# How to “anti-gravity” realize flying

It’s not sitting on an airplane, or carrying equipment similar to a jetpack on its back, but soaring freely in the air like a bird-this is how many people’s dream!
We haven’t realized this dream yet, but a little frog did it first. In 1997, a scientist named Andre Heim threw this frog into a special experimental chamber, but it turned out to be completely ignored. It floats gravitationally in the center of the cabin.
Magical diamagnetism

This cabin is a bit special, it is placed in the center of a device called a “power solenoid”-this device can create a powerful magnetic field. The strength of the magnetic field is usually expressed by the magnetic induction, and its international unit is “Tesla” (symbol is T). So, how strong is the magnetic field of this cabin?
Let us make a simple comparison: the earth’s magnetic field is 0.00003T, the magnet in the home refrigerator is 0.001T, the high-magnetic neodymium magnet is 1.4T, and the magnetic field of this cabin is 16T-16,000 times that of the home refrigerator magnet.
The cabin is spherical, with a diameter of only 3.2 cm. The magnetic field around it is the strongest, and only the magnetic field in the center is weaker. The little frog floats steadily in the center where the magnetic field is weakest.
Later, Andre also won the “Immortal Nobel Prize” for this experiment. So, how did he make this anti-gravity frog?
You might think that Andre might put a magnet in the frog’s body and use the repulsive force generated by the magnet and the magnetic field to overcome the frog’s weight and make it hover in the air. But this is not the case, because if he did this, the result would be that as soon as the frog is thrown into the cabin, it will roll (the magnetic poles will automatically align) and be pulled towards the bottom of the cabin, and then the magnet will be removed from it with great force. Extruded from the body, causing it to burst and die.
However, one thing you might guess right is that there must be something in the frog’s body. In fact, this kind of thing is more convincing than a magnet-as a living creature, frogs were the first to use “diamagnetism.”

Simple magnetic story

Materials can have three types of magnetism: ferromagnetic, paramagnetic, and diamagnetic. We know that materials are composed of atoms. Atoms are divided into nuclei and extranuclear electrons. The electrons are charged and move around the nucleus, and at the same time it is also spinning (rotating by itself). Spinning electrons are like small magnets, with S poles and N poles (related to the spin direction). The magnetism of a material is determined by how many electrons it has and how these electrons spin.
In ferromagnetic materials, there are an odd number of electrons outside the atom (Figure 1). In the inner orbit, electrons with opposite spin directions are paired-like two bar magnets connected together, their magnetic moments are canceled. But in the outer layer, the lonely electron has no “partner”, its spin cannot be cancelled, and it can move around. This means that in the presence of a magnetic field, the electrons align with the direction of the magnetic field, turning the atom into a tiny magnet.
This is why ferromagnetic materials like iron are attracted to any pole of the magnet: when you bring the N pole of the magnet close to the ferromagnetic material, the S pole of the electron is attracted and the N pole is repelled; similarly, the magnet When the S pole is close to the ferromagnetic material, the N pole of the electron is attracted and the S pole is repelled.
Paramagnetism is similar to ferromagnetism. In simple terms, unpaired electrons in a substance are preferentially attracted by nearby atoms (Figure 2). This means that electrons cannot easily rotate when subjected to the force of an external magnet, so the magnetic attraction of atoms will not be so great.
However, if an atom has an even number of electrons, and they can all be paired, the atom will be magnetically neutral (Figure 3). This is the case with atoms in materials like wood-all atoms have pairs of electrons, so they are magnetically neutral, which is why they are not attracted to magnets-such atoms are called diamagnetic atoms.

How does a frog float?

The body of the little frog in the experiment is basically composed of diamagnetic atoms (except for traces of iron and other substances), so it looks like all living things and is magnetically neutral. So how does a super strong magnetic field make it float?
These pairs of electrons can be affected by powerful magnets. When a magnetic field passes through a diamagnetic atom, it induces a current in the atom. At this time, the orbits of the electrons in the atom are no longer random, but will move in the same direction, thereby generating a current that revolves around the atom. This kind of current turns the atom into a tiny electromagnet, but the magnetic field it generates is opposite to the force of the magnetic field exerted on the atom, effectively making the atom repel the magnet (Figure 4).
Now, we can know how the “floating” little frog is produced-when the little frog is placed in the strong magnetic field generated by the machine, its atoms become tiny superconducting magnets, which are the same as the frog’s weight. The force repels the magnetic force in the cabin, so that the little frog loses weight.
The little frog is made up of countless atoms, and this force occurs on every atom, so the little frog will feel really weightless, not like being tied to something and hung up. In other words, its feeling in this cabin will not be different from the feeling in the International Space Station.

Can people float?

With such a cabin, we can carry out research on the “zero gravity environment” on the earth. For example, can the fertilization process of the human body be effectively carried out under weightlessness? Can crops grow well under zero gravity conditions? Will crystallization occur under such conditions? How to make 3D printers work better in zero gravity, and some important problems that humans will face if they emigrate to other planets, and so on.
Having said that, you may want to experience the feeling of weightlessness for yourself-if frogs can do it, why can’t we?
In fact, to make a person float, a super powerful magnet is needed. This magnet must not only have a large magnetic force, but also the range of the generated magnetic field must be able to “cover” the height of the human body. For example, an adult of normal weight needs a magnetic field up to two meters wide and a strength of at least 70T-this will require a huge amount of energy to generate, which may be tens of megawatts. The specific value depends on the person’s own “electromagnetic field”. efficient”.
According to Andrei’s rough estimate, a person weighing 85 kilograms needs about 85 megawatts of energy to float like a frog. what is this concept? For example, we know that Tesla is one of the fastest accelerating cars in the world. The highest power output of its Model S is 615 kilowatts. 85 MW is equivalent to the power output of 138 Tesla Model S at the same time. . Regrettably, there is currently no cabin that allows “humans” to carry out experiments. However, if you are rich enough, you can build your own floating cabin and become the first person to “fly” like this little frog.