Why No One Knows If Photons Really Are Massless: What if they Aren't?
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- Опубликовано: 17 май 2024
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REFERENCES
How Faster than Light Breaks Causality: • How Faster than Light ...
Why isn't the speed of light infinite: • Why isn't the speed of...
Why is the Speed of Light what it is? • Why is the speed of li...
Secrets of neutrinos: • Neutrinos: Why Do Thes...
How gluons work: • Why Don't Protons Fly ...
Paper on theoretical photon mass limit: tinyurl.com/22bgk6ns
Measured speed of photon: tinyurl.com/2y896abt
Guaranteed answers to your questions on Patreon: / arvinash
CHAPTERS
0:00 Do photons have mass?
1:34 Why we presume speed of light is the maximum speed
3:13 If light is not the maximum speed, then what is?
4:51 Why don't we know whether photons are massless?
6:58 Wouldn't the universe collapse if photons had mass?
8:10 What would we see if photons had a significant mass?
10:04 So do photons have mass or not?
11:13 How to learn advanced math to learn physics in depth
SUMMARY
“Do photons have mass?” in most textbooks, the answer is no. But is it proven that light does not have any mass? Has anyone every actually confirmed this in a measurement? No.
Einstein’s theory of relativity tells us that massless objects always move at the same velocity in a vacuum, which is the speed of light or 299,792,458 m/s. This assumes that the photon is massless. But it doesn’t have to be. We presume that the photon is massless because we have not measured anything faster.
If a photon has a slight mass, its velocity is not the maximum. Bit since we have not measured anything faster, we presume that the speed of light is the maximum velocity possible.
Conceptually, it doesn’t matter what the speed of light is in special relativity. What matters is the speed of information flow. This is necessary to ensure that causality is not violated. In the case where the speed of light is less than c, then c would represent the speed of information flow, not the speed of light. This speed would be the maximum speed allowed in the universe. So the true limit of special relativity is the speed limit of information flow, not the speed of light.
This would not be a problem in science because since photons are the fastest way we know to send information, it would just mean that we don’t have a way to communicate at the maximum speed, but only at the speed of light, which would be slower than that maximum.
This would not invalidate Relativity theory either. It's just for practical purposes we state relativity in terms of speed of light, but we could have just as well say speed of causality to be more specific.
The problem is that we actually don’t know if photons really are massless because we have not been able to devise an experiment to truly test this. Experiments tell us that its mass can’t be larger than 10^-18 eV, because we would have been able to detect that mass.
Our theories tells us that it should be massless, but there is nothing else we can measure which could be faster.
There is only one other known particle that is thought to be massless, the gluon, but due to the laws of the strong force, these gluons are not free and are always bound with quarks. So we can’t measure their speed.
The lightest particles we know of neutrinos, would still be around one quintillion times heavier than photons.
If photons have a very slight mass, the universe would not look much different but if it had a significant mass, then we would see some differences. One example would be that the electromagnetic force would become finite.
Another change you would notice with a significantly massive photon is that higher energy photons, that is photons with a shorter wavelength, would travel faster than longer wavelength photons. This probably would not make much of a difference if you were looking at still objects, but a moving object like a fast white car at a distance might look like a blur of colors, with the blues being further away than the red. This is because the blue color within the white of the car would reach your eyes before the red color. Another effect that would come with a massive photon is gravity bending light like a prism.
#photonmass
#photon
The observable universe would appear to be much smaller because light from very far distances would not have reached us yet. The cosmic microwave background, or CMB, might not be visible because its light may not have reached us yet.
Since we don’t have any observations that support a truly massless photon, the possibility that it really does have some mass, at this time, cannot be excluded. 
Наука
Fun Fact: Lamps in video games emit photons and consume electricity just like in real life.
🤯
....as does the entire screen you're using to view said video game.. 🤔🤨😂
😅😂🤣
Thanks
But the dark that represents "no light" in video games also consumes electricity. The only difference between that and anything we can see or measure in real life is that in order to have darkness, we must deflect light.
"I don't know" - For the countless physicists and armchair physicists that will give an answer, then passionately defend that answer, those three words are profound. Thank you Arvin.
You sound pretty sure of yourself. Is “I don’t know” a good answer? For my part, I’ll just say I don’t know if it is or not.
;)
,,, nuff said ... eye second th' notion ...
I'm confused by what I take to be the narrative that physicists are generally unwilling to admit that we don't have definitive answers for things...
I really liked how professor John Christy from The IPOCC stated it, he said “Scientist should always begin an explanation with the words - here’s what we think we know as of today!
You have been lied to and enslaved 👉 The Connections (2021) [short documentary] 💖
Finally something that is worth watching on youtube, that a 6 yr old or a 60 year old can learn something worthwhile.
Thanks Arvin for this highly thought provoking video!
There's a hypothetical phenomenon called the Scharnhorst effect, where a tiny gap in which vacuum fluctuations are suppressed (like with the Casimir effect), light should be moving a little faster than C. The idea being that photons are slowed by interaction with vacuum fluctuations, so if there are fewer vacuum fluctuations then you get faster photons. It's a tiny effect, too small to be detectable with current technology (like 1x10-36), but it suggests that even if photons are massless that they travel a tiny bit less than the maximum speed for the universe.
Could this tiny difference be related to the apparent redshift of light coming from distant galaxies?
Exactly even a tiny amount of mass is something
@@JohnnyWednesday I haven't heard of this affecting the frequency of light. I'm hardly an expert, though.
@@JohnnyWednesday that would be a HUGE difference, finding that the universe is not expanding after all. Which kinda sounds more plausible, than imagining that the sapce between the subatomic particles is constantly expending...
Imagine how that would change the calculation of galaxies ages and understanding better the grate attractor....
@@JohnnyWednesday Probably not. Redshifting requires that the photons change their frequency as they travel through space. While a massive photon would not have the same frequency as its massless counterpart, it would keep its frequency.
Also, the redshifting being an effect of photons being massive would leave other periods unaffected (such as how long half-lives to be reached), but we see the effect of redshift on them too.
Interesting video! Just a minor point: at 10:20 you say that the CMB might not be visible because its light may not have reached us yet. This doesn't seem correct to me because the CMB started everywhere in the universe, including here. It's just that we would receive now CMB light which started closer to us and the CMB would still be visible, as it is everywhere in the universe.
The CMB would still appear differently than it currently does though.
Yeah this is right, there might be a million other reasons we wouldn't see the CMB if photons had mass, but not because it hadn't reached us yet. The CMB permeates all parts of the universe at all times
The cmb could very well be the physics equivalent of hawking radiation in which case the universe could be infinitely bigger, but we could never see beyond a specific light cone that effectively represents an event horizon for us.
@@danielkirk4755 I was under the assumption that the CMB came from the past from what people call the "Big Bang". People assume it started everywhere, all at once, but I don't remember any proof of this theory nor proof of the opposite that it started at one point. Contrary to what you might hear though, I've heard the readings are not perfectly symmetric and so suggesting it comes more from one direction which might suggest either a point of origin or a bias in how it travels.
If you're however talking about more recent expansion and not early inflation/big bang, then I'd still question your assumption since we cannot even experimentally agree upon rates of expansion of the universe.
In summary, I'd ask: are you *sure* the CMB 'permeates all parts of the universe at all times'? If so, how and why? Why does it not appear even? Why can we not experimentally agree upon universal expansion rates? Do these two phenomena even relate at all? Are you sure we would still see photons from the CMB (or photons in general) if they were massive enough? I suspect if they were very massive, they would be caught by their galaxies, massive enough by their solar systems. But, then I don't know how such a universe would even operate at that point.
@@TletnaNearer anyway.
2:18 “If there’s no mass, that is, if M is zero” … This wording should actually be “if there’s no REST mass, that is, if rest-M is zero” … bcus rest mass is what you’ve implied in this equation. For it is the rest mass plus the momentum energy which equals the total energy. So, the question is wether photons have “rest mass.” We’re not wondering about relativistic mass. BUT, we know that a photon has no rest mass bcus a photon can never be at rest, since there is no frame of reference from which to view the photon at rest. Therefore the rest mass of a photon is definitely zero. It shouldn’t matter that light is just the fastest particle we know of and there could be faster speeds possible. It is only that the light travels with invariable speeds from the perspective of any observer which inherently causes light to be the fastest speed possible, period. If the rest mass equals zero, it means all of the energy in the photon must be “momentum energy.” There can be no rest mass. If there could be rest mass for a photon, then the speed of light would not be invariant, for that is the essence of the special theory just there- the fact that light traverses across space invariably from the perspective of all observers. The Michelson Morley experiment proves that light is 100% invariable against any motion of any observer, so we can deduce here from Einstein’s answer to the Michelson Morley experiment that light must be 100% rest-massless. Light does not stand at rest from any perspective, ever. This is why Einstein said the photon is massless. It wasn’t just an assumption he made. Rather, it was the only possibility.
I thought that one of the reasons we discovered Neutrinos have mass is because we have observed them changing flavors. Since they "experience" time, they do not travel at c, hence they cannot be massless.
Light is massless as it travels at the highest speed. Although they have momentum
@@tonyrock5313 The whole premise of the video was to suppose what if light had mass...
You have been lied to and enslaved 👉 The Connections (2021) [short documentary] 💖
@@tonyrock5313 If it doesn't have mass, how can it have energy? Aren't mass and energy pretty much the same thing in different "states"?
could you also check for mass by slowing the particle down? like if light did have mass, you should be able to slow it down until it reaches a standstill?
Also if photons were massive then the QED interactive Lagrangian wouldn't be symmetric (e.g. under Lorentz transformations or gauge transformations) and conservation of electric charge would be violated. A photon field as a gauge field (with 2 DoFs only instead of 3) is necessary to conserve charge.
Other terms would need to be added to the equation to balance out. I didn't get into this, but you make a very good point that I may want to cover in a more in depth video. There are of course other equations that would also need to change.
@@ArvinAsh Would that also change whether black holes could exhibit charge? If the range of the EM force became finite, would the field lines essentially have "ends" like other finite range forces, and get swallowed up behind the event horizon?
This supposition that photons are entirely massless has always bothered me. So why do they get trapped in black holes? Great video Arvin!
because black holes bend space-time? duh?
where do you think photons (whether waves or particles!) travel *on?*
if you can't grasp how the bending of the 3-dimensional space affects the phenomenon you call light, whatever ITS true nature, then you have to go back to square 1.
Because the escape velocity of the black hole is faster than the speed of light.
E=mc^2. Photons aren't different from anything that has mass even if they are massless because they are energy.
Sorry for responding but I want to better understand your question. Would you be more specific in your question? Photons are bits of energy. Energy is equal to mass per Einstein's general relativity theory. Energy and mass travel in a "straight" path unless there is a force changing its path. Gravitational force in a black holes attracts light only if light or photons or any electromagnetic radiation reaching the event horizon of a black hole. At this distance to the center of the black hole, everything will be trapped by the black hole including information. Light as well as mass in vacuum travel through the shortest distance or less action or geodesics in space time. The curvature of space time in a black hole is so high that everything trapped by a black hole is destined to never have a chance to escape the event horizon.
Lights travels in space-time.
Mass bends space-time.
Black holes have so much mass that they bend space-time to a point where all possible paths (beyond the event-horizon) go inward. Anything traveling that path stays inside, and doesn't come out.
Ergo: a photon (light) travelling on a path which intersects the event-horizon of a black hole, can not escape anymore and stays inside forever.
Another commenter asked how it is possible that light is massless, yet it seems to be influenced by gravity (eg: Einstein rings, black holes, etc etc), which would mean that photons should have mass afterall.... But that is in fact false. Light is NOT influence by gravity at all!!! Yes, many say gravity influences light, and many examples might suggest so, but that is in fact just a big 'dumbing down' to make other things easier to explain.
Light is only influenced by curvature of space-time. It simply travels in strait paths on the fabric of space-time. However, what is happening is that gravity influences space-time, it curves it; The bigger the mass/gravity, the more curvature space-time will get. And as a result, if space-time gets curved, light follows that curved path. That is all (again, dumbing down A LOT here).
TL/DR;
Light always travels in strait lines upon the fabric of space-time.
Gravity/mass influences space-time (by bending/curving it).
The 'shape' of the fabric of space-time dictates the path of light travel, NOT gravity/mass itself.
Analogy:
A train always travels in a strait line. It does not have a steering wheel.
But mountains, valleys, etc, influence where tracks go.
If a track suddenly goes into a mountain wall, the train will not suddenly steer left or right to avoid that wall!!
It simply continues to follow the track (and smashing into the wall).
It is not the geography itself that dictates where the train goes, it is the tracks that tell the train where to go.
The train always simply travels strait following the tracks.
(and if the tracks go in an enough deep and steep valley, the train wont be able to climb out of it on the other side, and will stay in the valley forever
Thank you, thank you, thank you so much for including your work with the math equations. You did it so seamlessly and it was beautiful.
Fundamentally, I do not think travelling faster than light breaks "causality", because once something is done/happened, you cannot do anything to undo it. As an example, we can now travel faster than sound. If thunder were to happen, theoretically, we can travel to a location where the sound of thunder has not reached it yet, and inform the people there that lighting has occurred some distance away. There is nothing the people can do, to undo the thunder, even though they had advanced warning of it.
gravitational waves also propagate at the speed of causality, so we could compare the time it takes for the light from a neutron star merger to reach us , compared with the time it takes to detect it using LIGO :)
Won't work
@@lazyobject5797thanks, Professor. 🙄
It could work if you compare the time delay between the arrival of gravitational waves from neutron star mergers and the subsequent detection of the light from the accompanying supernova. I think they actually did something like that but I'm on a train and can't do the research.
@@levako05d but given that the mass is so low, probably that wouldn't be enough to detect the difference.
Isn't that only if gravitational waves really travel at the speed of causality?
Its the same issue like with the EM field, we suppose it also changes with that speed. We suppose, not we are certain.
This channel gets to the inconsistencies and gaps in our understanding every time
Great video Arvin👍😉
This is a profoundly arcane topic of which even an excellent video can barely scratch the surface. It has implications for nearly everything in modern physics and cosmology.
Nice and easy to understand explanation! 👍👍
I was waiting for you to quote a physicist as I’m quite certain from grad school that integer spin bosons (such as photons) are always massless (and this is necessary for all of quantum theory to work).
Some equations in their current form wouldn't work. They would need to be modified to account for a massive photon. And as far as I know, this is feasible in most cases, but yes, the math gets very complex.
What about the Higgs? Integer spin, not massless.
Arvin, I just love the way how you explain super complicated topics in an easy to understand way!
Just its bs....P=mxv.....so it would also be zero if m=0. Morons.
Great video again. I studied Ecology and in behavioural ecology and specifically "signalling theory," information is seen as the change that takes place in the receivers of signals. Signalling theory also states that for a signal to create change in the recipient it must be new. For example if I were to say to you E = mc² it wouldn't be information to you.
Excellent video great how you show the importance and relationship to causality in this we generally don’t think of these two together but has your video shows very important concept.
I'd think that gravitational wave experiments would be a great candidate for figuring this out. Since GWs don't have mass, we can observe ripples and correlate their time of arrival with a flash. Biggest challenge is probably to figure out whether the GW and photons were indeed emitted in the same instant (or close enough to be a significant indication). Would also have to be corrected for things like gravitational lensing, but AFAIK this is something we're already quite good at.
Unfortunately your radar detector detecting your gravitational waves would have to figure out which flash to associate which gravitational waves could have departed from the Flash that is finally arriving only at the speed of light, that would definitely be a pretty tall order!
Great video, as always! I'd suggest to make one about the cause and nature of inertia, because so far I haven't been able to find any good explanation online, so maybe it could be intresting for other people as well.
An object’s velocity doesn’t change unless there’s a force acting upon it. Inertia doesn’t *need* a cause since it is just the absence of anything funny happening.
inertia is a consequence of what happens at a lower scale. a low enough scale would be somewhere you could analyze the motion of a massive (that possesses mass) particle. current models give you predictions but don’t venture in offering an intuitive description. you may view inertia as derived from wave propagation. A wave has energy and momentum conservation, but the mechanics are different from a body sliding through space. points in space are “charged” resulting in a wave.
inertia? proper, true inertia? that's magnetism's twin, Michael Faraday's dielectric field, also known as America's best kept state secret ;)
it would be extremely accurate and logical to call all reported UFO's and flying saucers as "dielectric field craft" :P
@@maeton-gaming er, no
This is absolutely throwing me for a loop!! The wave equation follows from Maxwell's equations with unknown either B or E. One can determine from this the speed of the wave, 1/sqrt(u0*v0) which is approximately 3×10⁸ m/s.
Arvin very good topic
chosen for discussion.
I have drived the equations for calculating mass, force and gravity exerted by photon. These equations specially gravity of photons answers many of the challenges of the space, time and gravity.
What a dark life for light. It gets to be the fastest thing but it can't go slower. It helps us all see, but it never see's anything.
If photons were found to have some miniscule mass, would that mean they do get to experience time after all? Also what happens if it is the information they carry that provides the mass?
even if photons didn't have mass, they "experience" time from "our inertial frame" because they are effected by "gravity", which is the difference in the rate of passage of time. Photons must have a size to be able to be effected by time in this way... one side has less time than the other by a VERY VERY small amount (unless around objects like blackholes) because photons "bend their path by gravity" (see: gravitational lens), they are effected by time. However, from the photons perspective, it is emitted and absorbed/reflected at the same moment of time, with NO space in between (as it was lorenz collapsed by moving at c).
The implications of information having mass is that your thoughts (and emotions) have more weight than you think and were taught to believe. 😎
Say what you mean, follow through on your words, don't lie, and be nice. "they" are you. All is the one and the one is the all.
And what about Fermat's principle?
Would Snell's law still work?
@@govcorpwatchPhotons do not have a size. They are point-like particles. Gravity bends spacetime, which photons travel though at the speed of light. Thus they appear bent. They are not "pulled".
@@Sarafan92 Interesting. there are many videos on YT on the size of photons. they don't have a theoretical maximum limit on the volume/size of the wave function. photons, being a wave, directly contradicts the idea that they don't have a size. their typical size is one wavelength. One side of the wave experiences time differently in space-time than the other side, thus bending the light into slower time. They are not "pulled", it's like a space-time refraction. refraction is light bending when it the speed of light changes. light bends in a similar refraction around mass from the "changes in the speed of light from differences in the passage of time". It is space-time after all.
is the size of the wave function the size of the photon?
does modeling a photon as a point for Quantum Mechanics make a photon into a point?
relevant length is the Compton wavelength λ= h/E
@@Sarafan92 i am curious, if photons are point particles how exactly can ONE photon at a time go through two different slits and then self interact to create a diffraction pattern?
You did such a good job explaining it that I may have understood some of it.
Arvin you are the guiding light for all those who want know more about research in physics
The CMB would still be visible, just from a closer distance, and maybe we'd measure a higher CMB temperature as a result.
Good. Valid comment,.
Using the vacuum permittivity and vacuum permeability constants in Maxwell’s 4th equation, I thought you could derive the speed of light. If so, maybe it’s a question of measurement accuracy for different constants.
@@RockBrentwoodwhy would you put so much effort into a comment? You’re smart enough to type all that and sound knowledgeable but not smart enough to know that a text that long will be off putting and not worthwhile for almost anyone who interacts with it?
@@willrobbins2550don't generalise.
@MrM good question. Here's a simpler response. Vacuum permittivity and permeability are fundamental constants - we had to measure them to find out what they are! You could measure them, or, you could measure the speed of light directly. But in terms of the result, it shouldn't make any difference, assuming that is, that we can measure all of these things with the same degree of accuracy.
There is no theoretical derivation of any of these constants, they *have* to be measured. So what does this tell us? Well, unfortunately, not quite as much as we'd like. Knowing the speed of light, however accurately, does not actually tell us whether there is anything that travels faster, like 'information'. It's difficult to imagine what that might mean in practice - we always think in terms of a medium and a mechanism, and in the case of light, that's well understood. But information? That's tricky. The only thing I can think of is gravitational waves, which carry information, through the fabric of spacetime itself, rather than through any quantum field. Or at least that's the classical model; people researching a theory of 'quantum gravity' may see it differently. Gravitational waves are thought to travel at the speed of light, but, as Arvin points out, they may be able to travel faster, if there is such a thing as 'speed of information', as distinct from speed of light.
What we need is a lot of extremely accurate observational data, to see if we can measure anything that appears to be travelling faster then the accepted value for c.
@@kindlingking people like you are the worst
I know you’ll probably never see this, but just in case. Just some advice, when you point to the pop up link you need to tell people they can find the link at the end of the episode also. That way, if me or anyone else enjoying your show or episode doesn’t need to stop watching. Maybe you do put one up at the end, haven’t made it that far up. If that’s the case I guess my advice would be to just mention it in the moment so your viewers know and don’t have to choose between the link your pointing at mid show and the show itself. Love what your doing keep it up!
Fantastic and a sincere thank You! ✨🦋
Gravitational waves are sometimes generated by objects that make a flash, like neutron star mergers. Perhaps we'll be lucky to have a telescope pointed in the right direction to measure if there is an arrival time difference between the photons and the gravitational waves, which are are presumed to propagate at c?
I was thinking the same thing!
This is EXACTLY was has been done since gravitational-wave observatories have been build like LIGO, LISA, VIRGO, GEO and TAMA. And what _"Multi Messenger Astronomy"_ is all about. You're a few decades behind 😉
And recently, after LIGO was upgraded and was started up again, they where able to detect such tiny differences in arrival time. But, this is an ongoing research. There are some preliminary results suggesting that there is indeed a time difference (and it isn't just a result of statistical error). But this is still so cutting edge that no concrete conclusions should be and can be drawn yet as there are also other explanations why such time difference is there.
Here’s a specific example: gravitational wave event GW170817 was a merger of two neutron stars. The merger also produced a gamma ray burst detected 1.7 seconds after the gravitational wave signal. The merger occurred in galaxy NGC 4993, about 140,000,000 light years away. If the difference in detection times was due to a difference in fundamental speed and not other factors, well, somebody check my math but that’s a factor of about 2.3 x 10^-15. If gravitational waves travel at the speed of causality, those photons got here at virtually the same speed.
@@josephatthecoop Thanks, somebody tell us what that equates to in Photon mass, if we for a moment pretend one measurement is enough and space is perfectly flat.
I think we would see the light arrive slower, but it really would only mean that the space the light traveled through was not a perfect vacuum.
Hi, Arvin. If photons have mass, then information about very distant galaxies would reach us before light from those galaxies reached us. But this can't be so, since the only way for that information to reach us is if its carried by light. So if information can't move faster than the light that carries it and light can't travel faster than information, they must move at the same speed and that speeed must be C. If only massless particles can move at C, photons must be massless.
Does not follow logically. It is possible that information reaches us via some other means before photons do. You only ASSUME that information about distant galaxies can ONLY reach us is by light. You do not KNOW that.
That would mean gravity is not information. Because gravity spreads at the speed of information, but in your example it must not contain any information.
@@pauloreilly782 what medium would that be? Information about distant galaxies must reach us through some physical medium. If not by photons, then by neutrinos (which we know travel slower than light) or by gravitational waves (which we have experimentaly verified travel at C), or by cosmic rays (charged partiles) which travel slower than C. The fastest speed that information about a distant galaxy can reach us is C. There are no observations or experiments showing information moving faster than C. If information about a distant galaxy arrived at a speed faster than C, how would we detect it? What physical, detectable, signal would we see? Information requires a physical medium to move from one place to another. In the case of information from distant galaxies, that medium is waves in the quantum electromagnetic field, carreid by photons of various energies and wavelengths.
All we can know about a distant galaxy (all the information we can gather about it) comes from what we see when we point a telescope at it. This has always been true. If you think we can receive information about a galaxy before we see it (even if light tarvels slower than C) show me this information. What does it look like if it wasn't carried by light? If the information arrives before we can see the source, how do we know the information is true? How can we even detect information not trasmitted by photons or some other particle? Check the flow of your logic and assumptions.
@@Jasmin-lg3gfGravitational waves travel at C. We've experimentally measured this with the LIGO detectors. Gravity does contain information, but it doesn't travel faster than C. Gravitons, if they exist (I think they probably do) are, like photons, massles and travel at C.
@@DeanBathaDotCom You just said that information from a distant galaxy can also be transported via gravity.
Photons are just one way of transmitting information. A postman can do that too and is much slower than c.
I watch so many science and physics type channels, but am today years old when finding an Arvin video in my recommendations
This is a great video 👍
Fascinating. And I'm quite surprised I understood this being totally hammered on an entire bottle of straight Jack Daniels.😂
I think they have to have an extremely small amount of mass. But that would destroy alot of dark matter dark energy hypothesis.
Yes, it might destroy dark energy hypotheses. I say that's fine.
Your channel is great, not so many people are willing to question current physics theories. My favorite on the site for many years.
he's not questioning current theories. There have been many experiments looking for a photon mass.
See: pdg lbl gov ..the current limit is m_gamma < 1e-18 eV
It never stops blowing my mind how there are so many equations people came up with that have made stuff so much easier for future generations. I’m always curious what people will come up with next.
In 1899 the commissioner of the US patent office said that everything that could be invented has been invented. The 1800s saw so many inventions that changed the world that he couldn't imagine anything new being discovered. Before the moveable type printing press brought on the industrial revolution, the world was seemingly static. Today we assume the opposite that there is no limit to what we can achieve. Hopefully we don't become a victim of our own success. Extremes in anything tend to revert to sustainability.
Nice work. Thanks a lot.
Thanks for this video. I’d never considered causality as being the max speed. Now can you do one on electromagnetic fields in 3 dimensions. they are always shown as 2d squiggles on a plane what would they loon like in 3 d and what effect would that have on the double slit?
Dont think they can do 3 d. Therefore no effect on double slit
If there was no massless particle(to test the speed on), would we be able to ever tell the actual speed of causality?
Not using particles 🙈
I think it would have to be pretty close to the speed of light, because even if photons were slightly massive, they would be so easily accelerated that they would travel at near the speed of causality at all times.
I'm curious too whether there's any theoretical framework that would give it to us exactly. I think the whole of relativity is much more complex than people present it, like obnoxiously big formulas with hundreds of distinct terms and effects, and I don't know much about it.
@yodools The question is if there is another way to test "information speed" other than measuring particle speed.
(Guess not if we tend to quantize everything into particles, possibly graviton)
@@amorphantthere are theoretical frameworks that give us it exactly. There are no *practical* frameworks. No matter how much data you have, theory always starts with an unproven assumption and carries forward from there. There are more than a handful theoretical foundations that take us to the conclusion that they are, in fact, exactly massless. But these starting assumptions can never be proven, only verified to increasingly fine precision.
Einstein setting light speed as the max speed limit of massless photons I think, neglect the energy packed in photon that has an equivalent in mass.
Maybe what finally gets inside the singularity is truly massless with no speed limit (entanglement speed) and what the falling particle can’t take in the singularity, will be visible at its event horizon once particle is bound to fall in; and it is the evidence we can examine which is what’s left in that last moment in time as the particles duality is left behind and the particle itself is massless and dimension less and falls into singularity.
That the speed of light is constant, that the speed of light is the fastest in the universe and that the photons are massless are all assumptions(scientifically unproven up to today). These assumptions have been around for so long that people forget they are unproven. Many scientist even ignore this fact. Very good point you make here ...
Another great explanation! Not many have covered this topic either, good to see some "non-standard condition" videos too.
How do you define causality or the speed of information? I always thought that the speed of light was inextricably tied to the speed of information. Absolutely love your videos, by the way. You remind me of my old physics professor at college who had your gift of making the impossibly complicated seem blatantly obvious.
Gravity is also assumed to propagate at the maximum speed.
Gravity propagates at the speed of light. That means that gravitons may also not be massless, however small they are. The whole point of the video is to say that the speed of light is not the maximum speed set by the universe, ie. the speed of causality or information.
@@spyrosspyrou5809 Gravitons are purely theoretical. But no, gravity is not assumed to propagate at the speed of light, it's assumed to propagate at the maximum speed. Since gravity is, for all we know, not transmitted by photons, there's no reason to assume it would also propagate slower if light was slower. It would be totally possible for gravitational waves to move faster than photons, which is something that LIGO and some of the other detectors are measuring, but so far without any results to this end.
Gravity is not 'assumed' to travel at the speed of light, it's a prediction by Einstein's theory of relativity.
So, if gravitational waves are proved to travel at the speed of light, then this would show that photons are, indeed, massless or that gravitons, if they do exist, have the same mass as photons. Personally, I have trouble believing that there is such a thing as a massless particle. If it has no mass then it can't be a particle and if it's a particle then, by definition, it has a mass. But that's just my opinion.
@@spyrosspyrou5809 Where exactly does Einstein posit that gravitational waves travel at the same speed as photons, if that speed does not happen to be c?
This is very intriguing and Arvin is talking about a very, very tiny amount of mass.
If photons had ANY mass, then shooting photons into a closed box should make it weigh more over time.
The merging of neutron stars creates gravitational waves which should really move at the speed of c (causality) if the light from those mergers arrives even slightly later that would mean Photons have some mass
Except for one problem. Light only travels at C in a perfect vacuum. Space is a very good vacuum but not perfect. Therefore the light arrives slightly later than gravitational waves
@@wingracer1614Also, it’s possible that the mass of the photon could be so minuscule that even a photon racing a gravitational wave across the entire universe still wouldn’t arrive at a different enough time to be detectable.
Or maybe it isn’t I dunno lol I’m not a physicist
Mindbending for a layman like me and not always easy to understand but nevertheless great fun. Thank for the amazing content.
You have been lied to and enslaved 👉 The Connections (2021) [short documentary] 💖
Ive been explaining this to my kids for decades, now, someone smarter than me, is explaining it to everyone. Thanks.
It's weird to find out that even though it's a good assumption, the idea that light is massless is still an assumption. One thing that has long confused me is how time stands completely still for things going at the speed of causality. That being the case, if there is no time, I wondered how things can even interact. I know that from our perspective, time passes, but from the perspective of the massless object, time does not pass so I would assume that there could never be an interaction. If light traveled extremely close to the speed of causality but not exactly on it, then if a photon traveled a billion years across the universe and interacted, maybe from its (non-sentient) perspective, a millisecond would have elapsed...but that would still be enough for it to have traveled and interacted, whereas a permanent pause of time almost seems like it can't lead to anything.
Has anybody actually confirmed that that there isn't a tiny dragon that carries the photon and prevents us from measuring its mass? It could also be really small and difficult to detect but we can't really say it's not there either
I think we call that dragon Dark Matter.
You sound like the tea pot around Mars and invisible unicorns and flying spaghetti monster jokers who hate on religion. Whether we're talking religion, or science or something else, at some fundamental level eventually you must take things upon faith. Yes, even with science. We're assuming that all we see or otherwise detect in experiments is really there and not an illusion or simulation every time we make an observation for some experiment. Who knows, there could be a very small dragon carrying around each photon. Heck, for all we know it is just the same tiny dragon for each photon but this dragon is either omnipresent or travels at a much faster velocity than light to be able to carry around all the different photons.
What a load of BS. Dragons aren't real.
Everyone knows it's a really tiny clockwork elf.
@@RJ-rf8fu Woah woah woah, I thought the tiny clockwork elves lived in the atom's nucleus, aka the Keebler Houses. I thought they sent out their tiny dragon pets to deal with electron-magnetic interactions, photons, etc, you know, like guard dogs.
@@Tletna : Oops, yeah, my mistake 😆
Thank you Arvin for diving into this, i’ve been wondering about this for years and I have never found any experiment to prove it’s massless. Yet every textbook says its massless like a fact. I always thought this was strange. Thanks for this video showing my observation is not insane.
Reason why I wondered about this, is if the photon had a slight mass, it would be just below the speed of information, which means time does not stop for it. But the inverse I always thought was strange with a massless particle. Its perspective would be instantaneous travel since as you approach the speed of information time slows down. At the speed feels like it should be undefined, yet slightly below seems more realistic.
You're wrong
@linguae_Music No, infinite energy would only be true if photons traveled at the maximum speed of the universe. A massive photon would not be traveling at the maximum speed. This means that the measured speed of light we know of today would not be the maximum speed that was possible in the universe. That was a big point I tried to make in the video.
@@ArvinAsh Don't observations we can make depend on c being the value that it is rather than something slightly higher?
@1024det "Matter tells spacetime how to curve, spacetime tells matter how to move"
The key for understanding that aspect of GR is that it isn't referring exclusively to space, but movement through *time*
Massive objects limit the "flow" of time. Relative to a photon, yes it would be absorbed instantaneously. But massless particles aren't the only objects defining spacetime curvature right now, and photons are subject to the same spacetime curvature as other objects :)
@@clocked0 The value we use for c is the speed of light. As its assumed c=speed of light that we measured most accurately as we can. In the paper Arvin sited is a list of the actual measurements. In there the most conservative (smallest mass possible) is 3 x 10^60 as its upper bounds.
Arvin is simply saying its more accurate to say c >= the speed of light since its possible a photon could have mass
My conjecture is the photon has oscillations similar to neutrinos. Only the photon does not oscillate in type and mass, it oscillates through E-field, B-field, and for the briefest time interval imaginable having mass. In effect it propagates through space as fields but is "localized"while it has mass.
So it moves through space like a dotted line.
Wow sooo cool. Thanks AA!
I thought that the lack of mass of a photon was what allowed its speed to remain constant in all frames of reference. If the photon had a mass, would that mean its speed differs for different observers? Would there be some side effects of this we would notice when looking at, say, high speed matter accelerated by the gravity of a black hole?
If photons travel slower than c, we must ask relative to what?
Relative to the source of the photon?
If that is the case, could we observe the difference in arrival time of photons from a very distant explosion?
@@bignicebear2428 if photon travels slower than c, it would travel slower than c relative to anything (i.e. in any inertial frame of reference).
@@Drazzz27 True but by how much? It no longer would be the same speed for all observers.
If relative to the source, there would be photons travelling at different speed through vacuum, which could be detected.
If relative to the intergalactic medium, that would be no different than the very thin hydrogen gas having a refreaction index not exactly 1.
If relative to the observer regardless of source, not sure how that makes sense.
@@bignicebear2428 well, the only thing that matters is whether its speed distinguishable enough from c in our frame of reference to notice any accompanying effects.
In theory, photons with mass would indeed travel slightly different speeds in different reference frames. This is just one of the many ways we know for sure that photons can not have any significant mass because if they did, we would have seen that difference by now. If they do have mass, it would be so tiny that we would probably never be able to measure any such differences. This is why it's perfectly valid to treat photons as massless even though we can't totally prove it. The difference isn't enough to make a difference.
Doesn't a massive photon break some gauge invariance? Cant remember...
I just shone a torch at my kitchen scales, they didn't move, so no mass for Photons.
WOW! This guy never disappoints.
I've seen neutrinos having mass explained as a result of them experiencing time (because they change flavors during their lifetime), but photons in an expanding universe seem to also change due to cosmological redshift; I.E. the longer a photon exists, the longer its wavelength. Could that mean that photos experience time and therefore have to have mass, however small it may be, similar to neutrinos?
The redshift doesn't occur because of it's age though.
Photons is waves and redshift is change in wave length due to the observer moving nearer to it or from it, just like the sound of a train horn passing by changes frequency...
@@a64738 I'm not saying you're wrong. In fact, you're probably right overall. However, collisions in air that produce sound waves are more classical, with them moving past observers at different rates if the observer is moving. The speed of causality, however, is seen the same by all observers, no matter their velocity. So it's similar to, but not just like the sound of a train horn passing by that changes frequency. It may well be that the redshift is fine as is, without light having a mass, but I just wanted to point that out.
I wonder what the minimum frequency of flavor change for a neutrino is as measured from it's frame of reference? Given, the best measurements we've made give an upper limits for deviations from light speed of approximately 10⁻⁹ that could be rather high. OTOH, given the quantum nature of a neutrino, I'm not sure it's even meaningful to ask questions involving extreme cases in GR; QM and GR tend to not like working together.
@Rationalific actually he's pretty spot on, Google how laser cooling works (they use a laser with very high coherence, at a frequency just below the excitation frequency of the thing to be chilled, if it's moving towards the laser then the frequency appears higher and the object becomes excited, emitting a new photon in response, however that new photon now has a higher frequency than the one absorbed, as a result of conservation of energy this results in some of the object's kinetic energy being lost to the new photon, cooling the object).
However generally redshift is described as the spacetime the photon is traveling through itself stretching, stretching the photon within it along with it, thus increasing the wavelength of the light. If the spacetime itself is what is changing then the photon doesn't really need to experience time (as this isn't a change WITHIN time, it's a change of time and space itself). Ofc that explanation relies on spacetime fabric actually existing, which is another unproven thing (PBS spacetime ironically has a vid about that). If spacetime doesn't exist however then gravitons (or their like) must exist, as gravitational forces must then be mediated by something.
Super interesting. I think I would never be tired or bored learning physics. This is me even when other people think I am a strange person. Life is so short. Thanks RUclips and Arvin for keeping the light on for those who love physics and other subjects. This generation and next will have the privilege to learn so much about things before deciding what to do in their life as a career or as a hobby.
At some point it's possibly gonna end, though. That's kind of a philosophically naive statement not without controversy, but I think it's fair assumption.
Nah man, we are just listening to nice parts of Physics. Once you do something on a daily basis, it becomes a job and down the line, it gets harder and harder to have the same motivation.
@@liquidmetal718 yes agree 👍👍 however it feels good knowing there is logic and a some sense of order within the caos in the vast of the universe.
You have been lied to and enslaved 👉 The Connections (2021) [short documentary] 💖
I had a professor in chemistry say it is a wave that acts like a particle because if it had mass it would leave something behind when it hits an opaque object. Then he went on for ten minutes asking if radio waves have photons and on and on. I guess he had a grudge against photons. I took notes because his exams would include things like light as if Organic Chemistry wasn't hard enough.
I was intrigued about the magnetic reference.
Cool video as always. Could light not travelling at the speed of causality have anything to do with the double slit experiment?
Would that make the photon experience time, and begin to gain mass?
We know that gravity does affect light,as seen with black holes,so sure photons must have just enough mass to be pulled in but not enough to be detected. Of course I'm not a physicist so i could just be way wrong here😅
As I understand it, gravity is not a force and does not pull on or attract any object.
Rather objects, including light follow a straight path in space, but space is curved by and towards large masses such as stars etc.
Gravity is the name given to this phenomenon. Of course I'm not a physicist either.
After hearing about the different velocities of light for different wavelengths due to a photon mass, It is clear that all the evidence points to the photon having a mass. Specifically, the evidence currently of us measuring two different hubble constants with two different methods (CMB vs standard candles).
Everything we’ve ever assumed was broken so I’m going to say that photons do have mass and causality is the true speed limit. Intuitively, as a non physicist, that makes more sense.
Hypothetically, could massive photons cause tired light and red shift?
That sounds reasonable.
They do and it definitely gives the illusion of the universe expanding.
No.
@@dukeon 🤣
I hope I can do my PhD on how photon carry so much data/information when it bounces off an object and hit our eye/vision system.
It should not be a PHD, single photon do not carry any information. It act like a bit in the computer. Present or not present. Here is a task for PHD. Mass of a photon have to mass equallant of energy plank's constant h. Electrons allways emit h regard less of frequency. But it never multiply for it's velocity C. Find out what's happening!
@Dxeus
consider this: a photon never "bounces of" anything. That is just a simplification to easily explain some other things where the true mechanics of how light _"bounces of"_ something doesn't really matter.
In fact, the photon's energy packet is absorbed by 'the object', and in turn 'the object' emits ANOTHER photon (with a slightly altered energy packet). It is NOT the same 'thingie' that simply _"bounces of"_. It is a different 'thingie' all together.
What about polarization? A spin-1 vector boson has 3 degrees of freedom for polarization, but if it's massless it only has 2. If light had 3, wouldn't it be easily detectable?
If I remember correctly, light is electro-magnetic wave. And a guy, called Maxvell, find out that the speed of this wave is c=1/sqrt(e0*mu0). Well... no mass in equation. Only properties of vacuum. If you want to change c - change vacuum properties
Just a thought, if photons have mass, then quantum entanglement could be an example of the actual speed of causality. If for instance quantum entanglement has a definable speed that is simply too fast for us to measure.
I thought of that too but quantum entanglement seems to be instantaneous.
@jonwesick2844 maybe we just don't have the means to measure it yet
your comment , if correct , would explain A LOT. Quantum entanglement has alway bothered me. Your thought makes a lot of sense.
@@jonwesick2844perhaps it’s faster than we can measure ?
The speed of causality is still c, light having mass merely means that light doesn't quite travel as fast as c. Calling c the "speed of light" would be inaccurate, that's all that would change.
The video already discusses this at the 3:13 mark.
So the obvious question is, is it possible to thread the needle? Can photon Mass be low enough individually to avoid the effects you describe yet sufficient that in the aggregate it can add up to something? (I am of course thinking of dark matter, mostly because the ten year old boy in me would giggle with glee at the idea that dark matter might be composed of literal light.)
Maybe if the entanglement only is truly massless...
And photons with extremely low mass, practically zero, but not exactly?
Interesting thought. I like the idea of if a photon has mass that is related to it's energy, dispersion would occur with gravitational lensing. I always assumed since a boson cannot interact with itself, it has to be massless.
The SM Higgs is a boson that interacts with itself. The theory can not rule that out. In the current version of the SM all fields are massless until we turn the couplings on, so that's not helpful, either. One is simply hitting the limits of the math at this point. The current theory has a very poor structure with regards to the interplay between free and coupled fields. It works at the scale of accelerator experiments as an effective field theory, but it's not clear how it would work at the scale of the full universe.
For someone very curious but not professionally involved in the deeper workings of physics, it would make a lot more sense if light was not travelling at the actual speed of causality. Cause we could think of it a lot more like we think of sound. Just like sound has it's speed limit via the medium it travels in, it would make sense that light had it's limit via the medium / field it travels in, rather than something as intangible as causality to pose an arbitrary limit.
I imagine that when light had mass, the devs have seen the graphical artifacts and fixed it by setting the mass of light to 0. Maybe it's also easier on the hardware of the simulation by setting it to a constant, who knows. Maybe check the devlogs.
They stopped letting us read them after that one incident with the room full of metronomes and the spinning squirrel.
If light is electromagnetic wave, are all radio waves photons too?
Yes indeed.
Photons and radio waves will go through glass. Radio waves will go through card board but photons will not. I guess it is just one of those things. 😊
As you have said- we do not observe lack of low energy photons from far away regions of space. That doesn't mean the photon may have very small mass. The distances are so long, that any difference in mass would produce large observable differences in photon arrival. Einstein rings would be like rainbows(separation of photons by energy). Also it would be impossible to observe far away objects not only because of different arrival of photons, but the telescopes would be unable to focus- we would use filters to get rid of different wavelength photons first. This all is not happening at all.
Great Video. I'd love to get a better mathematical understanding of why massless particles can only exist travelling at the maximum speed c. Any chance of doing another video that goes into the maths a bit deeper?
a massless particle traveling at less than the speed of light would result in a violation of causality (and create a host of other problems)
@@Mutrino i'm sure that you're right. Show me the maths.
@@HighWycombe The wave equations derived from Maxwells equations would need to incorporate a mass term, this would introduce a frequency dependence that contradicts experimental results. Again, the masslessness of photons is well established and supported by experimental observations
How would time be experimented inside a black whole where light blends and never escapes? Could several photons from different events reach your eye at the same time? What image would that provide?
Arvin, your videos make me regress to that stage of childhood where one asks questions non stop. lol Thank you for making my mind wonder!
Temperature and surface gravitation (gradients) are a substitute for time. A black hole inhabitant has something similar to cosmological time. They would see "their world" shrink slowly and cool until nothing was left. At least that's what the theory suggests. In reality we will probably never know unless we can find ways to invalidate and replace GR as the effective field theory of the black hole interior.
@@schmetterling4477 @yasmin-pi5pr That is interesting to think about… As I consider this, I realize that the answer should be no, you would not see several photons at the same time. Everything inside a black hole has crossed the event horizon on a path of spacetime which is curved at faster than light speed. Therefore, everything which crosses the event horizon will be separated by some arbitrary distance and will require faster than light speed to catch up to anything else which has already crossed the event horizon. Atom by atom, photon by photon, all things crossing that horizon are moving faster than light within spacetime, so no atom or photon can ever come in contact with any other atom or photon. Everything in the blackhole must be completely disconnected by another type of horizon. We’ll call it a “light speed horizon” if you don’t mind. And the light speed horizon would act on everything inside a black hole such that nothing can escape its own light speed horizon. Things going into a blackhole can never obtain the energy to escape the gravitation, but also it seems that things going into a blackhole may never obtain the necessary energy just to catch up with the surrounding particles, photons and other blackhole inhabitants.
Hi darling I love you 😊❤
Assuming that gravity continues to behave similarly as it does outside an event horizon, that light you ask about wouldn't be able to travel to your eye from anywhere unless your eye is between it and the most direct path to the densest region of the black hole, it's center. So to see anything inside a black hole, the light source the object and observer would have to have relatively stable positions inside a singularity on the shortest path from the light's entry to the center of mass. Light would behave more like what you are used to seeing water or sand do on earth, it'll be pulled to the lowest available area and flow there freely.
@@warpdrivebyvery visual the comparison to water, thank you for the explanation!
If there was a way (there isn't; special relativity prohibits it) to observe a photon at rest, you would find it massless. All the relativistic mass of the photon comes from it's energy. In particle physics when we say mass, we usually refer to the rest mass. This is why we usually say that photons are massless.
If there was a way to observe a photon at rest, we would measure it to have mass, since only objects with mass can be observed at rest.
Did you watch his video, at all? He clearly states the mass of a photon (if there is any at all) is so small that our current experiments cannot detect it. This means we cannot prove that light has mass or no mass. We don't know if it does or not, just that it must be small if not zero. Considering all particles except for maybe gluons have measurable mass, why would light be an exception? I'm not saying that I believe light 100% for sure must have mass (rest mass) but it would explain a lot of things if it did.
One point: We talk about 'rest mass'. And there is NO photon "at rest" ...
Shouldn't we assume that photons have mass since light is affected by gravity. Also, photons can transfer momentum, making solar sails possible. Both of those phenomena would suggest the photon has mass.
Gravity is nothing more than gradients of time. Photons are simply taking the shortest time path through space, like everything else.
As per my understanding, light photons simply follows the curve path of space time, distorted by gravity. Light photons do have momentum but no rest mass which makes solar sails possible.
They say gravity affects light only because it bends the space-time itself, not the photons of the light.
Yes. Photons have mass like liquids. Mass (m) becomes Energy (E) as E = mc^2. But if the speed of light depends on the Density of Vacuum Space (DVS), it would impact the speed like this: 'the speed of photons' / 'the density of space' = 'c^2' / '(DVS)^2'. The mass density of space is most likely equal to this: 'Mass of space in a Planck volume' / Planck volume. We can apply the mass density of space ((Mass in Planck space)/ℓp^3) into the E = mc^2 equation to show the connection between the speed of light and the density of space. If we write the mass in a Planck volume like this Mps/ℓp^3, we can find the energy like this: E = m(c^2/(Mps/ℓp^3)^2). There are kg^-1 m^8 s^-2 units in that energy equation. The kg unit in energy turned into kg^-1. Momentum is related to Mass, but the momentum (p) in the E=pc equation doesn’t represent Mass. So perhaps, the Energy per Kilogram (kg^-1) unit with m^8 s^-2 units represents the fundamental (quantum) units in energy better than kg m^2 s^-2 units. c = 299792458 ms^-1, ℓp^3 = 4.2217×10^-105 m^3
E = m(c^2/(Mps/ℓp^3)^2) OR ((p+mv)/v)(c^2/(Mps/ℓp^3)^2)
E = m ((c^2 / (Mps / 4.2217×10^-105)^2) == mc^2
(1 × 4.2217×10^-105)^2) / Mps^2 == 1
Mps^2 = (4.2217×10^-105)^2
The current mass of vacuum space in a Planck volume: Mps = ±4.2217×10^-105 kg
If m=0, and E = ((p+mv)/v)c^2/(Mps/ℓp^3)^2, then E = (p/v)c^2/(Mps/ℓp^3)^2. If v=c, then E = pc/(Mps/ℓp^3)^2.
If momentum is nearly equal to zero (p=0), then E = mc^2/(Mps/ℓp^3)^2. But Mps/ℓp^3=±1 kg/m^3, so E == mc^2.
If Energy (E) = kg^-1 m^8 s^-2, then it must be consistent with the other units. There are extra dimensions in that energy. Also, there are extra dimensions in Volt as kg.m^2.s^-3.A^-1. The Ampere (A) is the base unit of electric current. V = J.A^-1.s^-1. The Joule (J = kg.m^2.s^-2) is a derived unit of energy. Hence, if the Volt (V) = kg^-1 m^8 s^-2, then kg^-1 m^8 s^-2 = J.A^-1.s^-1 = kg.m^2.s^-2.A^-1.s^-1.
kg^-1 m^8 s^-2 = kg.m^2.s^-2.A^-1.s^-1
A = kg.m^2.s^-3 × kg.m^-8.s^2 = kg^2.m^-6.s^-1
If the Ampere (A) = kg^2.m^-6.s^-1, then kg^-1 m^8 s^-2 units for Energy become consistent with the other units.
Velocity= v = L/T. Momentum= p=mv. If, Kg work = m^3 =ℓp×ℓp×ℓp, and potential energy = pc, and E =(p/ħ) × cħ, then E = (mv/ħ)cħ = (ℓp^3 × L/T × c × ħ)/ħ. But if ħ = HWD, then energy E = (ℓp^3 × L × c × HWD)/(ħT).
E = ((ℓp^3)/ħ)cLHWD/T or E = HWD((ℓp^3)/ħ)c^2 kg^-1.m^8.s^-2 while ħ = J.s = kg.m^2.s^-1, or:
E = ((ℓp)/ħ)cLHWD/T or E = HWD((ℓp)/ħ)c^2 kg^-1.m^8.s^-2 while ħ = kg.s^-1. So If, D/ħ = 1, and mass = m = HWℓp, then: E = mc^2 kg^-1.m^8.s^-2 (m is not in Kg. m = the volume of the mass = 1×HWL/mass m^3.kg^-1).
Force (F) = the amount of volume relative to the mass × acceleration = n×(HWL/1kg)×a. So, E = n(HWL/1kg)c^2.
The E= mc^2 equation is wrong if energy is an accelerated expansion of a volume. A force/F is a linear acceleration. And a force is massless too.
Photons have momentum. Mass is not necessary. Gravity affects the space-time surrounding the photon.
I am continuously slammed for offering alternative theories for our reality. Typical reply is *_"Read a frickin' physics book before commenting!"_* ... And now here we are in 2023 discussing whether or not a photon actually has mass.
Sir if you get time,please make a video on why elements in main group follow octet rule.
It may be helpful also to make a difference between the phase velocity and the group velocity here.
"Speed of information" vs "speed of light". That's a key difference we don't hear often. Looking at things with this mindset helped me easily digest the fact that photons needn't be massless and yet we don't violate relativity or other known laws of the universe.
Thank you Arvin for making another great episode. You truly are a gifted teacher!
Plank time should be the limit on speed of information.
@@eleventy-seven Why? Did you see how it's defined?
Seems like circular reasoning. E=mc^2 *because* photons move at c. And photons move at c *because* E=mc^2. How does that make sense?
All of existence, including photons, is massively strange.
There have been several measurements via LIGO observations that confirm the speed of gravity is == the speed of light. The simplest common denominator would be that both gravity and light carriers are fundamentally massless. Even though no gravity boson has ever been detected, w/e the carrier of that force is, is working at the same speed as light.
Thanks Sir 👍
If light is massive and traveling so incredibly close to the speed of causality, then the inertia of a photon would be so high, it should be nearly impossible to change the direction of a photon. It should be nearly impossible to reflect light. It is basically the easiest thing to do in the world - to reflect light… so light must have extremely low inertia even while traveling at almost light speed, or has absolutely no inertia at all.
Thanks for the video. So what part of the photon is captured by a black hole?
Food for thought:
Define "mass" m0 such, that m0 is the minimum (objectively measurable) energy of a particle of a given type (at the present time).
The energy E of every (measurable) particle is directly related to the de Broglie wavelength lambda of the particle.
Lambda can be regarded as a measure for the particle's spatial extension.
E = m = 1/lambda (in appropriate units).
The largest (measurable) (wave)length is the "current size" of the universe r (or rather, the distance a photon will have travelled within the entire age t of the universe, e.g. r = t).
lambda_max ~ r = t ~ 10^61 (in Planck units).
The largest measurable (de Broglie) wavelength gives rise to a minimum (objectively measurable) mass-energy E_min = 1/lambda_max, so that
E_min ~ 10^-61 (in Planck units)
This means
m0_photon >= E_min ~ 10^-61 (in Planck units)
Likely the photon is the particle with the smallest possible (rest) mass within the (observable) m0_photon ~ 10^-61 (in Planck units).
This is pretty small and not measurable with current technology. In fact, it would be the minimum mass-energy measurable with any technology.
Dear Dr. Ash… thanks for making this video and addressing this issue. Just because we don’t have precise or accurate instrument to measure photon mass should not suggest photon is massless. Based on observations, light or photon does suggest mass. Example number one, photosynthesis: light carries energy, so filtered light excites the electrons state to begin synthesis. This is consistent with the equation e = mc2, because m cannot be zero to have energy. This would also explain why any light source is also the energy source for plants to fix carbons. Second momentum p = mv… a massless object cannot have momentum, and photons clearly do display direction and momentum. Finally an added observation; using a magnifying glass experiment, light behaves similarly to water in a narrowed hose. This also suggests a fixed amount of particles colliding faster. We can easily measure water and velocity. The magnifying experiment suggests photons in a smaller space colliding against each other, so these photons should have mass. However, maybe not in a traditional sense of neutrons plus protons to give mass, but something else. Photons definitely display mass like behavior. Those are the observations, and everything points to a tiny mass for photons… because e = mc2 is consistent as how we receive energy from the sun. That would be an educated guess based on observations. Photons mass, if it exists, could challenge our perception of reality, because it could exist in dimensions, but not in time. Photons could be a multi dimensional particle or quantum particle… which can exist in many planes. We currently cannot measure its mass because we are thinking single, two or three dimensionally about light, but what if it is much much more. As you pointed out a visible light carried ROYBGIV spectrum, and these wavelengths contain energy or e = mc2. How many energy states does light really carry and which dimension does light hides them in?! To break the code of light sound like the next evolution in physics. Thanks for making this video again… please let us know more on photons, thanks
I wish you'd made a much bigger deal of just how "almost sure" we are that photons are massless. This is the same "we don't really know" that lies at the bottom of _everything_ in science, simply because science, as a philosophical construct, can never have 100% certainty about _anything._
The chance that photons are not massless is extremely small. At least, real photons. Virtual photons can and do have mass, sometimes quite high, but those are only a mental construct to help us make sense of a universe that doesn't actually seem to have particles at all.
That lower bound on photon mass is _absurdly_ small. I'm guessing it comes from something like the limit at which the prism effect would be seen, or possibly the timing of the arrival of light and gravitational waves of that supernova a few years back, which also puts any potential difference between the speed of light and the speed of causality as exceedingly small as well.
I agree to the notion that the speed of C is not necessary the speed of causality, as for the mass of photon, there's a huge gap of understanding that needs to be filled.
It's well established that it would take ABSURD amounts of energy to move an object with mass at the speed of light
Correct.
6:35 We do have another experiment - LIGO. Specifically we can compare the time of arrival of gravitational waves against the time of arrival of the incident light when an event occurs that produces detectable wavelengths of both, such as the semi-famous GW170817 neutron star merger.
Now that doesn't in itself prove light is massless, but if it does have mass, the speed reduction must also be reflected in gravitational waves to very high precision. Somehow.