Our Mathematical Universe book -- Since when does light contain voltage?

[sevensages]

TL;DR

How is it possible for a beam of light to contain voltage?

I am currently reading Max Tegmark's book Our Mathematical Universe. Some of you are probably familiar with this book.

On page 167, Tegmark wrote the following: "It's not only 'stuff' that's made of Lego-like building blocks. As we mentioned in Part I of this book, so is light, being composed of particles called photons, inferred by Einstein in 1905.

Four decades earlier, James Clerk Maxwell had discovered that light is an electromagnetic wave, a type of electrical disturbance. If you could carefully measure the voltage between two points in a beam of light, you'd find that it oscillates over time; the frequency f of this oscillation (how many times per second it oscillates) determines the color of the light, and the strength of oscillation ( the maximum number of volts you measure) determines the intensity of the light."

It's my understanding that a beam of light is an electromagnetic wave of photons (and only photons) with no electrons. All my life I have always thought that electricity comes from a flow of electrons (and only electrons) with no photons. So I have always thought that a beam of light would have zero voltage because I thought that there is no electricity in a beam of light. Now I am aware of the fact that the letters "electro" in electromagnetic wave sounds like an abbreviation of the word electricity. But I have still always thought that there is no electricity in a beam of light because a beam of light is a wave of photons, not electrons.

Do beams of light have voltage? If so, assuming that only photons and not electrons are in a beam of light, how can a beam of light have voltage?

P.S. I am just a trucker. I am not a physicist or an engineer like many of you people. So please be gentle and don't chastise me for not knowing something that might seem very elementary to you.

 

[Ibix]

Yes, in principle you can use the electric component of light to push a current on a circuit. Light oscillates too fast for us to do this with current technology, but it's basically how radio antennas work. Crudely, you make a straight piece of wire, and the electrons oscillate because they are pushed by the radio wave, and you use some electronics to isolate and amplify the frequency of oscillation you want.

You seem to be mixing up charged particles (including, but not only, electrons) which are sources of the electromagnetic field, with photons which are disturbances in the electromagnetic field. It's like the difference between a stone thrown into a pond (the source of the ripples but not itself a ripple) and the ripples.

I would also add that describing a light pulse as "a wave of photons" may be mixing up classical and quantum physics, which will end in tears. It's an electromagnetic wave (classically) or a bunch of photons (in quantum theory - note that there are a lot of caveats and subtleties here, and photons are almost certainly not what you think they are).

 

[sevensages]

Your explanation went over my head to some degree. My interpretation of what you wrote is that you are saying "Yes, beams of light have voltage."

You seem to be mixing up charged particles (including, but not only, electrons) which are sources of the electromagnetic field, with photons which are disturbances in the electromagnetic field. It's like the difference between a stone thrown into a pond (the source of the ripples but not itself a ripple) and the ripples.

What if the source of the beam of light is the Sun? If the beam of light is sunlight, is the source of the beam of light still charged particles?

I would also add that describing a light pulse as "a wave of photons" may be mixing up classical and quantum physics, which will end in tears. It's an electromagnetic wave (classically) or a bunch of photons (in quantum theory - note that there are a lot of cabeats and subtleties here, and photons are almost certainly not what you think they are).

I think that photons are subatomic particles that make light. How is my understanding of photons wrong?

 

[berkeman]

My interpretation of what you wrote is that you are saying "Yes, beams of light have voltage."

Light waves have E and B components. The oscillating E-field component is what accelerates electrons in antennas and other metal structures that the EM wave passes through/around. Does that sound familiar?

https://en.wikipedia.org/wiki/Electromagnetic_radiation

 

[sevensages]

Light waves have E and B components. The oscillating E-field component is what accelerates electrons in antennas and other metal structures that the EM wave passes through/around. Does that sound familiar?

https://en.wikipedia.org/wiki/Electromagnetic_radiation

View attachment 371981

No. It does not sound familiar. You are probably a physicist or an engineer. My only physics training is an Physics class that I took in high school over a quarter of a century ago.

Do electrons travel on those electromagnetic fields?

 

[Baluncore]

Do beams of light have voltage? If so, assuming that only photons and not electrons are in a beam of light, how can a beam of light have voltage?

Waves or particles? Forget the photon, think waves for now.

When a charge moves, the local electric field is changed, and that change in the electric field moves away at the speed of light.

When a charge moves, that is a flow of current, and that changes the local magnetic field, a change which also propagates away at the speed of light.

So, the movement of a single electron causes a change in both the electric and the magnetic field to propagate away together, at the speed of light.

That is what light is, a disturbance of two fields. Since the electric field is changing, you can specify the change in the electric field as a voltage.

Do not mix the waves with the particles. Each has its place.

Once you can accept that wave explanation, you can ignore it, and then look at light from the particle, the photon viewpoint.

 

[berkeman]

Do electrons travel on those electromagnetic fields?

Not so much "travel on", more like "are influenced by". For the electrons in the metal of an antenna, the EM wave that passes the antenna accelerates the electrons in the metal wires of the antenna in a sinusoidal pattern, according to the forces exerted by the E-field part of the EM wave. So if the EM wave passing the antenna has the E-field component oriented sideways (orthogonal, or at a right angle) compared to the direction of the antenna wire, then no force from the E-field wave influences the electrons' motion along the length of the wire. But if the E-field component of the EM wave is parallel to the wire, then it exerts maximum force on the electrons in the antenna wire, which generates an AC voltage in the antenna that is picked up at the receive port of the antenna and utilized by the radio receiver attached to the antenna.

https://en.wikipedia.org/wiki/Antenna_(radio)

 

[berkeman]

Another way that EM radiation is used to influence electrons is in the Free Electron Laser:

https://en.wikipedia.org/wiki/Free-electron_laser

It's a somewhat different way of applying the same effects from EM-->Antenna Electrons, just with no metal involved with the electrons, and with a different purpose...

 

[weirdoguy]

One thing, because I think that is your main issue - voltage is not a property of electrical current per se (e.g. flow of electrons in metals). It's a property of electric field. People who don't know much about physics know voltage from electric current context, so I get why you are surpised.

 

[PeroK]

I think that photons are subatomic particles that make light. How is my understanding of photons wrong?

It's not very helpful to think of light as made of photons. There are two theories of light. First, there is classical electromagnetism, where charged particles create the electromagnetic field. There are no photons in classical electromagnetism. They are simply not part of the theory.

A more modern theory of light is QED (quantum electrodynamics). You could read Feynman's Strange Theory of Light and Matter, if you want to understand this theory.

Even in QED, light is not made of photons instead, the number of photons is a property of the quantum EM field. Which itself is a complex, highly mathematical entity. In any case, it's a field that permeates all spacetime. It's not discrete photons here and there.

Instead, photons represent the interaction of the field with matter and charged particles.

If we have a quantum EM field with a large photon number then it can be, in many cases, approximated by the classical field, with its oscillating electric and magnetic fields.

 

[Ibix]

Your explanation went over my head to some degree. My interpretation of what you wrote is that you are saying "Yes, beams of light have voltage."

I'd prefer to say it includes an electric field, but "has voltage" will do, yes. Do note @weirdoguy's comment in #9, though. Although voltage in our every day life is usually associated with a flow of electrons (that's usually what we use it to do), it doesn't have to be. It can be there without any electrons to push around.

What if the source of the beam of light is the Sun? If the beam of light is sunlight, is the source of the beam of light still charged particles?

Yes. The sun is made of plasma - atoms pulled apart into free electrons and nuclei, all of which are charged. Light comes from their interactions (originally from fusion in the sun's core). Terrestrial light sources involve chemical reactions (fire, glowsticks, fireflies etc) which involve electron exchange between atoms, or giving electrons energy and letting them re-emit it as light (lamps, LEDs, lasers etc). Always charged particles.

I think that photons are subatomic particles that make light. How is my understanding of photons wrong?

That depends what you think a particle is. Most people read "particle" and think "little ball bearing flying through space". It's a decent enough model for things like electrons under some circumstances (although there are plenty of cases where that's wrong too), but badly wrong for photons. They don't even properly introduce photons in physics degrees until you get to optional fourth year modules or postgrad work because there's so much stuff you need to understand before you can really follow what they are.

 

[pinball1970]

TL;DR: How is it possible for a beam of light to contain voltage?

I am currently reading Max Tegmark's book Our Mathematical Universe. Some of you are probably familiar with this book.

On page 167, Tegmark wrote the following: "It's not only 'stuff' that's made of Lego-like building blocks. As we mentioned in Part I of this book, so is light, being composed of particles called photons, inferred by Einstein in 1905.

Four decades earlier, James Clerk Maxwell had discovered that light is an electromagnetic wave, a type of electrical disturbance. If you could carefully measure the voltage between two points in a beam of light, you'd find that it oscillates over time; the frequency f of this oscillation (how many times per second it oscillates) determines the color of the light, and the strength of oscillation ( the maximum number of volts you measure) determines the intensity of the light."

It's my understanding that a beam of light is an electromagnetic wave of photons (and only photons) with no electrons. All my life I have always thought that electricity comes from a flow of electrons (and only electrons) with no photons. So I have always thought that a beam of light would have zero voltage because I thought that there is no electricity in a beam of light. Now I am aware of the fact that the letters "electro" in electromagnetic wave sounds like an abbreviation of the word electricity. But I have still always thought that there is no electricity in a beam of light because a beam of light is a wave of photons, not electrons.

Do beams of light have voltage? If so, assuming that only photons and not electrons are in a beam of light, how can a beam of light have voltage?

P.S. I am just a trucker. I am not a physicist or an engineer like many of you people. So please be gentle and don't chastise me for not knowing something that might seem very elementary to you.

Based on this paper. https://arxiv.org/abs/0704.0646

There are presentations on line regarding the paper and book.

I watched the presentation and the thing that struck me, was that 95% of the talk was the type of information you get from a physicist to a general audience.
Things are pretty certain of, observations, some cool images of distant galaxies and areas of uncertainty. So black holes, dark matter, dark energy, Hubble tension, GR, QM and associated mathematics (not too much) all good stuff.
The other 5% seemed like a wishy washy bolt on about the MUP. Perhaps I could watch it all again, time stamp it and post. Watch it so you don't have to. :)

 

[tech99]

If I place an electric circuit, containing a suitable indicator, in the path of an EM wave I can notice a current being created.

 

[sbrothy]

Based on this paper. https://arxiv.org/abs/0704.0646

There are presentations on line regarding the paper and book.

I watched the presentation and the thing that struck me, was that 95% of the talk was the type of information you get from a physicist to a general audience.
Things are pretty certain of, observations, some cool images of distant galaxies and areas of uncertainty. So black holes, dark matter, dark energy, Hubble tension, GR, QM and associated mathematics (not too much) all good stuff.
The other 5% seemed like a wishy washy bolt on about the MUP. Perhaps I could watch it all again, time stamp it and post. Watch it so you don't have to. :)

Are you voluntaring to act as his AI?

EDIT: Come to think about it, I'd trust you more!

 

[PAllen]

One other example is simply that if you charge metal ball or plate with static electricity, then you measure a potential difference (equivalent to voltage) between different points of the space near it, even though there are no electrons existing or flowing at or between those points. This gets at the difference between field source (charge on metal) and field itself, which can span vacuum.

 

[tech99]

One other example is simply that if you charge metal ball or plate with static electricity, then you measure a potential difference (equivalent to voltage) between different points of the space near it, even though there are no electrons existing or flowing at or between those points. This gets at the difference between field source (charge on metal) and field itself, which can span vacuum.

How are you going to measure potential difference without introducing electrons into the process?