel being ejected from the back of the thruster, meaning the cone appears to start moving of its own volition. The equation above has 0 on the left hand side (no force on the fuel), yet the force on the thruster is there. This seems to be impossible. It utterly changes the laws of Physics and as a very wise engineer once said...
So what's going on?
Nobody has a freaking clue. White's team don't even have an explanation for how it works. The research paper details the basic design, the experiments they've conducted and the results they've gotten. But they provide no clear mechanism about how it actually works. So the honest answer to "how do microwaves bouncing around a metal cone generate thrust?" is that we don't know. All we know is that it shouldn't happen...assuming our laws of Physics are correct.
Are the Laws of Physics wrong?
Well, possibly. One of the most important things about Science is that NO LAW IS ABOVE QUESTION. Every theory, even tried-and-tested ones, are still open to doubt. Nothing is known with 100% certainty in Science and we like it that way. If we aren't open to the possibility of correcting ourselves, we never learn anything new!
But Newton's Third Law normally works, right?
To be clear, the third law obviously isn't nonsense because we've tested it repeatedly for centuries and built our entire industrial revolution on it. If it's an approximation, it's a very good one. But, this has happened to Newton before.
In 1687 he published his gravitational law (F = Gma*mb/r^2) which works well on Earth but, it's not quite perfect. The orbit of Mercury deviates from the law slightly because it's close to the Sun and gravity is significantly different there. It took Albert Einstein to work out a more detailed model of gravity in 1915 (General Relativity) which shows that Newton's approach is a "works in most cases" example. It's possible Newton's third law might be due for a similar overhaul.
So, was Newton really all he was cracked up to be?
Yes he was.
What's the alternative to Newton's third law?
We have no idea. This research is five days old (at the time of writing). White's team, in their research paper, put forwad a tentative explanation for what they think might be happening though. They suggest the EMDrive might be pushing against something which doesn't have mass in the normal sense. They propose it might be thrusting against something called "the energy density of the quantum vacuum".
The idea is that empty space isn't really empty; it has a background energy-value to it. Since energy and mass can be treated equivalently (E = mc^2) perhaps the energy of the background can be treated like something with mass. Something we can do work on.
If this is true, it might also solve one of the greatest riddles in modern Physics: the interpretation of the quantum mechanical wavefunction. I don't want to get bogged down here, but it's another mystery of Physics which has stood for to close to 100 years. White's research might be one of the first bits of evidence which shows that "the Bohmian pilot wave interpretation" is true (here's good ol' Wikipedia explaining it). If White's research is validated, he may soon join the illustrious ranks of Richard Feynman, Erwin Schrodinger and Bob Dylan...Sweden beckons?
Who is publishing the research?
Whenever a Scientific claim is made (especially a big one) you have to look at who the people are behind it. Granted, any claim is worth listening to and you don't chuck out a hypothesis because you don't like the person, but if the research is being published by someone who's known for perpetrating engineering hoaxes for example, you might be a little more skeptical.
This research comes straight from NASA's Eagleworks lab, headed by Harold White. Harold White is also the guy who wants to test the Alcubierre "faster-than-light" engine, which is a story for another time. The point is, the Eagleworks lab is a team of talented engineers, looking to find new ways of propelling spacecraft. They aren't a bunch of yahoos working out of their grandmother's basement. These guys are the real deal. It's proper research, done by meticulous Scientists.
How good is their research?
This is the crucial question which now needs to be answered. The paper they've published has been checked by other physicists and passes the preliminary "hmmm, seems potentially legit" test (called peer-review). Now, like any good Scientist, the most important step is to publish, and let the world a) look for mistakes and b) try to replicate their findings.
What we're currently witnessing is Science's strongest weapon: get other people to try and disprove/confirm your idea. It's no good saying you've discovered something if you don't let other people grill you. But now their research is freely available for anyone in the world to look at, and believe me, they will.
If you're interested: here it is
Seriously, give it a read! A lot of cutting edge Physics can be hard to keep up with if you're not fully mathematically literate and don't know all the jargon and notation. But this paper is actually a pretty straightforward read and, as a member of the human race, you have a right to Scientific knowledge! I've read it through a couple of times myself but I'm no expert in engineering. I'm a high-school Physics teacher and this isn't my area of expertise (density functional theory, since you asked). I'm not qualified to make a judgement on whether the research holds up, but thousands of superior Physicsts all over the world, from undergraduates to tenured professors, will be casting their eye over the White paper and scrutinising its every detail in the coming months. If there's a mistake, even a subtle one, someone will find it.
White's paper does outline 9 potential sources of error they could have made (a good Scientist openly points to the flaws in their own argument) but the question is whether these errors are significant, or minor. Sometimes a headline-making news-story turns out to be a mistake (like the faster-than-light-neutrinos thing five years ago) so this one may be pulled apart as well. In fact, to suggest a change to Newton immediately puts you on shaky ground...but the only authority in Science is evidence and if your evidence contradicts Newton, so much for Newton!
So, has NASA just built an impossible machine?
Well, if they really have built it, it's evidently not impossible. What we really want to know is, do we have to change the laws of Physics? I see three logical outcomes:
1) They've just made a mistake in their research.
2) Newton's third law needs to be modified.
3) Newton's third law is still correct, but there's new Physics at work we've never dreamed of
We have to remain skeptical with any claim like this. As Carl Sagan wisely said "extraordinary claims require extraordinary evidence". At the moment, this is a single research paper claiming something seriously weird. Whether their evidence is extraordinary remains to be seen. The line we need to be taking is one of healthy, if optimistic, skepticism. We don't know if NASA has just built a working EMDrive...but we are definitely, most definitely, allowed to get excited!!
EMDrive - from the original White paper
I love science, let me tell you why.