How can a photon have momentum?

Physics students often ask how it is that a massless photon can have momentum. In this video, Fermilab’s Dr. Don Lincoln shows that the question arises from a misuse of equations and also shows that, when you think about it, it’s not surprising at all.

Why E = mc2 is wrong:

The origins of mass:

Further reading:

Fermilab physics 101:

Fermilab home page:

[sbwhddv]

Thank you for all you do. Please NEVER "apologize" for including math in your videos. We WANT the math. Just be sure to explain what arcane symbols mean so those unfamiliar with those symbols can understand.

[alimuchenik]

I came across this channel just right now. I'm 67. It's soooo beautiful!!! I can't stop crying. There are so much cool stuff to learn and my time is almost up...
Blessings!!!❤

[beardedchimp]

I absolutely loved this. I started my undergraduate in Manchester 2005, and probably the most important lesson I took away was that these top physicists were incredibly humble and willing to say they don't know, or that they would need to look into it more before answering. The general public has this misconception that professors are arrogant, certain of themselves, and think they know everything. Nothing could be further from the truth.

The most common sentiment was everything is more complicated than it looks, we don't fully understand even if we can measure and model it fairly accurately. That as you said at the start, the intuitive explanation, even after decades of their research and study is still not all that intuitive.

Much of the general public dislike the fact that scientists won't give absolute predictions and answers, they demand certainty and dislike the unknown complexities. But physicists love that uncertainly, they love how strange and counter intuitive the universe is. If reality was just Newton's laws et. al the world we find ourselves in would be so boring. Instead we are confronted with something strange which when we begin to understand we unearth beneath strange layered on strange on top of strange. It is truly beautiful and fun. I'm glad I wasn't born into a time where we truly knew everything.

[novakonstant]

Excellent video as always. Fermilab has always been one of the coolest youtube channels out there. Thanks Fermilab and Don for making science more approachable for everyone!

[SkorjOlafsen]

I've missed these. These videos are always so well explained.

[Naked_Snake]

I'm so glad I found this channel by chance. First I was trying to understand refraction of light and now I'm trying to figure out if mass is even real. Thanks for explaining concepts in a fun and clear manner!

[javiermachin]

Great Video. I love how clearly Don explains things. We live in an amazing time. LOVE FERMILAB!!!

[RustyDockLight]

Dr Don, you are the best teacher and your most important quality is you love what you do! Watching is always a pleasure.

[JackVogel]

Thank you for the ongoing uploads.
Haven't looked on any physics videos in a while, but I feel a sense of pure joy, and relief from the crazy stuff going on in the world, as soon as I do 🙏

[mugwump]

I've always seen you so calm and collected. I really wasn't expecting these "danger" segments!

[jaydunstan]

Wonderful material...please, DO NOT STOP, we love the videos, they have been informing us for years. Thank you for all that you do!

[garyc]

This, along with and followed up by "The origins of mass" are a truly enlightening combo. Thank you for them.

[judewarner]

I started reading the New Scientist in the 1950s and have studied Chemistry, Metallurgy, Psychology and other science subjects at graduate level, dipping into every known science along the way, with many of the popular ''usual suspects'' in science paperbacks. I've seen all those equations (no particularly advanced maths) there and I was always a duffer at maths. For my secondary school Physics Final Exam (''A'' Level) I derived the Ideal Gas Equation... from memory of the steps rather than by mathematical genius.

I do not recall ever seeing ANYWHERE that Einstein's famous equation only applies to STATIC objects!!! That piece of information alone answers at least one of my fundamental questions about mass at luminal velocities... great stuff... thank you.

[NondescriptMammal]

Thanks for this very clear explanation, I like that you show the nuts and bolts of how things work at the subatomic level, without resorting to a lot of analogies, which usually just confuse me further.

[krisrhodes]

If mass is just moving energy, and photons are moving energy, why don't we just say photons have mass?

[ThomasJr]

Wow, amazingly well explained video. I just didn't think that the math was that complicated as warned haha.

[harryviking]

At least light pushes me out of bed in the morning....😆

[tksrqnp]

To the man who is 67 and thinks his time is almost up... I'm 87 and still enjoy this knowledge. These videos are fantastic.

[XB]

These Fermilab videos are fantadtic.
This guy explains things very well.
Great to watch.

[psikoexe]

THANK YOU SO MUCH, this was my question and I feel so good when someone reads the comments to give such beautiful videos. I thought my comment would at most be featured in viewers thoughts section but I got a video to my question... And of course now I understand it so much better than before thanks a lot.