?How do we know the speed of light
The speed of light, as we know it now, is about 300,000 km/sec
? How can we measure something moving at such an amazing speed
? Can you at that speed go around the planet seven and a half times in one second
What do you think, my dear reader, that you know that the beginning of these attempts to measure the speed of light was at a time when none of these current technologies,
? such as the laser measuring devices we have now, did not exist
? Even there was no electricity yet, isn't that strange
Attempts to measure the speed of light
In the early seventeenth century, the astronomer Galileo Galilei tried to measure the speed of light and did his famous experiment.
Galileo's experiment to measure the speed of light
Galileo sent two people, each carrying an ordinary lamp, and the distance between them was one mile, and Galileo asked them to give one to the other a light signal with his lamp.
Then Galileo calculated the time between one of them sending the signal and the other responding, taking into account the proportion of human error, to see that the difference was clear, which is the time it took for the light to travel the distance between them, which is, as we mentioned, a full mile, but the experiment failed unfortunately!
Reasons for the failure of Galileo's experiment
Light travels this simple distance in the experiment in one hundred thousandth of a second, which is a very small amount of time and can never be observed with the naked eye only.
As a result of that experiment, Galileo recorded that the speed of light is certainly too large to be determined by an experiment like this
And maybe 10 times faster than the speed of sound
Romer's experiment to measure the speed of light
About forty years after Galileo's experiments, another scientist named "Ole Romer" did another experiment, but this time it was very intelligent and accurate, as we will see shortly.
Oli Romer and Bradley Telescope
In the seventeenth century, sea voyages were at the height of their activity, but there was one of the problems that needed a radical solution, which was to agree on a unified timing for voyages that all sailors could agree on in the various coasts and seaports so that their voyages would be organized together and synchronized, and in this era there were no Hours after or any precise tools that enable them while they are sailing -in the sea- to measure time with an accuracy compatible with those on land. The use of the eclipses of the moons of Jupiter, and that eclipses are regularly and accurately and repeatedly in determining the time and agree that it is fixed for everyone
Determining the time using the eclipse
It was a great idea, and sailors at sea could use small telescopes on their ships, and determine the moment of entry of the largest moons of Jupiter, let it be - Io, for example - in the area of the eclipse precisely, but another problem appeared!
Lunar eclipse times
The scientist Ole Romer noticed that the dates of the eclipse of the moon of Jupiter change from the date calculated for it with the change in the distance of the Earth from Jupiter during their orbit around the sun; So that the difference in duration is determined by their distance from each other; That distance that increases when the Earth is as far as possible from Jupiter, and decreases when the Earth is as close as possible to Jupiter, and when the Earth is in the middle; The difference becomes a middle ground between the two accounts, so it is difficult for sailors to use that idea to determine their own timing system, so everyone neglected it, but "Romer" continued to monitor.
Romer determines the reason for the delay of the eclipse
Here, Romer came to a simple idea that says: Perhaps the problem is not in the movement of the moon "Io" or in the shadow of Jupiter, but the problem is that the light has a specific speed, and thus it takes longer to reach Earth when it is far from Jupiter, "Romer" made his equations But he made a mistake in calculating the change in time, so he recorded the speed of light as 200,000 kilometers per second, which is a huge difference indeed, but the “Romer” method itself is very accurate and with accurate calculations, the result is accurate, in any case we are 50 years away from more experience Accuracy.
locating stars
Parallax is an apparent change in the position of an object that we observe from afar.. This change is observed due to the change in our position on planet Earth as it rotates. Here is an example from the reality:
You see the sun at sunset, it is above the minaret of the town’s mosque, then when you move your car a few dozen meters and look again at the sun, you find it now above another building and left its first position.
When the Earth revolves around the sun in its path, the diameter of its orbit is about 300 million kilometers, and this transition in the orbit leads to a deviation of the positions of the stars and objects that we observe relative to another fixed point (another star for example).
starburst
When we observe a star during the summer and determine its location, and then during the winter we re-observe the same star, we will find that its position has changed or “displaced” from the previous position, and the closer this star is, the more clear its change of position or (displacement).
Bradley method for measuring the speed of light
In 1728, James Bradley, a British physicist, was observing the star "Gamma the Dragon" in the constellation of the Dragon. Note strange data in his measurements
During the observation, the star moved in the sky in a large oval with a diameter of 41 arc seconds; Rather, measurements of other groups of stars caused the same results, everyone moves in the same way, and the stars could not be so close or all of them next to each other.
An example of star movement
This is similar to when you are standing in the rain, you will direct the umbrella completely upwards in a vertical direction, but when you run, the rain will appear diagonally and not vertically, and you will direct the umbrella forward a little according to your running speed
From here you can calculate the degree of inclination of the canopy and measure the speed of the rain in relation to your running speed
Bradley kept thinking in confusion!! until he discovered during a trip in the Thames in southern England that the problem may not have anything to do with the issue of displacement and change of observational position, but the problem has to do with the speed of the Earth’s rotation itself and not the distance it traveled in its orbit around the sun
Simple example of movement and speed
To understand this, let's imagine that there is a train that stops when it rains. When you look out your window, you will find that the raindrops fall completely vertically, but when the train moves, you see the rain as if it falls diagonally and not vertically, and if the speed of the train increases, the apparent tendency of raindrops increases.
That - then - is what happens when we observe the stars in their movement, the light falling from them in a direction perpendicular to the earth does not appear vertically because the earth itself moves and moves in its orbit.
Reaching the speed of light
Here, the genius "Bradley", through the use of mathematics in trigonometry, was able to measure the angle of inclination of the beam of light coming from the observed star, and he was able to give a near-accurate estimate of the speed of light, and his calculations were 301 thousand kilometers per second!
Back to planet earth
Well, let's go back to Earth, the old Galileo experiment was correct in terms of method and steps, but the distance between the two people was very small.
Therefore, the vast distances between our planet Earth and the giant Jupiter enabled us, or we spotted some stars in the depths of space. The distances enabled us to measure the speed of light in an easier and more accurate way.
Vizo method for measuring the speed of light
By the nineteenth century AD, engines gave us a different opportunity to measure the speed of light, starting with "Armand Viseau," the French physicist.
The idea of FIZO was very effective, and it is summarized in the following experiment:
A powerful source of light emits a focused beam of light in the direction of a mirror at a distance of eight kilometers to reach a mirror and is reflected from it again and back to the source of its origin
On the way back to the reflected light beam we put a wheel with slots and frequent equal holes, this wheel rotates by a powerful motor, and during the return of the light beam it may pass through the holes of the revolving wheel and it may come across the solid part without slots from it and thus it will not return again to the source!
And here, "Fizo" adjusts the speed of the motor's rotation and the rotation of the perforated wheel so that the reflected light ray passes between one of the slots and reaches the mirror and then on its way back it passes through the slot next, here you can simply measure the distance between the two slots in the wheel and the speed of rewinding, and thus we can measure the speed of light Accurately, FIZO calculated it at 313 km/s, a difference of about 4% from the exact result.
Michaelson's method for measuring the speed of light
In a similar way, the American physicist Albert Michaelson in 1920 made very precise and important modifications to the FIZO experiment, adding - instead of a toothed wheel - an eight-sided mirror rotating at different speeds, at a distance of 35 km, to reflect the light ray from a source to a receiver on the opposite side, By calculating the speed of rotation of the mirror, Michaelson's team was able to measure the speed of light with a slight difference from its known value. He expected it to be 299,796 plus or minus 4 kilometers.
Measuring the speed of light at home
As for the modern picture of the speed of light, it developed because of the Second World War, with our need for accurate measurements that determine the speed of light so that we can adjust our radars, and send the codes to planes and submarines in the depths of the Atlantic. The center of those measurements was the experiment of British physicist Louise Aisen.
Louise Eisen's method for measuring the speed of light
Louise Aisen made stagnant waves by passing two microwaves of the same frequency and amplitude, but opposite in direction, within a specific area of 8 microns, and this experiment was able to determine an accurate reading of the speed of light of 299,792.5 km / h, in order to better understand Aisen's method. Perform the same experiment at home.
A home experiment to measure the speed of light
All you need is a microwave, remove the rotating plate from it, put in the microwave a long piece of chocolate, then rotate the device for one minute, what will happen is that the microwaves are stagnant waves, just vibrating up and down in the same place, in the nodes between the vibrations The wave energy is lowest, while it is highest in wave regions; So when you come out a piece of chocolate, you will find on its surface a group of points that have melted, and other points that have not started to melt yet.
Now calculate the distance between two molten points on the surface of a piece of chocolate, that's half the wavelength, a simple math can multiply that value by 2 to get a full wavelength, and then multiply that value by your device frequency - written in the background of each Device- You will get the speed of light very accurately, at home!
Perhaps after that last experience, the implicit goal of this article will become clear to you. At first glance, the topic of measuring the speed of light seems very difficult, and it requires very huge distances, but science always plays in indirect ways, the scientific method pushes us to devise different ways to circumvent what seems impossible to step down. The impossibility part aside, and you quote some light from the possible. In the “Vizo” experiment, for example, we switched the speed of light with the speed of rotation of the wheels, and in the Aisen experiment, we measured the length of one stagnant wave, and here we measure it through a piece of chocolate at home, just because there is a law that helps us to Turning difficult things into a lot easier, with great taste
And to another article.. you are well my friends
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