#photons #massless #quantumphysics
Hey there! Have you ever wondered why photons, those tiny particles of light, don’t have mass? 🤔 Let’s dive into the fascinating world of quantum physics and find out the answer to this intriguing question!
### The Nature of Photons
– Photons are elementary particles that make up electromagnetic radiation, including light.
– They are known for their dual nature, behaving as both particles and waves.
#### Mass vs Massless
So, why don’t photons have mass like other particles do? Here’s the scoop:
1. Photons are gauge bosons, which are force carriers responsible for electromagnetic interactions.
2. As force carriers, photons do not experience the Higgs field, which is responsible for giving mass to other particles.
### Explanation in Layman’s Terms
Imagine you’re at a busy airport 🛫. Passengers with heavy luggage (particles with mass) move slowly through security, while those without luggage (massless photons) zip through quickly.
In a similar way, photons move at the speed of light because they are massless, unencumbered by the baggage of mass.
### Real-Life Examples
– Solar panels harness the energy of photons from the sun to generate electricity.
– Photosynthesis in plants relies on the absorption of photons to create glucose.
### In Conclusion
While it may seem counterintuitive that something as powerful as light could be massless, the unique nature of photons allows them to travel at incredible speeds and play a vital role in the universe’s workings.
Next time you flick on a light switch đź’ˇ, remember the massless wonder of photons illuminating your world!
So there you have it! The mystery of why photons don’t have mass revealed in a way that’s easy to understand. Keep exploring the wonders of the universe, one photon at a time! ✨
Think of a photon as a [burst of energy](https://www.advancedsciencenews.com/wp-content/uploads/2022/10/single-photon-source-for-quantum-encryption.jpg) that’s tiny enough to be thought of as a dot (particle) also. It doesn’t have rest mass because its energy is in its frequency.
If the photon had mass, it cannot travel at the speed of light as it would require infinite energy according to the equations of relativity.
Since photons travel at the speed of light, they have to have no mass and all their energy comes from their momentum.
This feels incorrect to anyone only familiar with classical physics because classically momentum is mass times velocity (speed with a direction). But with relativity, you have to consider momentum as a fundamental concept independent of mass.
Why would they have mass?
Theories where all particles are massless are much easier. So historically the question was the opposite: How can particles have mass? That question was especially tricky for particles that are responsible for interactions. In the 1960s, a couple of theorists found a way to give some of these particles mass: The Higgs mechanism. They predicted that there should be a new particle, too, the Higgs boson. If it exists (it was discovered in 2012) then the Higgs mechanism exists which allows the W and Z bosons to have mass, but you still cannot give a mass to all particles. The photon has to stay massless.
Some particles (quarks and leptons) have mass because they interact with the Higgs field, they make up all physical things. Some particles (bosons) have no mass because they don’t interact with the Higgs field. They are called “force carriers” because they exert forces on matter particles. Photons (which are bosons) exert forces on electrons (which are leptons.)
The deep reason for why and how photons have no mass is something that Physicists have been trying to figure out since Einstein. Truely understanding photons would revolutionize modern science. What we do know is; to make all the physics equations that we have work right, we have to assume photons have zero mass.
For an interesting read about what happens when things with mass get close to the speed of light I suggest : [Relativistic Baseball (xkcd.com)](https://what-if.xkcd.com/1/)
Someone explain then if E = mc^2 then if m is 0 so is E so massless particles can’t have energy, but light has energy???
They just don’t. We are describing a fundamental property of a particle. There’s no why; it just is massless. It’s not a consequence of anything.
Photons “don’t have mass” because that’s how our math and understanding of science and light speed particles was written and is understood.
However as with any science, this could be proven wrong in the future, and in reality photons do “have mass” in that they are an actual physical thing in our universe but they are just so blasted small and move so stinking fast that we (to our understanding) can’t “weigh” a single photon to figure out how little something has to weigh/how little of mass is required to be able to travel and light speed.
In classical mechanics, mass is the relation between a force and the acceleration it creates. If I push you and you back off 2 steps, then your mass is whatever value makes this relation true.
In relativity mass changes a bit, because you consider that mass is not just some number, but it is a form of energy. The famous equation from Einstein shows that: E=mc^(2) just means that the mass m is stored energy that depends on the speed (if you remember classical mechanics, think a bit of the potential energy of gravity, where the energy is “saved” in the body when it is in height and it is “freed” when it falls). Obviously this equation in reality is much more complex because energy doesn’t only come from mass but from movement as well (like the classical kinetic energy).
If you have that the amount of energy is fixed, then the only things you can change in the equation are the speed and the mass. Basically we say that light has no mass because it is the only way to balance the equation that will manage to give you that the speed is actually the speed of light.
You have to take this explanations with a grain of salt, since they are wrong for the sake of clarity. No matter how simple you make it, it will never be ELI5. Others here have explained the real stuff, but it is way out of the scope of the sub. For fuck’s sake, when would you ever tell a 5yo about the Higgs field.
Think about a wave of water. The water has mass. The wave doesn’t.
Light isn’t stuff. Its a wave travelling through the stuff.
I’ve heard that light moves slower in different mediums. I also heard about an experiment that managed to “freeze” light.
If I slow down a photon so it’s not moving, then release it into a vacuum, where did its energy to get to light speed come from?
Same with electrons, why can they just keep moving?
How would a solar sail work if it has no mass?
I can only surmise it has no mass because it doesn’t interact with the Higgs field. Why that’s the case is beyond me.
Why would it? A lot of standard model particles don’t have mass. It’s not that special.
A bit of a more nuanced answer:
Actually we don’t know if photons are truly massless. We know they are practically massless, we’ve done experiments which let us know that their mass is smaller than a very incredibly tiny amount. However, we don’t have any experiment confirming that a photon has absolutely no mass, because we haven’t found a way of measuring that.
That’s actually a really interesting topic.
E=mc^2 tells us (among many, many things) that they do because mass and energy are actually the same thing just in different forms. You can do the math yourself and calculate the mass of a photon from any part of the EM spectrum. That fact is essentially how solar sails work, that infinitesimal amount of energy/mass they embody is imparted onto the sail, giving it forward momentum.
Higgs posited the theory that mass is actually a fundamental force all on its own, not unlike the EM force, and it’s the interaction between, what was later dubbed, the Higgs field and everything else that results in what we describe as mass onto particles. This was, basically, his attempt to reconcile General Relativity with quantum mechanics by showing that gravity is not a fundamental force, but rather an effect that mass has on space time.
Today, we know the Higgs field exists so he was bang on the money. The issue now is how to reconcile it with E=mc^2. How do things that don’t interact with the Higgs field exist at all if mass and energy are the same thing?
We know Einstein was right, and we know Higgs is right, we just don’t know how the two jive together.
Photons are not physical particles. They do not exist from a physical point of view. It is an abstraction that scientists established to quantify the properties and energy of light.
Said in simpler terms photons are not small balls of light flying around.
All of the photon’s mass is in its momentum. Photons have zero ‘rest mass’ because from the moment of creation to its destruction, it’s always moving, it never “rests”. When people talk about mass in the conventional sense, what they’re really talking about is ‘rest mass’.
They’re not ‘massless’ per se, they just have no ‘rest mass’ – which is what everybody is talking about when they use the word ‘mass’.
Photons do have mass but is negatively charged and gravity is mostly negative charged thus only those with positive charged particles appear to have mass.
Photons have momentum because they have mass.
So electrons can be accelerated by the synchrotron till light speed because they are negatively charged thus not slowed down by gravity, as opposed to protons that still had not been accelerated to light speed before.
This question has always bothered me. If the photon is massless, then how does it interact with gravity to create gravitational lensing? How does it move at different velocities through materials, and thus diffract? How could Cherenkov radiation be produced when an object passes through a material faster than the speed of light in that material? How could we detect from a black hole merger the X-rays before the radio waves?
IMHO, the photon has a negligible mass that we simply haven’t been able to detect yet through experimentation.
There are no truly fundamental answers to this question. We know that photons don’t have mass, but we don’t have any idea why.
For example, some might be tempted to point out that the photon travels at the speed of light, in order to do so it cannot have any mass.
That statement is true, but it does not explain *why* the photon has no mass. It only leads to circular questions and answers like, “Why do photons travel at the speed of light?” The answer is that they travel at the speed of light because they have no mass.
And so we are back where we started.
The reality is that physics doesn’t concern itself with the “why”, only the how. Physics pursues ever more accurate means to explain how our universe works. Along the way, this results in a deeper understanding of why particles behave the way that they do, but as you traverse down the scale to sub-atomic particles, we begin to reach the endpoint of what reductive insights can deliver.
Richard Feynman is one of the greatest theoretical physicists of all time. He is the person responsible for the diagrams that we use to depict the interaction of sub-atomic particles. Many years ago he was asked why magnets repel each other, and his response is a fantastic dive into the difference between why and how. I have linked to a video of the answer below. If you enjoy these kinds of questions, you’ll enjoy this answer.
[https://www.youtube.com/watch?v=MO0r930Sn_8](https://www.youtube.com/watch?v=MO0r930Sn_8)
But if photons don’t have mass they would be able to escape a black hole and should not be affected by gravity but gravitational lensing and black hole studies prove otherwise.
They don’t interact with the Higgs field. Why don’t they interact with the Higgs field? They just don’t, as far as we know, things aren’t they way they are to achieve a certain objective.
The simplest explanation is that photons do not have a rest energy as they cannot exist in a rested state which is why their mass is 0.
Photons do have momentum and can and do transfer kinetic energy to anything they “hit”.
The reason why they have momentum but not mass is because of their wave / particle duality.
The way they transfer energy to an object is more analogous to a boat floating on the water and the waves moving through the water transfer some of their energy to it.
This means that the energy is taken from the waving motion rather than from any given particle or massive object which hits another like say a ball hitting another ball.
As for the deeper question of why there isn’t an answer and never will be none of the fundamental properties of the universe have to be the value they are but if they weren’t we would be living in a very different universe and possibly not even living at all.
You need to learn some terms used in special relativity that are different than what most people are used to. When physicists say things with mass can never travel at c (speed of light). , we mean things with rest mass (see my post above going into more detail). When scientists use shorthand and say particles without mass always travel at c this needs to be more precisely stated. Particles with no rest mass (like photons) always travel at c. However in special relativity photons have relativistic mass, but no rest mass. This is what is meant. So photons have relativistic mass and travel at c because they have no rest mass (note I am using some outdated terms here but I think it is a bit easier to understand. using them for ELI5). Anything with rest mass cannot travel at c, any particle without rest mass always travel at c, those particles traveling at c however do have relativistic mass. These definitions are key when talking about special relativity.