What is the speed of light in air? Peculiar particles - photons

epigraph
The teacher asks: Children, what is the fastest thing in the world?
Tanechka says: The fastest word. I just said, you won’t come back.
Vanechka says: No, light is the fastest.
As soon as I pressed the switch, the room immediately became light.
And Vovochka objects: The fastest thing in the world is diarrhea.
I was once so impatient that I didn’t say a word
I didn’t have time to say anything or turn on the light.

Have you ever wondered why the speed of light is maximum, finite and constant in our Universe? This is a very interesting question, and right away, as a spoiler, I’ll give away the terrible secret of the answer to it - no one knows exactly why. The speed of light is taken, i.e. mentally accepted for a constant, and on this postulate, as well as on the idea that all inertial frames of reference are equal, Albert Einstein built his special theory of relativity, which has been pissing scientists off for a hundred years, allowing Einstein to stick his tongue out at the world with impunity and grin in his grave over the dimensions the pig that he planted on all of humanity.

But why, in fact, is it so constant, so maximum and so final, there is no answer, it’s just an axiom, i.e. a statement taken on faith, confirmed by observations and common sense, but not logically or mathematically deducible from anywhere. And it is quite likely that it is not so true, but no one has yet been able to refute it with any experience.

I have my own thoughts on this matter, more on them later, but for now, let’s keep it simple, on your fingers™ I’ll try to answer at least one part - what does the speed of light mean “constant”.

No, I won’t bore you with thought experiments about what would happen if you turn on the headlights in a rocket flying at the speed of light, etc., that’s a little off topic now.

If you look in a reference book or Wikipedia, the speed of light in a vacuum is defined as a fundamental physical constant that exactly equal to 299,792,458 m/s. Well, that is, roughly speaking, it will be about 300,000 km/s, but if exactly right- 299,792,458 meters per second.

It would seem, where does such accuracy come from? Any mathematical or physical constant, whatever, even Pi, even the base of the natural logarithm e, even the gravitational constant G, or Planck’s constant h, always contain some numbers after the decimal point. In Pi, about 5 trillion of these decimal places are currently known (although only the first 39 digits have any physical meaning), the gravitational constant is today defined as G ~ 6.67384(80)x10 -11, and the constant Plank h~ 6.62606957(29)x10 -34 .

The speed of light in vacuum is smooth 299,792,458 m/s, not a centimeter more, not a nanosecond less. Want to know where this accuracy comes from?

It all started as usual with the ancient Greeks. Science, as such, in the modern sense of the word, did not exist among them. The philosophers of ancient Greece were called philosophers because they first invented some crap in their heads, and then, using logical conclusions (and sometimes real physical experiments), they tried to prove or disprove it. However, the use of real-life physical measurements and phenomena was considered by them to be “second-class” evidence, which cannot be compared with first-class logical conclusions obtained directly from the head.

The first person to think about the existence of light's own speed is considered to be the philosopher Empidocles, who stated that light is movement, and movement must have speed. He was objected to by Aristotle, who argued that light is simply the presence of something in nature, and that’s all. And nothing is moving anywhere. But that's something else! Euclid and Ptolemy generally believed that light is emitted from our eyes, and then falls on objects, and therefore we see them. In short, the ancient Greeks were as stupid as they could until they were conquered by the same ancient Romans.

In the Middle Ages, most scientists continued to believe that the speed of propagation of light was infinite, among them were, say, Descartes, Kepler and Fermat.

But some, like Galileo, believed that light had speed and therefore could be measured. The experiment of Galileo, who lit a lamp and gave light to an assistant located several kilometers from Galileo, is widely known. Having seen the light, the assistant lit his lamp, and Galileo tried to measure the delay between these moments. Naturally, nothing worked for him, and in the end he was forced to write in his writings that if light has a speed, then it is extremely high and cannot be measured by human effort, and therefore can be considered infinite.

The first documented measurement of the speed of light is attributed to the Danish astronomer Olaf Roemer in 1676. By this year, astronomers, armed with the telescopes of that same Galileo, were actively observing the satellites of Jupiter and even calculated their rotation periods. Scientists have determined that the closest moon to Jupiter, Io, has a rotation period of approximately 42 hours. However, Roemer noticed that sometimes Io appears from behind Jupiter 11 minutes earlier than expected, and sometimes 11 minutes later. As it turned out, Io appears earlier in those periods when the Earth, rotating around the Sun, approaches Jupiter at a minimum distance, and lags behind by 11 minutes when the Earth is in the opposite place of the orbit, and therefore is further from Jupiter.

Stupidly dividing the diameter of the earth's orbit (and it was already more or less known in those days) by 22 minutes, Roemer received the speed of light 220,000 km/s, missing the true value by about a third.

In 1729, the English astronomer James Bradley, observing parallax(by a slight deviation in location) the star Etamin (Gamma Draconis) discovered the effect aberrations of light, i.e. a change in the position of the stars closest to us in the sky due to the movement of the Earth around the Sun.

From the effect of light aberration, discovered by Bradley, it can also be concluded that light has a finite speed of propagation, which Bradley seized on, calculating it to be approximately 301,000 km/s, which is already within 1% of the value known today.

This was followed by all the clarifying measurements by other scientists, but since it was believed that light is a wave, and a wave cannot propagate on its own, something needs to be “excited,” the idea of ​​the existence of a “luminiferous ether” arose, the discovery of which the American failed miserably physicist Albert Michelson. He did not discover any luminiferous ether, but in 1879 he clarified the speed of light to 299,910±50 km/s.

Around the same time, Maxwell published his theory of electromagnetism, which means that the speed of light became possible not only to directly measure, but also to derive from the values ​​of electrical and magnetic permeability, which was done by clarifying the value of the speed of light to 299,788 km/s in 1907.

Finally, Einstein declared that the speed of light in a vacuum is a constant and does not depend on anything at all. On the contrary, everything else - adding velocities and finding the correct reference systems, the effects of time dilation and changes in distances when moving at high speeds and many other relativistic effects depend on the speed of light (because it is included in all formulas as a constant). In short, everything in the world is relative, and the speed of light is the quantity relative to which all other things in our world are relative. Here, perhaps, we should give the palm to Lorentz, but let’s not be mercantile, Einstein is Einstein.

The exact determination of the value of this constant continued throughout the 20th century, with each decade scientists found more and more numbers after decimal point at the speed of light, until vague suspicions began to arise in their heads.

Determining more and more accurately how many meters light travels in a vacuum per second, scientists began to wonder what we are measuring in meters? After all, in the end, a meter is just the length of some platinum-iridium stick that someone forgot in some museum near Paris!

And at first the idea of ​​​​introducing a standard meter seemed great. In order not to suffer with yards, feet and other oblique fathoms, the French in 1791 decided to take as a standard measure of length one ten-millionth of the distance from the North Pole to the equator along the meridian passing through Paris. They measured this distance with the accuracy available at that time, cast a stick from a platinum-iridium (more precisely, first brass, then platinum, and then platinum-iridium) alloy and put it in this very Parisian Chamber of Weights and Measures as a sample. The further we go, the more it turns out that the earth's surface is changing, the continents are deforming, the meridians are shifting, and by one ten-millionth part they have forgotten, and began to count as a meter the length of the stick that lies in the crystal coffin of the Parisian "mausoleum."

Such idolatry does not suit a real scientist, this is not Red Square (!), and in 1960 it was decided to simplify the concept of the meter to a completely obvious definition - the meter is exactly equal to 1,650,763.73 wavelengths emitted by the transition of electrons between the energy levels 2p10 and 5d5 of the unexcited isotope of the element Krypton-86 in a vacuum. Well, how much more clear?

This went on for 23 years, while the speed of light in a vacuum was measured with increasing accuracy, until in 1983, finally, even the most stubborn retrogrades realized that the speed of light is the most accurate and ideal constant, and not some kind of isotope of krypton. And it was decided to turn everything upside down (more precisely, if you think about it, it was decided to turn everything back upside down), now the speed of light With is a true constant, and a meter is the distance that light travels in a vacuum in (1/299,792,458) seconds.

The real value of the speed of light continues to be clarified today, but what is interesting is that with each new experiment, scientists do not clarify the speed of light, but the true length of the meter. And the more accurately the speed of light is found in the coming decades, the more accurate the meter we will eventually get.

And not vice versa.

Well, now let's get back to our sheep. Why is the speed of light in the vacuum of our Universe maximum, finite and constant? This is how I understand it.

Everyone knows that the speed of sound in metal, and in almost any solid body, is much higher than the speed of sound in air. This is very easy to check; just put your ear to the rail, and you will be able to hear the sounds of an approaching train much earlier than through the air. Why is that? It is obvious that the sound is essentially the same, and the speed of its propagation depends on the medium, on the configuration of the molecules from which this medium consists, on its density, on the parameters of its crystal lattice - in short, on the current state of the medium through which the sound transmitted.

And although the idea of ​​luminiferous ether has long been abandoned, the vacuum through which electromagnetic waves propagate is not absolutely absolute nothing, no matter how empty it may seem to us.

I understand that the analogy is somewhat far-fetched, but that’s true on your fingers™ same! Precisely as an accessible analogy, and in no way as a direct transition from one set of physical laws to others, I only ask you to imagine that the speed of propagation of electromagnetic (and in general, any, including gluon and gravitational) vibrations, just as the speed of sound in steel is “sewn into” the rail. From here we dance.

UPD: By the way, I invite “readers with an asterisk” to imagine whether the speed of light remains constant in a “difficult vacuum.” For example, it is believed that at energies of the order of temperature 10–30 K, the vacuum stops simply boiling with virtual particles, and begins to “boil away,” i.e. the fabric of space falls to pieces, Planck quantities blur and lose their physical meaning, etc. Would the speed of light in such a vacuum still be equal to c, or will this mark the beginning of a new theory of “relativistic vacuum” with corrections like Lorentz coefficients at extreme speeds? I don't know, I don't know, time will tell...

The speed of light is the distance that light travels per unit time. This value depends on the substance in which the light propagates.

In a vacuum, the speed of light is 299,792,458 m/s. This is the highest speed that can be achieved. When solving problems that do not require special accuracy, this value is taken equal to 300,000,000 m/s. It is assumed that all types of electromagnetic radiation propagate in a vacuum at the speed of light: radio waves, infrared radiation, visible light, ultraviolet radiation, x-rays, gamma radiation. It is designated by a letter With .

How was the speed of light determined?

In ancient times, scientists believed that the speed of light was infinite. Later, discussions on this issue began among scientists. Kepler, Descartes and Fermat agreed with the opinion of ancient scientists. And Galileo and Hooke believed that, although the speed of light is very high, it still has a finite value.

Galileo Galilei

One of the first to try to measure the speed of light was the Italian scientist Galileo Galilei. During the experiment, he and his assistant were on different hills. Galileo opened the shutter on his lantern. At the moment when the assistant saw this light, he had to do the same actions with his lantern. The time it took for the light to travel from Galileo to the assistant and back turned out to be so short that Galileo realized that the speed of light is very high, and it is impossible to measure it at such a short distance, since light travels almost instantly. And the time he recorded only shows the speed of a person’s reaction.

The speed of light was first determined in 1676 by the Danish astronomer Olaf Roemer using astronomical distances. Using a telescope to observe the eclipse of Jupiter's moon Io, he discovered that as the Earth moves away from Jupiter, each subsequent eclipse occurs later than calculated. The maximum delay, when the Earth moves to the other side of the Sun and moves away from Jupiter at a distance equal to the diameter of the Earth's orbit, is 22 hours. Although the exact diameter of the Earth was not known at that time, the scientist divided its approximate value by 22 hours and obtained a value of about 220,000 km/s.

Olaf Roemer

The result obtained by Roemer caused distrust among scientists. But in 1849, the French physicist Armand Hippolyte Louis Fizeau measured the speed of light using the rotating shutter method. In his experiment, light from a source passed between the teeth of a rotating wheel and was directed onto a mirror. Reflected from him, he returned back. The speed of rotation of the wheel increased. When it reached a certain value, the beam reflected from the mirror was delayed by a moving tooth, and the observer did not see anything at that moment.

Fizeau's experience

Fizeau calculated the speed of light as follows. The light goes its way L from the wheel to the mirror in a time equal to t 1 = 2L/c . The time it takes for the wheel to turn ½ slot is t 2 = T/2N , Where T - period of wheel rotation, N - number of teeth. Rotation frequency v = 1/T . The moment when the observer does not see light occurs when t 1 = t 2 . From here we get the formula for determining the speed of light:

c = 4LNv

Having carried out calculations using this formula, Fizeau determined that With = 313,000,000 m/s. This result was much more accurate.

Armand Hippolyte Louis Fizeau

In 1838, French physicist and astronomer Dominique François Jean Arago proposed using the rotating mirror method to calculate the speed of light. This idea was put into practice by the French physicist, mechanic and astronomer Jean Bernard Leon Foucault, who in 1862 obtained the value of the speed of light (298,000,000±500,000) m/s.

Dominique Francois Jean Arago

In 1891, the result of the American astronomer Simon Newcome turned out to be an order of magnitude more accurate than Foucault’s result. As a result of his calculations With = (99,810,000±50,000) m/s.

Research by the American physicist Albert Abraham Michelson, who used a setup with a rotating octagonal mirror, made it possible to determine the speed of light even more accurately. In 1926, the scientist measured the time it took light to travel the distance between the tops of two mountains, equal to 35.4 km, and obtained With = (299,796,000±4,000) m/s.

The most accurate measurement was carried out in 1975. In the same year, the General Conference on Weights and Measures recommended that the speed of light be considered equal to 299,792,458 ± 1.2 m/s.

What does the speed of light depend on?

The speed of light in a vacuum does not depend on either the frame of reference or the position of the observer. It remains constant, equal to 299,792,458 ± 1.2 m/s. But in various transparent media this speed will be lower than its speed in vacuum. Any transparent medium has an optical density. And the higher it is, the slower the speed of light propagates in it. For example, the speed of light in air is higher than its speed in water, and in pure optical glass it is less than in water.

If light moves from a less dense medium to a denser one, its speed decreases. And if the transition occurs from a more dense medium to a less dense one, then the speed, on the contrary, increases. This explains why the light beam is deflected at the transition boundary between two media.

The work of our subconscious

Our consciousness, which we sometimes consider our “I,” is only a small part of the work of the brain as a whole. Awareness of oneself as a person is only a small part of the brain’s work; most other processes occurring in the head are processed without the involvement of consciousness. These are not only automated reactions such as breathing, controlling the heart, muscles when walking, but also more complex ones: pattern recognition, the formation of a three-dimensional surrounding reality. The brain, in fact, at a preliminary level chooses what to show to consciousness and what to omit. Some actions are performed so automatically that the consciousness is not notified of the work being performed.

Quite by accident, I recently found out that I have published new books: “Conscious exits from the body. Experience of traveling to other worlds" and "Controlled dreams. Controlled reality." They came out from a certain publishing house IPL in 2016. It turns out that this also happens, the author himself does not know that he has new books coming out.

They renamed the book in their own way and released it as a new product from the author. I have no idea what kind of publishing house this is, but after reading the reviews of the books, we can conclude: this is my first and second book published by the Ves publishing house under the titles: “Wanderer of Dreams. Part 1. The beginning of the journey" and "Wanderer of dreams. Part 2. New Millennium.”

Essentially these are the same books. If you have previously read the Dream Traveler series, then there is no point in buying new books.

Why do you dream about rats?

So, to find out from which side to expect a rat bite, analyze your dream.

Let's sort it out how a thought can have power. How thoughts can generally interact with the universe, cause events not related to our direct actions. What laws of the universe allow us to fulfill our mental desires. How can our brain have the gift of seeing at a distance or sensing events happening somewhere far away that we have no idea about.

Let's assume that our body, and our brain in particular, is a machine. Complex, to some extent incomprehensible, but still a device that perceives and transmits signals to the outside. Let's make another assumption that we are somewhat similar to a modern computer. Lately, our brains have been compared more and more to electronic devices, so we will not deviate from this tradition. Thus, our thoughts are a kind of program, with cycles and functions that perform certain tasks. Some thoughts are initial data, but some have power - these are programs built according to the laws of the universe.

Over the past month I have encountered several people trying to change their past. Then someone talked about memories of a non-existent past.

Most people believe that changing the past is impossible, and there is no exact description of how to change the past. But, one way or another, I come across mysterious stories that cannot be confirmed or refuted. Any change in the past leads to everyone around remembering a new story. Thus, we cannot confidently say that such a story is not the author’s invention. Only some individuals retain memories of an alternate present. Sometimes it’s not even a memory, but only a feeling of the wrongness of the current moment; sometimes there are flashes of déjà vu, or false memories in the head of some moments that never actually happened, but for some reason are stored in the memory as memories.

The topic of how to measure, as well as what the speed of light is, has interested scientists since ancient times. This is a very fascinating topic, which from time immemorial has been the object of scientific debate. It is believed that such a speed is finite, unattainable and constant. It is unattainable and constant, like infinity. At the same time, it is finite. It turns out to be an interesting physical and mathematical puzzle. There is one option for solving this problem. After all, the speed of light was still measured.

In ancient times, thinkers believed that speed of light- this is an infinite quantity. The first estimate of this indicator was given in 1676. Olaf Roemer. According to his calculations, the speed of light was approximately 220 thousand km/s. This was not an entirely accurate value, but close to the true one.

Finitude and the estimate of the speed of light were confirmed half a century later.

In the future, the scientist Fizeau It was possible to determine the speed of light from the time it took the beam to travel an exact distance.

He conducted an experiment (see figure), during which a beam of light departed from the source S, was reflected by mirror 3, interrupted by toothed disk 2 and passed the base (8 km). Then it was reflected by mirror 1 and returned to the disk. The light fell into the gap between the teeth and could be observed through eyepiece 4. The time it took the beam to travel through the base was determined depending on the rotation speed of the disk. The value obtained by Fizeau was: c = 313300 km/s.

The speed of beam propagation in any particular medium is less than this speed in a vacuum. In addition, for different substances this indicator takes on different values. After few years Foucault replaced the disk with a rapidly rotating mirror. The followers of these scientists repeatedly used their methods and research designs.

Lenses are the basis of optical instruments. Do you know how it is calculated? You can find out by reading one of our articles.

You can find information about how to set up an optical sight consisting of such lenses. Read our material and you will not have any questions on the topic.

What is the speed of light in a vacuum?

The most accurate measurement of the speed of light shows the figure 1,079,252,848.8 kilometers per hour or 299,792,458 m/s. This figure is only valid for conditions created in a vacuum.

But to solve problems, the indicator is usually used 300,000,000 m/s. In a vacuum, the speed of light in Planck units is 1. Thus, light energy travels 1 Planck unit of length in 1 unit of Planck time. If a vacuum is created in natural conditions, then X-rays, light waves in the visible spectrum and gravitational waves can travel at such speeds.

There is a clear opinion among scientists that particles with mass can take on a speed that is as close as possible to the speed of light. But they are not able to achieve and exceed the indicator. The highest speed, close to the speed of light, was recorded during the study of cosmic rays and during the acceleration of certain particles in accelerators.

The speed of light in any medium depends on the refractive index of this medium.

This indicator may be different for different frequencies. Accurate measurement of the quantity is important for the calculation of other physical parameters. For example, to determine the distance during the passage of light or radio signals in optical ranging, radar, light ranging and other areas.

Modern scientists use different methods to determine the speed of light. Some experts use astronomical methods, as well as measurement methods using experimental technology. The improved Fizeau method is very often used. In this case, the gear wheel is replaced with a light modulator, which weakens or interrupts the light beam. The receiver here is a photoelectric multiplier or photocell. The light source can be a laser, which helps reduce measurement error. Determination of the speed of light According to the time of passage of the base, it can be done using direct or indirect methods, which also allow one to obtain accurate results.

What formulas are used to calculate the speed of light?

1. The speed of light propagation in a vacuum is an absolute value. Physicists denote it with the letter “c”. This is a fundamental and constant value that does not depend on the choice of reporting system and characterizes time and space as a whole. Scientists assume that this speed is the maximum speed of particle movement.

   Speed ​​of light formula in a vacuum:

   s = 3 * 10^8 = 299792458 m/s

   here c is an indicator of the speed of light in vacuum.

2. Scientists have proven that speed of light in air almost coincides with the speed of light in vacuum. It can be calculated using the formula:

The speed of light is the absolute value of the speed of propagation of electromagnetic waves in a vacuum. In physics, it is traditionally denoted by the Latin letter “c” (pronounced [tse]). The speed of light in a vacuum is a fundamental constant that does not depend on the choice of inertial reference frame (IFR). It refers to the fundamental physical constants that characterize not just individual bodies, but the properties of space-time as a whole. According to modern concepts, the speed of light in a vacuum is the maximum speed of particle movement and the propagation of interactions. Also important is the fact that this value is absolute. This is one of the postulates of SRT.

In a vacuum (emptiness)

In 1977, it was possible to calculate the approximate speed of light equal to 299,792,458 ± 1.2 m/s, calculated based on the 1960 standard meter. It is currently believed that the speed of light in a vacuum is a fundamental physical constant, by definition exactly equal to 299,792,458 m/s, or approximately 1,079,252,848.8 km/h. The exact value is due to the fact that since 1983, the standard meter has been taken to be the distance that light travels in a vacuum in a period of time equal to 1/299,792,458 seconds. The speed of light is symbolized by the letter c.

Michelson's experiment, fundamental to SRT, showed that the speed of light in a vacuum does not depend either on the speed of the light source or on the speed of the observer. In nature, the following propagate at the speed of light:

actual visible light

other types of electromagnetic radiation (radio waves, x-rays, etc.)

From the special theory of relativity it follows that the acceleration of particles with rest mass to the speed of light is impossible, since this event would violate the fundamental principle of causality. That is, it is excluded that the signal exceeds the speed of light, or the movement of mass at such a speed. However, the theory does not exclude the movement of particles in space-time at superluminal speeds. Hypothetical particles moving at superluminal speeds are called tachyons. Mathematically, tachyons easily fit into the Lorentz transformation - they are particles with imaginary mass. The higher the speed of these particles, the less energy they carry, and vice versa, the closer their speed is to the speed of light, the greater their energy - just like the energy of ordinary particles, the energy of tachyons tends to infinity as they approach the speed of light. This is the most obvious consequence of the Lorentz transformation, which does not allow a particle to accelerate to the speed of light - it is simply impossible to impart an infinite amount of energy to a particle. It should be understood that, firstly, tachyons are a class of particles, and not just one type of particle, and, secondly, no physical interaction can propagate faster than the speed of light. It follows from this that tachyons do not violate the principle of causality - they do not interact with ordinary particles in any way, and the difference in their speeds between themselves is also not equal to the speed of light.

Ordinary particles that move slower than light are called tardyons. Tardions cannot reach the speed of light, but only come as close as possible to it, since in this case their energy becomes unlimitedly large. All tardyons have rest mass, unlike massless photons and gravitons, which always move at the speed of light.

In Planck units, the speed of light in a vacuum is 1, that is, light travels 1 unit of Planck length per unit of Planck time.

In a transparent environment

The speed of light in a transparent medium is the speed at which light travels in a medium other than a vacuum. In a medium with dispersion, phase and group velocities are distinguished.

Phase velocity relates the frequency and wavelength of monochromatic light in a medium (λ=c/ν). This speed is usually (but not necessarily) less than c. The ratio of the phase speed of light in a vacuum to the speed of light in a medium is called the refractive index of the medium. The group speed of light in an equilibrium medium is always less than c. However, in nonequilibrium media it can exceed c. In this case, however, the leading edge of the pulse still moves at a speed not exceeding the speed of light in vacuum.

Armand Hippolyte Louis Fizeau experimentally proved that the movement of a medium relative to a light beam is also capable of influencing the speed of propagation of light in this medium.

Negation of the postulate about the maximum speed of light

In recent years, reports have often appeared that in so-called quantum teleportation, interaction propagates faster than the speed of light. For example, on August 15, 2008, the research group of Dr. Nicolas Gisin from the University of Geneva, studying bound photon states separated by 18 km in space, allegedly showed that “interactions between particles occur at a speed approximately one hundred thousand times greater than the speed of Sveta". Previously, the so-called Hartmann paradox - superluminal speed with the tunnel effect - was also discussed.

A scientific analysis of the significance of these and similar results shows that they fundamentally cannot be used for superluminal transmission of any signal or movement of matter.

History of light speed measurements

Ancient scientists, with rare exceptions, considered the speed of light to be infinite. In modern times this issue became the subject of debate. Galileo and Hooke admitted that it was finite, although very large, while Kepler, Descartes and Fermat still defended the infinity of the speed of light.

The first estimate of the speed of light was given by Olaf Roemer (1676). He noticed that when the Earth and Jupiter are on opposite sides of the Sun, eclipses of Jupiter's satellite Io are delayed by 22 minutes compared to calculations. From this he obtained a value for the speed of light of about 220,000 km/sec - inaccurate, but close to the true one. Half a century later, the discovery of aberration made it possible to confirm the finiteness of the speed of light and refine its assessment.