A Photon has no mass. It can’t rest. Reply

A) A Photon has no mass. B) A implies “It can’t rest”. C) Therefore it doesn’t have rest mass. D) Photon rest mass is zero.

Assertion and reasoning; A is correct. B is correct and follows from A. C is correct, it does follow from C. But D is incorrect it does not follow from A, B, or C. Its erroneous, a sloppy language that has been thought to be correct for ages now.

The trick is to realize there is no property called mass of photon — at-least in the same sense as it is for other particles with mass, therefore no rest mass. To say rest mass is zero is a special value of mass or rest mass. It just doesn’t have rest mass, as it neither has mass, nor rest, which are equivalent formulations, one leads to other. But A, B or C do not lead to D. They are not equivalent way of saying each other. They invalidate each other actually.



When I made a presentation on why we shouldn’t call photons mass a “zero rest mass” I was thinking we make such mistakes only informally until just couple minutes ago the above texts flashed across my rest seeking eyes. (– or check this one, there are also some other articles that talk about this idea, after I realized my mistake years ago, but perhaps they are in terse form, and will be revised upon availability of time and a priority)

This is at-least the 4th mistake I have spotted in text books in recent years. Other mistakes I realized as my own mistakes or of others in discussions.

I have made this terrible mistake of calling photon mass as a rest mass just like the authors of this text book. Photon just doesn’t have mass.

(Its fine to say photon has zero mass, but not fine to say photon has zero rest mass, just don’t use the rest term, it causes photon to smirk at ya and say look you don’t understand me, okay, so just bugger off)

Because it doesn’t have mass (from which it does follow, it has zero mass) photon flies off always at same speed, hence no rest frames. v=0 is not possible for waves called light. v=0 is possible for particles with mass. A mass-less particle is an extended region as its a wave and one cant wish a velocity for it as one can for particles with mass. Zero velocity for such extended regions with other conditions is out of consistency.

One should also remember E=mc-square is not valid for photons. Its valid for particles with mass only hence for processes involving photons and other particles but thats because particles other then photons have mass (and energy) but photons have energy as well (but no mass) and this energy is consumed or released by other particles (such as pions or electrons). All in all due to energy conservation E=mc-square is valid, but not for photons alone.

This book is one of my most favorite book at junior coll level, a brilliant piece otherwise. Written by highly qualified professors from Ivy leagues and the likes, but such errors have persisted from ages. This book was ” originally ” written in 1970s — A decade before I saw light of the day for the first time_ first used by me, 20 years ago, I was 17, when I was yet to be qualified to comment on Relativity.

Its a widely used textbook and admittedly one of the best and most brilliant textbook at this level. University Physics originally by Young et al.

Interesting Physics facts one would love for ever Reply

Interesting fact 2; Give an example of a motion where when we apply a force on the object, the force produces motion of the particles along its own direction, the speed remains finite but does not change. According to F = ma, Newtons laws are valid for the motion but speed remains constant, while F is there, v does not change.

Since a = 0, with nonzero F and constant v, one could see this as a diversion from particle mechanics as formulated by Newton, towards a higher understanding, one could argue this as a great inflection towards Quantum Mechanics.

Also note that we are not talking about circular uniform motion where F does not change v, but there is non zero a. F is transverse to particles motion.

Interesting fact 1, certain forces do not obey any of Newton’s laws, in either its strong form or week form. Magnetic forces unless generalized suitably do not obey any form of the Newton’s law, strong = strict, week = partly strict.

Some discussions on fact 2

Would a quantum of charge in a potential changing energy levels occur without acceleration? I’m not sure if elementary particles change velocity instantaneously or do they accelerate.


Elementary particles change velocity if they have mass. — If they have mass, they have rest mass.

Photons on the other hand don’t have the property called mass. — So its erroneous to say Photons don’t have rest mass, they just don’t have mass, saying they don’t have rest mass would mean; they have zero velocity in some frames, which is physics wise unacceptable.

So elementary particles except zero-mass particles such as photons, change their speeds under acceleration. “Potential changing energy levels” simply means there is a force and acceleration, hence change in energy, speed, momenta etc of the elementary particle such as electrons in orbits.

— Their quantum numbers are different for different orbits, hence, energy and velocity etc are different. In the orbits the electrons would fall down to a smaller radius if they were to lose energy.

Since they are wave-particles we are talking about average values of radius, which decreases accompanied by some acceleration. So the answer to your query is YES, there is acceleration of these particles, in orbit changing processes. (excitation or de-excitation)

The above point of mass-less particles and particles with mass is what classically separates them as waves and particles. — mass-less = wave and particle otherwise. And speed is a variable if particle mass is non zero and mass keeps on changing as well. But zero mass would mean mass and speed are constants.


So in short waves; speed and mass are constants. mass is zero. speed is constant and finite.

Particles; mass and speed vary from zero towards a finite value as decided by the wave (above).

These are elementary particles and waves which come under two categories; matter waves (such as electrons) and non-mechanical (or em) waves such as (photons).

But the hints to my question lies on considering yet another category of waves viz; mechanical waves.


Happy Diwali ! Reply

A very happy Diwali to all my readers and all those who I can’t directly wish so considering the vast gap that technology can still not measure up in connecting us all physically.

Diwali or Dipaballi as well know is an Indian celebration in the month of November although the dates might alter to nearing the months of October or December considering the fact that Indian vernacular calendar is measured wrt the motion of moon and not the modern solar calendar which is most precise for mos of civilian time measurements on our planets. That simply means celebrations such as this might alter to weeks if not months altogether. I don’t have a data centric information regarding how much Diwali alters though, in terms of a Julian Calendar.

Thankfully much of our important transactions are based on the sun based calculations which means, in modern times, a great deal of corrections coming from the sidereal constants of motion. A sidereal constant of motion refers to having to fix all references wrt to distant stars so that fluctuations coming from sun or Intra-solar objects such as planetary perturbations itself can be properly accounted for.

Now coming back onto the idea of Diwali I am not going to delve into how much we want to signify it as a victory of morality over evil, and how much myth is important in our philosophical and existential moorings, such as how a monster by the name of Holika — gender specifically the feminine form of evil was killed by Sri Krushna.

I never like to take exceptions to how much vilification outdated traditions of our heritage and culture entails, and robustly establishes into a modern and civic society, which aims to be progressive and free from malice at the same time. The reason is I never see much intellectual debates that are free from wishful thinking and hypocrisy on one extreme and blindfolded adherence and a ready to die or kill attitude of the right wing inclinations in support of the veracity and usefulness of such traditional ‘wisdom’ and folklore. More…

Photo Credit and copy right; mdashf, Invariance 

Be simple; so simple that you can't follow in love, just like a simple drawing does not.

He is so simple he does not fall in love ! Reply

I came across the following wisdom from one of the revered religious Gurus of India, Swamy Paramahansa Yogananda and twisted it a little to fit my humor.

Be as simple as you can be; you will be astonished to see how uncomplicated and happy your life can become — Paramahansa Yogananda.

— This drawing is so simple it does not fall in love. More…

Photo Credit; www.slate.com

Aurora Borealis or Northern Lights at Ireland.

The Maxwell’s Equations, from nature to instruments. Reply

The beauty of Maxwell’s equations can be seen in how it helps us understand nature as well as instruments, at the same time. Medical devices are simply an advanced understanding that began with understanding electromagnetic waves through Maxwell’s equations.

Each of the following 4 equations has a different name, by which we call’em, but together they are called as the Maxwell’s equations. Together they constitute what I am inspired to say; the golden equations of Physics. If we do some easy tricks they will be converted into whats called as the Wave Equations (of motion) ! Yes, they describe the wave behavior “fully”.

— By that I don’t mean sound waves, but any sort of waves that move at the speed of light. Sound waves are ordinary pressure oscillations, that travel much slower than even rockets.
The 4 equations therefore describe how electromagnetic waves are created and broadcast. Hence TV radio and satellite communication were understood because these 4 equations were understood.

First two are time-independent or static equations.

The first equation is known as Gauss’s law of electrostatics and says “Electric fields (E), are a result of sources of electrostatic charge”.

The 2nd equation is analogous and called as Gauss’s law of static magnetic field. But it says “apparently there are no sources of magneto-static charge or single magnetic pole from which the magnetic field B is created”.

Then how are magnetic fields created? We needed to know further to find the answer. Lets look at the 3rd and 4th equations. More…


What I criticize and what I don’t? Reply

Previous title; Who I criticize and who I don’t?

Casual heroes and heroins and their ripened silence and immature hypocrisy.

Friends this is a general comment of the purported political nature of some of my criticism posts — on social media, which consists, mainly, G+, twitter, FB and occasionally my own website, and these type of criticism is only perhaps 10%.

I am not keeping a tab of the composition, but if I post a link of some discovery or some events, that I do not follow myself greatly, but just want to share, I do so, and that perhaps covers more significant numbers of my posts, on such social issues. Also more than 75% of my posts are perhaps simply neutral from a preposterous political view point. See what I mean, here, here and here.

So my own criticism may be significant, but I share a lot of views and opinions and analyses from others. This is also a modus operandi of how and what I am willing to believe, as opposed to what party line I would lick with impunity.

There are tons of events or news from here and there and only few involves important issues, that are being discussed elsewhere. If you are one of my regular post comment-er I would take your comments with as much sincerity as they are made with. In other words my alarm bells would not be ringing “caution”, I have already some kind of trust working between you, my reader, and me, the post maker.

But a one time comment that simply picks up on a particularly psychic paranoia of one self and projects as a generic nature of my existence, may not be seen with much impunity. More…