One of the most surprising facts in science is how universal the laws of nature are. Each particle obeys the same rules, experiences the same forces, exists in the same fundamental constants, regardless of where and when it is. From the point of view of gravitation, each individual particle of the Universe experiences the same gravitational acceleration or the same curvature of space-time, regardless of what properties it has.
In any case, it follows from the theory. In practice, some things can be very difficult to measure. Photons and ordinary stable particles fall equally, as expected, in a gravitational field, and the Earth causes any massive particle to accelerate towards its center at a speed of 9.8 m / s2. But no matter how we tried, we have never been able to measure the gravitational acceleration of antimatter. It should accelerate in the same way, but until we measure it, we cannot be sure. One of the experiments is aimed at finding the answer to this question, once and for all. Depending on what he finds, we may be one step closer to the scientific and technological revolution.
Does anti-gravity exist?
You may not be aware of this, but there are two completely different ways to represent mass. On the one hand, there is mass that accelerates when you apply force to it: that's m in Newton's famous equation, where F = ma. It's the same with Einstein's equation E = mc2, from which you can calculate how much energy you need to create a particle (or antiparticle) and how much energy you get when it annihilates.
But there is another mass: gravitational. It is the mass, m, that appears in the weight equation on the Earth's surface (W = mg) or Newton's gravitational law, F = GmM / r2. In the case of ordinary matter, we know that these two masses - inertial and gravitational masses - should be equal to the nearest 1 part in 100 billion, thanks to experimental constraints set more than 100 years ago by Laurent Eotvos.
But in the case of antimatter, we could never measure all of this. We applied non-gravitational forces to antimatter and saw it accelerate; we created and destroyed antimatter; we know exactly how its inertial mass behaves - just like the inertial mass of ordinary matter. F = ma and E = mc2 works in the case of antimatter in the same way as with ordinary matter.
But if we want to know the gravitational behavior of antimatter, we cannot simply take theory as a basis; we have to measure it. Fortunately, an experiment is under way to find out exactly that: the ALPHA experiment at CERN.
Promotional video:
One of the big breakthroughs that has happened recently has been the creation of not only particles from antimatter, but also neutral, stable bound states in them. Antiprotons and positrons (antielectrons) can be created, slowed down, and forced to interact with each other to form neutral antihydrogen. Using a combination of electric and magnetic fields, we can confine these antiatoms and keep them stable away from matter, which would lead to annihilation in the event of a collision.
We have been able to successfully keep them stable for 20 minutes at a time, far beyond the microsecond timescales that unstable fundamental particles typically experience. We fired photons at them and found that they have the same emission and absorption spectra as atoms. We have determined that the properties of antimatter are the same as predicted by standard physics.
Except for gravitational ones, of course. The new ALPHA-g detector, built at the Canadian factory TRIUMF and shipped to CERN earlier this year, should improve the limits of the gravitational acceleration of antimatter to a critical threshold. Does antimatter accelerate in the presence of a gravitational field on the Earth's surface to 9.8 m / s2 (down), -9.8 m / s2 (up), 0 m / s2 (in the absence of gravitational acceleration), or to some other value ?
From both a theoretical and practical point of view, any result other than the expected +9.8 m / s2 will be absolutely revolutionary.
An analogue of antimatter for each particle of matter should have:
- the same mass
- the same acceleration in a gravitational field
- opposite electric charge
- opposite spin
- the same magnetic properties
- should bind in the same way into atoms, molecules and larger structures
- should have the same spectrum of positron transitions in a variety of configurations.
Some of these properties have been measured over time: the inertial mass of antimatter, electric charge, spin and magnetic properties are well known and studied. The binding and transient properties were measured by other detectors in the ALPHA experiment and are in line with the predictions of particle physics.
But if the gravitational acceleration turns out to be negative rather than positive, it will literally turn the world upside down.
Currently, there is no such thing as a gravitational conductor. On an electrical conductor, free charges live on the surface and can move, redistributing themselves in response to any charges nearby. If you have an electrical charge outside the electrical conductor, the inside of the conductor will be shielded from that source of electricity.
But there is no way to protect oneself from the force of gravity. There is no way to tune a uniform gravitational field in a specific area of space, such as between parallel plates of an electric capacitor. Cause? Unlike electrical force, which is generated by positive and negative charges, there is only one type of gravitational "charge" - mass / energy. The gravitational force always attracts and there is no way to change it.
But if you have negative gravitational mass, everything changes. If antimatter actually manifests anti-gravitational properties, falls up and not down, then in the light of gravity it consists of anti-mass or anti-energy. According to the laws of physics as we know it, there is no anti-mass or anti-energy. We can imagine them and imagine how they would behave, but we expect antimatter to have normal mass and normal energy when it comes to gravity.
If anti-mass does exist, the many technological advances that science fiction writers have dreamed of for many years will suddenly become physically feasible.
- We can create a gravitational conductor by shielding ourselves from gravitational forces.
- We can create a gravitational capacitor in space and create an artificial gravity field.
- We could even create a warp drive, since we would have the ability to deform spacetime in the same way as the mathematical solution of general relativity proposed by Miguel Alcubierre in 1994 requires.
This is an incredible opportunity that is considered nearly impossible by all theoretical physicists. But no matter how wild or unthinkable your theories are, you must support them or refute them exclusively with experimental data. Only by measuring and testing the universe can you know exactly how its laws work.
Until we measure the gravitational acceleration of antimatter with the precision necessary to determine whether it is falling up or down, we must be open to the possibility that nature is not behaving the way we expect it to. The principle of equivalence may not work in the case of antimatter; it can be 100% anti-principle. And in this case, a world of completely new possibilities will open up. We will find out the answer in a few years, by conducting a simple experiment: put an antiatom in a gravitational field and see how it will fall.
Ilya Khel