Every week we will delve deeper into a physical idea known in popular literature and bridge the gap between what is shown in the media and what science really states. This time we will start with wave-particle duality, an elusive concept that sometimes raises more questions than answers, but in truth has long ceased to worry scientists.
Until the beginning of the 20th century, physicists believed that the world was made of particles. For them, particles are elementary bodies that cannot be divided and are the building blocks of matter in the universe. For those particles to move in space they must be energetically charged. The particles can increase their energy reserve through gravitational attraction, light rays, or directly from electric and magnetic fields. Gravitational or electric attraction arises from a fundamental force in nature, but what about light? In those years, the scientific community recognized light as a wave object. Physicists defined the wave as a phenomenon that transports energy in a physical medium, therefore light necessarily transports energy in space. You don't need to be a physicist to recognize the fact that light carries energy, the heat of the sun is enough to understand this. Over the years, the wave definition expanded mainly after physicists realized that light does not need a medium to move - light is actually created as a wave in the electric and magnetic field, meaning it is simply a different expression of the electromagnetic force. At the same time, the fact that light behaves as a wave gives it special abilities - it can scatter, break, interfere and the strangest of all, it can pass through walls.
Particle or wave?
The wave concept of light was undermined in the twentieth century thanks to several discoveries, the first of which was published in 1905 by Albert Einstein in an article explaining the photoelectric effect. The ingenious idea behind it is actually quite old-fashioned. Contrary to the accepted view in the 20th century, Newton believed that light consists of a stream of particles. Einstein put the controversial idea on the photoelectric effect and published an article that won him the Nobel Prize. In this effect, light can strip electrons from a piece of metal and induce a measurable current. The surprising thing is that, contrary to the wave perception, the intensity of the current is affected by the frequency of the light. This observation stands in contrast to the classical idea that the energy is proportional only to the brightness of the light. In the photoelectric effect, electrons begin to be released only above a critical frequency. Above this frequency, the "bluer" the light, the more energetic the free electrons and the electric current increases (at the same time, more electrons are released with a higher probability). Because the current increases significantly with the change in frequency, Einstein realized that the structure of light is wrong and the missing piece of the puzzle is in the microscopic process that takes place between the light and the electron. In order for the electron to be released from the metal, it needs energy greater than the force that binds it to the material. If light is a wave, it's only a matter of time before the electron is released. If the light is made of particles, the electron, with the greatest probability, will swallow one dose of energy every time it comes into contact with the light particles (or in the accepted name - photons. Several doses are possible but with a very, very low probability). If the amount of energy is not enough for release, the light will be scattered instead of being absorbed. The explanation that the color of the light affects the electric current is because bluer colors (that is, towards the blue in the spectrum) are more energetic - the energy portion of the photon is proportional to the frequency it carries. The bluer the light, it increases the current because the energy absorbed by the electron is greater. At the same time, the illumination intensity releases more photons and increases the amount of electrons that detach from the metal (assuming that the energy is great enough to release the electron). Both processes increase the current but the threshold frequency is due to the particle nature of light and matter. If you feel confused by the tendency to sometimes think of light as a particle and sometimes as a wave, you are not alone. This is the essence of wave-particle duality. If only the connection to energy bothers you, the concept of "frequency" doesn't really matter, the main thing is that there is a way to energetically classify the light.
The material takes on wavy properties
The second observation came after the physicist de Broglie who extended the principle of duality to the particles of matter and attributed wave properties to them. If the energy of the light particle depends on the classical frequency, maybe the energy of the material particles dictates a characteristic frequency, or a certain wavelength? The de Broglie principle defines for physicists the energetic limit from which matter behaves as a wave, or in other words when quantum theory must be taken into account. It even explains why large bodies do not behave as waves. The more massive the bodies, the shorter the wavelength. For example, the typical wavelength of an average person is more or less equal to ten to the minus thirty-four meters, that is, one hundred billionth billionth billionth billionth of a billionth of a meter, infinitely small. For wave phenomena to be detected in nature, the characteristic wavelength should be more or less in the order of magnitude of the physical system. If it is smaller, wavy properties do not change and the body can be treated as a spatial object. De Broglie's principle is not just a fanciful idea of a scattered scientist, but an idea that has been confirmed over and over again in electron and heavier particle scattering experiments. In these experiments, scientists show that the electrons moving towards tiny slits create an interference pattern similar to light waves.
The modern interpretation of duality
So is light a wave or a particle? Do particles sometimes behave like waves and vice versa? The development of quantum mechanics deepened our understanding of the basic structures of nature and removed confusion. Let's start with the de Broglie principle - this principle implies a characteristic size called "wavelength". Despite the temptation, one should be careful not to assume that the particles of matter behave as waves just because we can calculate a wavelength similar to light. The picture became clearer when Schrödinger showed that the characteristic wavelength belongs to a "mathematical wave". In these terms, a wave is nothing more than a periodic solution to a differential equation (containing derivatives). The mathematical wave is actually a function that estimates the probability of the particle being at any point in space. If so, the accepted answer to the duality that popular scientific literature likes to cite is the one that Schrödinger or Heisenberg imparted to physicists - light and matter are particles whose movement in space is dictated by a wave that accompanies them (the wave is sometimes referred to as the wave function of the particle). The wave is not a measurable physical quantity but is influenced by the environment. At any point in space a certain height wave whose size dictates the probability of the particle being in that area. This answer is unsatisfactory in many ways, both mathematically and physically. The real answer was formulated with the advent of quantum field theory and is explained in modern scientific literature - the building blocks of nature are not particles, or waves, but fields from which waves are created. These waves have particle properties at low energy scales, but at large energy scales corrections arising from the quantum theory of the fields in nature must be taken into account. The union between the particles of matter and the particles of force into a uniform mathematical language (quantum field theory) is considered a sufficient solution to the paradox of duality, and therefore many of the books on quantum mechanics hardly devote chapters to this duality.
Each week I will dedicate an article to an idea or a common concept in modern physics. If you have suggestions or requests for this corner, you are welcome to contact me at the email address: Noamphysics@gmail.com
More of the topic in Hayadan:
16 תגובות
or by their common name - or by their common name
More energetic - more energetic
The picture became clearer as Schrödinger - The picture became clearer as Schrödinger
But fields on their backs create waves - but fields on their backs create waves (probably)
Light is not matter
And a wave is not something, a wave is something that something does
And by the way, electron and photon are also only theoretical particles
In short, Einstein was just an overrated moron
He never invented anything and never registered a single patent in his life.
His contribution to humanity is a theory that even after 100 years has not been proven to be impossible.
All these professors are idiots because they think that light is matter, or rather they don't think at all, they just gurgle the drawings in the book.
In my understanding, we can know the wavelength of a photon with any desired precision and therefore also its momentum.
Therefore according to the uncertainty principle, we cannot know the photon's position at all with any degree of accuracy, even though we know exactly the position of ct.
Let's move on to weaving. If we have two fully entwined electrons in the room, and one of them is measured at 2 and the other at 4, can we say that before the first was measured at 2 it did not have a quantum state (spin for example) and it was the measurement that determined its state? On the other hand, the second measured at 4 must have the opposite state which we know long before the measurement? Therefore we can say that the measurement of the first determined the quantum state of the second, but not the other way around.
It is said that we have two spaceships passing each other and in each of them a particle is intertwined with a particle in the other spaceship. At the moment of the suit, the clocks in the spacecraft show 0. In the first, the particle is measured by 3 times six times, and in the second by 5.
Will the spins be reversed in the particles?
Who can say that the first measurement at 3 determined the second measurement at 5 but not the other way around?
Lashfira -
The quantum field that describes the electroromantic fields A can be found in any configuration you choose with a certain probability according to Feynman, but the wave propagation of the measurable field E (electric) cannot be found outside the light cone (electric/magnetic wave equivalent to light). You can think of this as the trajectories of A forcing object E to zero out of the light cone.
Regarding the uncertainty - remember how we defined the measurement of light: we need to swallow it first to detect it. Once it is swallowed, its speed (and also its location to be honest) doesn't really matter because it no longer exists. In practice we claim that the photon is "there" when it is no longer there, but a fraction of a second ago it was around. To trace the propagation of light all we will have to measure is the time difference between the moment the photon left and the moment it met the particle. Regardless, classical or quantum, there will always be some uncertainty measured, there's nothing we can do, we can never measure anything with infinite precision.
What bothers me about the description of the photon located at a distance ct from the source is that the photon has a certain wavelength in a specific frame of reference and therefore also a certain momentum.
The uncertainty principle does not allow a quantum object to have both definite momentum and position, whether we measure them or not.
Thanks Noam.
Feynman in QED says that a quantum object, photon or electron, moves in all possible paths and the integral of all of them should be summed up. On the short path from the source to the background, the electron or photon also visits Andromeda.
I understand from your answer that for measurement purposes, a light beam behaves classically, and we cannot measure any interference outside the classical light cone. No measurement will give us a result at a distance greater than ct.
By the way, by DA do you mean Da Aka?
to Shapiro,
If I understand your questions, they can all be formulated in one question - can light be measured even outside its light cone? or at any other point not determined by ct. You have to be careful between interpretations you hear about quantum mechanics and those that really describe nature, especially relative nature like light. According to quantum field theory, the elementary quantities are in nature fields. Fields are non-local objects and can evolve in time also non-locally, but in the end we want to measure photons - to do this we need to measure electric and magnetic fields in space, not the quantum field known as A that creates them. Quantum calculations show that if we try to calculate the probability of an electric field that started at point C and ended at point D, the magnitude will differ from zero only if the measurements are made inside the light cone. No causality is broken and the quantum system behaves properly.
DA The fact that the photon or any other particle can be found effectively in several places in space, does not mean that the probability is the same everywhere in space, it can change everywhere and still allow the stochastic nature of quantum mechanics to exist.
Thank you Noam. I will try to simplify the question.
I look at the clock, when it shows 07.00.00 I press my green laser button which points in the direction of Mars which is for the purpose of the example one light hour away from me.
Along the road, which is an hour long, there are scattered clocks that have been synchronized in advance, as Einstein suggested in his speech about synchronized clocks throughout space.
Questions:
1. Is the question well defined?
2. After a minute, are photons from my laser also halfway to Mars?
3. A monochromatic green photon has a definite frequency in a given reference frame. Doesn't the uncertainty principle rule out a precise location for the photon, and actually forces it to be spread with equal probability throughout space as Feynman says? After all, the square of the probability wave is the chance of finding a quantum particle at a certain point.
4. In practice, can photons emitted from an ordinary flashlight at moment 0 be found after a minute at a light-hour distance from the flashlight, or are they all located at a distance ct from it?
Thanks.
Israel Shapira,
First of all, thanks for the comment - corrected.
Regarding your questions - I am not sure about the synchronization of the clocks on Mars and on Earth. To create synchronized clocks you need to create them in the same place but as soon as they disconnect they go out of sync. Even if they were at the same moment on Mars and on Earth at the same time (a somewhat strange term to say 'moment' because the events are not the same) they go out of sync immediately afterwards due to the effect of gravity and distance. But let's put that aside for a moment.
The wave function of light is an elusive concept - quantum mechanics is not relativistic and therefore there is no equivalent Schrödinger equation for a photon as there is for a particle. This does not mean that they did not try all kinds of methods to circumvent this, one of them is to ask what is the probability that a photon will be swallowed by a particle - once a photon is swallowed, its position just before the swallowing is known. The idea fits with experimental physics because we need to use certain tools that absorb the light to detect it. This probability is determined directly from solutions of Maxwell's equations, or in other words from the classical electric and magnetic field. Therefore, in a certain sense, some attribute the classical wave equation of light to the "wave function of the photon". This description is also compatible if we include special relativity in the game, that is, when quantum field theory is taken into account. DA According to this Torah there is no law that determines the conservation of the number of photons in the universe. They can completely disappear from the world or significantly increase their number. Therefore the description of light in field theory is the same for a single particle or many particles. Of course, the two situations can be distinguished, but the mathematics of both cases derives from the quantum description of the electromagnetic fields.
Another point - if the McQueal equation can be analogous to the wave function, then there is no single function for light because there are many solutions. This is also classically true. Light can be concentrated in a bundle of waves around a specific location like a laser, or be spread widely in space.
Thank you Noam for the interesting article.
Einstein's photon paper was in 1905, wasn't it? It says 1909..
You have a question that has been asked here before and has not yet been properly answered.
We have two synchronized clocks, one in Israel and the other in Mars. The distance between them for the purpose of the example - a light hour.
All the way between Israel and Mars, clocks are also synchronized.
At moment 0 on earth clock, I press the button of the device that launches a single green photon towards Mars. The photon reaches Mars in exactly one hour according to the Mars clock. No measurement is performed during the entire course of the experiment.
Questions:
1. Can we say that in one minute according to the clock in the center of the road, the photon is not in its vicinity?
2. We know that we can always find the photon at a distance ct from the earth, but can we say that the photon is spread with equal probability along the entire length of the track during the time of the experiment (hour)? If not, is there a certain probability distribution for finding the photon? The classical answer is of course negative, but what is the quantum answer?
3. If the answer to 2 is positive and the photon is indeed applied with equal probability before the measurement, is this different for a photon beam? If instead of a single photon I light a flashlight in Israel at time 0, is the flashlight beam also spread with equal probability?
Thanks.
Everyone who reads the article does not know what material is?
Is the substance a quantitative concept? Like time for example, or the length of a line?
At this stage the material is a combination of letters, and each letter is a line scribble with a unique shape.
Physics deals with continuous quantitative things, such as line length, time, and energy
Matter is not a continuous quantitative thing.
Matter is a physical form, created by combining a quantity of passive time and energy.
Passive time is a quantitative physical concept, and energy is also a quantitative physical concept.
Passive time is absolute rest and absolute cold, and it fills the infinite space.
Passive time is the medium that transmits the light.
When matter is a physical form, the words wave and particle become a meaningless word.
א
I know from personal experience that a chemical substance can be injected into the body with a high level of precision through some kind of wave
to Daniel -
Let's start with what you correctly stated - it is correct to say that the bluer the light is, the more energetic it is and will give more kinetic energy to the electron after release, at the same time the intensity of illumination = more photons and therefore more electrons that are likely to be released, which means the current increases. But note the following notes:
Regarding the first sentence - this claim was given as an assumption that physicists in the past believed. At the end of the 19th century, physicists assumed that light behaves according to the mechanical wave theory, that is, the energy of the wave is proportional to its amplitude, (to the maximum height of the wave) and not to the frequency (to the color). The intensity of the illumination is equal to the increase of the amplitude. If the amplitude is greater, the energy per unit area that falls on the surface is greater, and therefore more energy falls on an electron. As a result of increasing the illumination intensity, the current increases. why? It is likely that more electrons will be released if the energy per unit area increases (note that not all electrons are equally strongly bound to the metal) and current is not only a function of the number of electrons, but also the speed of their movement. More energy thrown into the metal equates to more energetic electrons moving faster. The idea in the sentence is that no matter what the color of the illumination, more light = more current. Of course this is not true because it is not what is measured in the end, but it is a natural assumption that comes from wave theory. What you see is that even if we shine a bright red light, almost no current will be measured. Maybe "not always increases" is missing in the written sentence.
Regarding the second sentence - it is also fine because non-linear processes can occur and the electron can swallow with lower probabilities some less energetic photons and be released from the metal, even if a single photon is not energetic enough to release it. If the light is bluer, fewer photons are required for release, in other words the probability of release increases. As the probability increases, the number of electrons released increases and the current increases as well (remember, current is a function of the electron density and their speed).
Bluer light = greater probability of release = more electrons = more current.
Again I mention, not all electrons are bound to the same extent, and for some of them red light is enough for them to detach from the metal, and of course this can be measured.
In any case, I took note and refined the claims in the article.
"The surprising phenomenon is that, contrary to the wave perception, the intensity of illumination does not increase the intensity of the electric current"
This is of course a complete error, in fact every paragraph is completely wrong.
The frequency of the light affects the kinetic energy of the electrons, while the intensity of the light (the number of photons) affects the number of emitted particles (assuming, of course, that the frequency is high enough), that is, the intensity of the light certainly affects the current.
"The "bluer" the light is, it releases more electrons and increases the electric current" - not true, the greater the frequency of the light, the greater the kinetic energy of the electrons.
Nice initiative.
An interesting article from Monet:
https://m.ynet.co.il/articles/rk15j5d1y
I would be happy if there was an expansion on the subject here as well.
Thanks in advance.