Mirrors and virtual images

Mirrors and virtual images 0

When you take a course in something you find out new words and phrases about that topic. When I was taking geometric optics courses in school I learned how mirrors work,  how light rays reflect and the resulting image they create. Your standard flat mirror creates a virtual image of you or of what you see in the mirror, virtual image being the new phrase. Thinking about that bathroom mirror, when you look at it, your reflection looks like it forms behind the mirror somewhere….the virtual image. It’s funny to watch an animal see themselves in a mirror because they think it’s another animal farther away from them.

But I started wondering how can light come from us (reflect off of us) and be perfectly put back together to create that virtual image. This is where I pull out my simplified Feynman explanation (links to 1 video of his explanation below) and try to explain it, assuming I understand this quantum effect. First, the light (photons) from us hits the mirror….everywhere. When I say everywhere, I mean everywhere. The optics classes taught me to use just one line or ray to make the virtual image but that doesn’t explain the details.

Maybe this will help with all the rays going everywhere. Some of them that are at a certain angle of reflection end up canceling out. Destructive interference…which effectively means no light occurs. Let’s say the time it took for that ray that wasn’t really at the right angle to create the virtual image, it met up with another ray which was just so slightly at a different angle and thus the time was just so slightly different, they crashed into each other and poof! Nothing left (basically). But the majority of the reflecting rays being at the right (correct) angle, create the virtual image because they survived and didn’t cancel each other out. I hope this makes sense. Doesn’t change how a mirror works but may help understand what happens to all those rays that really are everywhere.

There’s more! Briefly, those photons don’t just bounce off a surface like a ball. They have to interact with the atom’s electrons. And metals are used in mirrors (like aluminum) because they have a lot of electrons (and that’s why there’s metal in our wires that conduct electricity). We still call it reflecting though. The photon gets released at the same wavelength that it came in. If it didn’t, our virtual image colors might be all messed up!

One more thing about mirrors. There are a few cities that have erected huge mirrors (heliostats) to bring sunlight into their towns. Northern cities lose a lot of sunlight in winter. Check out these stories of these cities use of these mirrors.

Rjukan, Oslo mirror

Rjukan, Oslo mirror


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Muons and why don’t we know about these guys?

Muons and why don’t we know about these guys? 2

I like particle physics (muons aren’t a tribe in the amazon). But it’s all from a distance…meaning, I’m really fascinated with how we discovered these particles and figured out if they are elementary but I’m no physicist. We all know about the two particles in the nucleus of an atom….the proton and neutron. Those aren’t elementary. They are made of quarks; up, down, charmed and others. But let’s just talk about muons and I’ll start by saying that maybe a hundred just went through your body since reading this.

We’ve known about muons for more than 70 years. Is it important to know about them? Maybe, I don’t recall hearing about them until I started reading astronomy texts. When we take classes in high school, someone (some committee) decides what we should learn and I guess they figured we need to know the “basics.” My son is learning the basics I think in 2nd grade. He brought home a bar chart that he completed. I think he could go to work and make at least minimum wage now. They seem to be learning more than we used to a long time ago. I wish they’d teach a kids physics course to him.

A muon is an elementary particle which means we don’t think it’s made of anything else. What’s interesting about muons is that we can use them to our benefit. And people are doing that now. As a matter of fact, 50 years ago someone used them to find out what was inside a pyramid. This is where this gets interesting. It’s all the sun’s fault. Particles like the muon are spraying down on us all the time and we know if they hit something in particular they might scatter slightly. Why not put a detector under the pyramid and see how those muons scatter. It was thought that this one pyramid in Egypt might have a special burial chamber. Instead of disturbing the Great Pyramid of Chefren they put detectors underneath it to find out how those muons behave after going through the pyramid.

Science is way ahead of most of us (it’s not too late to learn I tell myself). But, can you imagine how ingenius you’d be if you thought of applying something so simple as putting a detector underneath a pyramid? That guy, Luis Alvarez (Nobel Laureate), didn’t find a hidden chamber but he was seen as brilliant to come up with that idea (he was brilliant in plenty of other ways). So today we use muons in a similar way to detect what we can’t see. It’s one of the ways we search cargo for nuclear material. Muons behave a certain way when they go through high density materials. We can thank the Department of Homeland Security for applying this method to check for this stuff.

Here’s sort of a list of elementary particles, in case you wondered.

quarks, neutrinos, muons, electrons, photons, gluons, gravitons (hypothetical) and bosons (yeah, the Higgs is one of those guys).

Wow! So the protons and neutrons and electrons are all I learned in school but there are a huge number of other particles…that are known knowns…thanks for the phrase Donald R.

Here’s an interesting study using muon tomography (detection),


muon detector

muon detector


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