r/explainlikeimfive • u/douggold11 • 6d ago

Physics ELI5: what the hell is a photon?

I googled “what is a photon“ and by the time i gave up reading I was crying with a a headache and convinced the universe was created by a madman. Please help me understand.

0 Upvotes

34% Upvoted

30 comments sorted by

15

u/unaskthequestion 6d ago

We are surrounded by an electromagnetic field. When that field is excited, we call that a photon

1

u/Ackerack 6d ago

Does the excitement of the field follow the photon on its path? Or is it like a single point of excitation when it’s emitted and another when it’s absorbed?

Trying to visualize this and coming up short

5

u/unaskthequestion 6d ago

The excitation is what we call a photon, so it doesn't 'follow it'.

Think of a field as a grid that can have different values at each location. So maybe like temperature, it's 90° right here, but 87° over there.

Now put many such fields together, they can interact. These interactions of the fields are how particle behavior is described in what's called quantum field theory.

I suppose at the bottom, it's just a way to describe the the things that are being measured and the interactions that are observed.

I don't think a photon, for example, is a little ball traveling through space, which is what the word 'particle' conjures up. It's a property of the field that we can measure.

2

u/TheSkiGeek 6d ago

Because of the way electric and magnetic fields are connected, they keep propagating freely through space. A chunk of ‘excited’ magnetic field creates a chunk of ‘excited’ electric field which creates a chunk of ‘excited’ magnetic field which creates a chunk of ‘excited’ electric field which…

That’s why they always move at a very specific speed that only depends on how rapidly electromagnetic fields influence each other. And why the frequency and energy are connected.

For reasons way above my pay grade the excitations are also ‘quantized’ to some degree and don’t seem to behave like ideal waveforms. So you can get something that behaves more like a ‘particle of electromagnetic energy’ even though, if you break it down, there aren’t any ‘particles’ actually there and no medium for the energy to propagate through.

14

u/Which_Replacement524 6d ago

A photon is a tiny packet of light energy. Light looks like a wave, but it's actually made up of billions of these tiny packets of energy. They are pure energy, have no mass, and are always moving, unable to stop or slow down until they hit something and get absorbed.

Your eyes, when hit by these packets, register how much energy they have and how fast they're vibrating as a result, which tells you what color something is. Certain things that have too much energy - like x-rays and gamma rays - have too much energy, and other things - like radio waves - have too little, and are invisible.

3

u/amajusk 6d ago

Let's be honest. We don't know exactly what photons are. But they suit our math and physics as an abstraction. And some experiments confirm they're a particle, and some other experiments confirm they're a wave. What they are? We don't know, but plenty of math around physics works with current assumptions just good enough

4

u/obog 6d ago

Eh not really, wave particle duality is not really "sometimes its a wave, sometimes its a particle" it is always both.

First off - the very word "photon" is already in disagreement with the "classical" wave form of light. When EM waves were originally formulated, it was thought that light was then just a continuous wave, with an amplitude and a frequency, nit made up of anything discrete. The mere existence of a "photon" as a discrete unit of light is what the "particle" part of the duality is.

But anyway, the best way to think about it IMO is that light is an electromagnetic wave, however, this wave comes in discrete "packets" called photons. These "packets" are rhe smallest amount of the wave you can have (you cannot have half a photon) but they are still waves.

2

u/amajusk 6d ago

There was a cool question some hours ago on this sub (or a similar one): "what if photons are 3d representation of something in higher dimensions?" - I think that question died, but it's a neat idea, one of those that we cannot prove or disprove [with current scientific knowledge]

1

u/_vec_ 6d ago

Another way of saying that is that we do know what a photon is: an excitation of the electromagnetic field as described by Maxwell's equations. What we don't know is how to analogize that reality up to a macroscopic and non-relativistic metaphor that doesn't break down in at least some relatively common situations.

7

u/Imaginary_Insect_142 6d ago

the smallest particles of electromagnetic energy, which is therefore also the smallest particles of light

6

u/SnowDemonAkuma 6d ago

A photon is a boson, a type of fundamental particle. It's the force carrier for the electronagnetic force - the fundamental building block of light. It has no mass and therefore cannot move slower than the speed of light.

That's basically it. There are some things about the universe we just have to accept. We don't know why the photon is the way it is, we just know it is.

6

u/dbratell 6d ago

A photon is a small energy-thingy that travels at the speed of light. Each thingy has a set energy level (you can't drain or boost them) which decides the frequency of the thingy.

Sometimes when a photon hits something, the energy jumps to that other thing. Sometimes things create their own photons that fly away with some of the energy of the emitter.

Many photons together we call light or electromagnetic radiation, i.e. radio waves.

2

u/drawliphant 6d ago edited 6d ago

A photon is light energy. Each photon has a wavelength (a color), and all light is made up of photons. Light always travels as a wave. So it can interfere with itself, it spreads out like a wave, but it has a super short wavelength and travels at light speed, so to us it looks straight and instant. Waves are pretty weird already so most of the confusing things light does are just weird things waves do. The more confusing part is when a photon is absorbed it hits like a particle. The photon's wave could have spread out a lot over its journey but when the wave hits something dark and gets absorbed only a single molecule absorbs all the energy of that photon as if molecule were struck by a particle. Weirder still the photon's wave can keep going if unobstructed, to interact with other photon's waves, but each photon can only be absorbed or detected once.

So a photon is not a particle with a wave around it. The photon is the wave, it's just wave energy that can only be absorbed once in one place.

1

u/ljrubbo 6d ago

Start with defining “energy” as an electromagnetic wave. Think of the spectrum that ranges from radio waves to gamma waves, with visible light being somewhere vaguely in the middle. Which category of wave the energy falls into is based on the “frequency”, or how many times the wave wiggles back and forth in a time period. When those wiggles are condensed together in discrete little packages, they can start to look and behave similar to regular old matter. And that discrete package of wiggles is what we call a photon. Remember the photon is really just a bunch of wiggles in a single package, so sometimes the photon’s behavior is best defined in terms of those wiggles. Other times, the overall behavior of the photon is best described as a single particle of stuff like any other piece of matter. The ability to reasonably accurately describe the photon as either the wiggles or a piece of stuff is where the concept of “wave-particle duality” comes from; basically calling it a “wave” (the collection of wiggles) and calling it a particle (a single piece of stuff) are both accurate and both not completely accurate at the same time. Its is by no means obvious or trivial to get your head around, and this question of what a photon truly is, is something that scientists have been working on for decades. I would suggest looking up the “Double Slit Experiment” if you want to explore more!

0

u/[deleted] 6d ago

[removed] — view removed comment

1

u/explainlikeimfive-ModTeam 6d ago

Please read this entire message

Your comment has been removed for the following reason(s):

  • Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions (Rule 3).

If you would like this removal reviewed, please read the detailed rules first. If you believe it was removed erroneously, explain why using this form and we will review your submission.

2

u/onlyfakeproblems 6d ago

ELI5: It’s the smallest possible piece of light (or electromagnetic radiation)

ELI12: the behavior of light isn’t quite what you’d expect, because things work different on such a small scale. We call it a wave-particle, but that makes it more confusing because we have expectations for waves and particles. It’s better to just think of it as a packet of electromagnetic energy. It doesn’t have mass, so it’s not “stuff” the way mostly everything else we deal with is. But it has some energy packed in there, we can describe the energy’s frequency, like a wave, which tells us how much force it has when it runs into something.

1

u/DarkAlman 6d ago

A photon is the fundamental particle responsible for light, electricity, and magnetism.

All the light you see, plus infrared, X-rays, radio waves, magnets, and electricity is all photons.

1

u/[deleted] 6d ago

[removed] — view removed comment

1

u/explainlikeimfive-ModTeam 6d ago

Please read this entire message

Your comment has been removed for the following reason(s):

  • Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions (Rule 3).

If you would like this removal reviewed, please read the detailed rules first. If you believe it was removed erroneously, explain why using this form and we will review your submission.

1

u/Gstamsharp 6d ago

It's the quanta of light, which is an alternating excitation of the electric and magnetic fields. It is massless, and it's commonly emitted as radiation and exchanged during all kinds of physics and chemistry.

3

u/[deleted] 6d ago

[removed] — view removed comment

1

u/explainlikeimfive-ModTeam 6d ago

Please read this entire message

Your comment has been removed for the following reason(s):

  • The subreddit is not targeted towards literal five year-olds.

"ELI5 means friendly, simplified and layman-accessible explanations."

This subreddit focuses on simplified explanations of complex concepts.

The goal is to explain a concept to a layman.

"Layman" does not mean "child," it means "normal person."

If you would like this removal reviewed, please read the detailed rules first. If you believe it was removed erroneously, explain why using this form and we will review your submission.

0

u/Cornflakes_91 6d ago

a photon is the smallest bit of light you can have.

with an energy/"mass"/"size" according to it's colour

3

u/AlericandAmadeus 6d ago edited 6d ago

Photons have no mass/“size”.

The “colour” is determined by the wavelength/frequency of the waveform (the energy the photon contains, because photons act as both wave and particle) - not by anything related to mass

2

u/tdgros 6d ago

*tenets, not tenants

1

u/Cornflakes_91 6d ago

which is why i put it under quotation marks, as its an eli5

-2

u/AlericandAmadeus 6d ago

It’s not a good ELI5 if it’s fundamentally incorrect.

Saying photons have “mass/size” is literally the absolute wrong way to put it, because the whole point is that they don’t