Physical phenomena that do not recognize any speed limits.
The upper speed limit is known even to schoolchildren: by connecting mass and energy with the famous formula E = mc2Albert Einstein, back in the early twentieth century, pointed out the fundamental impossibility of anything with mass to move in space faster than the speed of light in a vacuum. However, this formulation already contains loopholes that some physical phenomena and particles are quite capable of bypassing. At least, the phenomena that exist in theory.
The first loophole concerns the word "mass": Einstein's restrictions do not apply to massless particles. They also do not apply to some rather dense media, in which the speed of light can be significantly less than in a vacuum. Finally, when sufficient energy is applied, space itself can deform locally, allowing it to move in such a way that for an observer from the outside, outside this deformation, the movement will occur as if faster than the speed of light.
Some of these "superfast" phenomena and particles of physics are regularly recorded and reproduced in laboratories, even applied in practice, in high-tech instruments and devices. Others, predicted theoretically, scientists are still trying to discover in reality, and on the third they have big plans: perhaps someday these phenomena will allow us to move around the Universe freely, not even being limited by the speed of light.
Quantum teleportation
Status: actively developing
The teleportation of a living creature is a good example of a technology that is theoretically permissible, but practically, apparently, never possible. But if we are talking about teleportation, that is, the instant movement from one place to another of small objects, and even more so particles, it is quite possible. To keep things simple, let's start simple - particles.
It seems that we will need devices that (1) completely observe the state of the particle, (2) transfer this state faster than the speed of light, (3) restore the original.
However, in such a scheme, even the first step cannot be fully implemented. The Heisenberg uncertainty principle imposes insurmountable limits on the accuracy with which the "pair" parameters of a particle can be measured. For example, the better we know its impulse, the worse - the coordinate, and vice versa. However, an important feature of quantum teleportation is that, in fact, you don’t need to measure particles, just as you don’t need to restore anything - you just need to get a pair of entangled particles.
For example, to prepare such entangled photons, we need to illuminate a nonlinear crystal with laser radiation of a certain wave. Then some of the incoming photons will decay into two entangled - inexplicably linked, so that any change in the state of one instantly affects the state of the other. This connection is really inexplicable: the mechanisms of quantum entanglement remain unknown, although the phenomenon itself has been and is being demonstrated constantly. But this is such a phenomenon, in which it is really easy to get confused - suffice it to add that before measurement, none of these particles has the desired characteristics, and whatever result we get by measuring the first, the state of the second will strangely correlate with our result …
The mechanism of quantum teleportation, proposed in 1993 by Charles Bennett and Gilles Brassard, requires adding only one additional participant to the pair of entangled particles - in fact, the one we are going to teleport. It is customary to call senders and receivers Alice and Bob, and we will follow this tradition by giving each of them one of the entangled photons. As soon as they disperse a decent distance and Alice decides to start teleportation, she takes the desired photon and measures its state together with the state of the first of the entangled photons. This photon's indefinite wavefunction collapses and instantly responds in Bob's second entangled photon.
Unfortunately, Bob does not know exactly how his photon reacts to the behavior of Alice's photon: to understand this, he needs to wait until she sends the results of her measurements by regular mail, no faster than the speed of light. Therefore, no information can be transmitted through such a channel, but the fact will remain a fact. We teleported the state of one photon. In order to transfer to humans, it remains to scale the technology, embracing every particle of only 7000 trillion trillion atoms of our body - it seems that no more than eternity separates us from this breakthrough.
However, quantum teleportation and entanglement remain some of the hottest topics in modern physics. First of all, because the use of such communication channels promises unbreakable protection of transmitted data: in order to gain access to them, attackers will need to seize not only the letter from Alice to Bob, but also access to Bob's entangled particle, and even if they manage to get to it and do it measurements, this will forever change the state of the photon and be immediately revealed.
Vavilov - Cherenkov effect
Status: used for a long time
This aspect of traveling faster than the speed of light is a pleasant occasion to remember the achievements of Russian scientists. The phenomenon was discovered in 1934 by Pavel Cherenkov, who worked under the direction of Sergei Vavilov, three years later it received a theoretical basis in the works of Igor Tamm and Ilya Frank, and in 1958 all participants in these works, except for the already deceased Vavilov, were awarded the Nobel Prize for physics.
Indeed, the theory of relativity speaks only of the speed of light in a vacuum. In other transparent media, light slows down, and quite noticeably, as a result of which refraction can be observed at their border with air. The refractive index of glass is 1.49, which means that the phase speed of light in it is 1.49 times less, and, for example, diamond has a refractive index of 2.42, and the speed of light in it is more than halved. Nothing prevents other particles from flying and faster than light photons.
This is exactly what happened with electrons, which in Cherenkov's experiments were knocked out by high-energy gamma radiation from their places in the molecules of the luminescent liquid. This mechanism is often compared to the formation of a sound shock wave when flying in the atmosphere at supersonic speed. But you can also imagine running in a crowd: moving faster than light, electrons rush past other particles, as if touching them with a shoulder - and for every centimeter of their path, forcing them to angrily emit from several to several hundred photons.
Soon, the same behavior was found in all other fairly clean and transparent liquids, and subsequently Cherenkov radiation was recorded even deep in the oceans. Of course, photons of light from the surface do not really reach here. On the other hand, ultrafast particles that fly out from small amounts of decaying radioactive particles from time to time create a glow, perhaps at the very least allowing the locals to see.
Cherenkov-Vavilov radiation has found application in science, nuclear power and related fields. The reactors of the nuclear power plant, chock-full of fast particles, glow brightly. By accurately measuring the characteristics of this radiation and knowing the phase velocity in our working environment, we can understand what kind of particles caused it. Astronomers also use Cherenkov detectors, detecting light and energetic cosmic particles: heavy ones are incredibly difficult to accelerate to the required speed, and they do not create radiation.
Bubbles and burrows
Status: fantastic to theoretical
Here is an ant crawling on a sheet of paper. Its speed is low, and it takes the poor fellow 10 seconds to get from the left edge of the plane to the right. But as soon as we take pity on him and bend the paper, connecting its edges, he will instantly "teleport" to the desired point. Something similar can be done with our native space-time, with the only difference that the bending requires the participation of other, imperceptible to us dimensions, forming tunnels of space-time - the famous wormholes, or wormholes.
By the way, according to new theories, such wormholes are a kind of space-time equivalent of the already familiar quantum entanglement phenomenon. In general, their existence does not contradict any important concepts of modern physics, including the general theory of relativity. But to maintain such a tunnel in the tissue of the Universe, something will be required that bears little resemblance to real science - a hypothetical "exotic matter" that has a negative energy density. In other words, it must be the kind of matter that causes gravitational … repulsion. It is hard to imagine that someday this exotic will be found, let alone tamed.
An even more exotic deformation of space-time - movement inside the bubble of the curved structure of this continuum - can serve as a kind of alternative to wormholes. The idea was expressed in 1993 by the physicist Miguele Alcubierre, although in the works of science fiction writers it sounded much earlier. It's like a spaceship that moves, squeezing and crushing space-time in front of its nose and smoothing it back again. At the same time, the ship itself and its crew remain in the local region, where space-time retains its usual geometry, and do not experience any inconvenience. This is clearly seen in the popular among dreamers of the series "Star Trek", where such a "warp drive" allows you to travel, without modesty, throughout the Universe.
Tachyons
Status: fantastic to theoretical
Photons are massless particles, like neutrinos and some others: their mass at rest is zero, and in order not to disappear completely, they are forced to always move, and always - at the speed of light. However, some theories suggest the existence of much more exotic particles - tachyons. Their mass, appearing in our favorite formula E = mc2, is given not by a simple, but by an imaginary number, including a special mathematical component, the square of which gives a negative number. This is a very useful property, and the writers of our beloved Star Trek series explained the work of their fantastic engine by “harnessing the energy of tachyons”.
Indeed, the imaginary mass does the incredible: tachyons must lose energy, accelerating, so for them everything in life is not at all the same as we used to think. Colliding with atoms, they lose energy and are accelerated, so that the next collision will be even stronger, which will take even more energy and again accelerate the tachyons to infinity. It is clear that such self-infatuation simply violates basic causal relationships. Perhaps that is why only theorists are studying tachyons so far: no one has yet seen a single example of the decay of cause-and-effect relationships in nature, and if you see, look for a tachyon, and the Nobel Prize is guaranteed to you.
However, theorists still showed that tachyons may not exist, but in the distant past they could well have existed, and, according to some ideas, it was their infinite possibilities that played an important role in the Big Bang. The presence of tachyons explains the extremely unstable state of a false vacuum, in which the Universe could have been before its birth. In such a picture of the world, tachyons moving faster than light are the real basis of our existence, and the emergence of the Universe is described as the transition of the tachyon field of the false vacuum into the inflationary field of the true one. It is worth adding that all these are quite respected theories, despite the fact that the main violators of Einstein's laws and even the cause-and-effect relationship turn out to be the founders of all causes and effects in it.
Speed of darkness
Status: philosophical
Philosophically speaking, darkness is simply the absence of light, and their speeds should be the same. But it is worth thinking more carefully: darkness can take on a form that moves much faster. The name of this form is shadow. Imagine that you are pointing your fingers at the silhouette of a dog on the opposite wall. The beam from the flashlight diverges, and the shadow from your hand becomes much larger than the hand itself. The slightest movement of a finger is enough for the shadow from it on the wall to move a noticeable distance. What if we cast a shadow on the moon? Or to an imaginary screen even further?..
A barely perceptible wave - and she will run across at any speed that is given only by geometry, so no Einstein can tell her. However, it is better not to flirt with shadows, because they easily deceive us. It is worth going back to the beginning and remembering that darkness is simply the absence of light, so no physical object is transmitted during such a movement. There are no particles, no information, no deformations of space-time, there is only our illusion that this is a separate phenomenon. In the real world, no darkness can compare in speed with light.