The speed of light: what is it and how was it measured?

The data presented below and the examples given do not claim to be absolute scientific accuracy, but are intended to explain to the reader in the simplest possible language the main and most interesting facts regarding the speed of light.

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What is the speed of light and how is it measured

Curiously, the speed of light was considered endless until the second half of the 17th century, that is, such great scientists as Johannes Kepler or Rene Descartes, for example, perceived it in this way. Only in 1676, the Danish astronomer Olaf Remer, who observed the eclipses of Jupiter’s moon Io, noticed that they do not coincide with the calculated ones in time and this discrepancy depends on the distance between the event and the observer. Taking into account the position of the Earth in its orbit relative to Jupiter, Roemer calculated the speed of light to be 220,000 km/s (mistaken by ~80,000 km/s).

At the beginning of the 19th century, scientists measured the speed of light using a practical “interruption method” and by 1950 they had achieved a result of 299,793.1 km / s with an error of 0.25 km / s, and the invention of the laser later made it possible to reach the limit of accuracy and fix the speed of light by mark 299 792 458 m/s with an error of 1.2 m/s.

Further refinement of one of the basic quantities of the theory of relativity became impossible due to the lack of an accurate definition of the meter – at that time it was equal to the length of a metal stick, which was the standard and stored in Paris. The issue was only resolved in 1983, when the General Conference on Weights and Measures redefined the meter as the distance traveled by light in 1/299,792,458 of a second. Accordingly, the speed of light became officially equal to 299 792 458 meters per second (or roughly: 300,000 km/s).

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What is the fundamentality of the speed of light

In fact, modern science knows only a few objective fundamental constants that remain unchanged. under any conditions. The speed of light does not depend on the observer, nor on the method of measurement, nor on time – it is really constant.

To prove the opposite, one can, for example, pass a beam of light through a complex inhomogeneous medium and it will pass through it much more slowly than through a vacuum. However, upon careful consideration of the experimental conditions, it turns out that the photons were moving at the same speed of light, but along a more complex trajectory.

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Why can’t anything overcome the speed of light?

If you create or discover an object that has a non-zero mass or has the property of interacting with other particles in some way, then you will invent time Machine. Nothing like this has ever been seen in the known world. Simplifying the scientific language, we describe the situation as follows:

Imagine events X and Y, where event X is the cause of event Y, and Y, respectively, is a consequence of X. For example, event X is a supernova explosion in a distant galaxy, and Y is the detection of its particles by astronomers on Earth. If the distance between X and Y is greater than the time between them (T) times the speed of light (C), then in different frames of reference we get three different results:

1. Event X happened before event Y;
2. Event Y happened before event X;
3. Events X and Y happened at the same time.

Obviously, the last two options are hardly possible from the point of view of modern science, which means that nothing can move or transmit information faster than the speed of light.

However, what about this situation: you take a very powerful flashlight, point it at Mars, and move your finger in a beam of light – if you do this fast enough, then the shadow from your finger “runs” on the surface of Mars faster than the speed of light, which refutes our theory.

Not really. The movement of the shadow cannot be called the movement of an object with mass, just as the shadow itself does not interact with anything, but is only the absence of light. Photons from your flashlight will reach Mars at the speed we already know of 299,792,458 meters per second.

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near-light speed

According to the postulates of the general theory of relativity, the faster we accelerate a particle with a certain mass, the more energy we need for this. At the same time, as it approaches the speed of light, this energy will tend to infinity.

However, this does not mean at all that light is orders of magnitude faster than anything else in the universe. For example, CERN scientists accelerated protons at the Large Hadron Collider to a speed of 299,792,455 m/s, which is only 3 m/s behind the weightless photons of light.

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FTL

The limitations described above, which modern physics imposes on speeds in the Universe, do not apply to particles that have no mass, do not interact with ordinary particles, and can travel faster than the speed of light. Such particles are usually called tachyons and at the moment their existence is only an assumption (it is difficult to come up with an effective tool for detecting them, because they do not interact with anything).

Another popular example of superluminal speed is quantum mechanical phenomena. At the very moment when you put one sock on your right foot, the second instantly and automatically became left, regardless of the distance between them. Approximately according to this principle, quantum communication is carried out when measuring the spin of photons, while information is not transmitted, however, in fact, one state passes into another without direct interaction between objects.

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The speed of light is visual

Astrophysicists in most cases are deprived of the opportunity to conduct full-fledged experiments in laboratories, as, for example, biologists or chemists do, due to the scale of the processes under study. At the same time, each astronomer has access to the largest test site, where grandiose tests are constantly taking place – this is the entire observable Universe with quasars, radio pulsars, black holes and other curious objects.

However, the most interesting astrophysical discoveries these days look like obscure complex graphs, and the public is forced to be content with processed images of only a few instruments, such as the Hubble telescope. Nevertheless, official science is now aware of the importance of media activities and is trying in every possible way to visualize for the layman processes that cannot simply be imagined in the head.

For example, NASA employee James O’Donoghue demonstrated the speed of light relative to our planet (eliminating the influence of the atmosphere in his calculations) – a beam of light circles the Earth 7.5 times in just one second, each time overcoming more than 40 thousand kilometers.

The distance to the Moon is about 384,000 kilometers (depending on the current location of objects) and photons will need 1.22 seconds to overcome it.

When transmitting data from Mars to Earth at the speed of light, at the moment of closest approach of the planets, you will have to wait more than six minutes, and at an average distance, the waiting time will drag on to half an hour.

At the same time, an average of 254 million km separates us from the “red planet”, the New Horizons probe, for example, has already flown away from the Earth by 6.64 billion km, and to get to the nearest planet not in the solar system, you need to fly 39.7 trillion km .

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