# Are photons/light a special property?

1. Feb 4, 2014

### batmanandjoker

Photons demonstrate superposition without having to be isolated from the enviorment. My question is does this only apply to light because I know you cant observe superposition in electrons unless theyre in a vaccum. This is my question in a nutshell. Are there any other propertys that demonstrate superposition without isolating it from the enviorment? Sorry for the spelling my spellcheck doesent work.

2. Feb 4, 2014

### Staff: Mentor

That's not quite right. Whatever you use to demonstrate superposition, it has to be isolated from anything in the environment that it might interact with. Electrons interact strongly with room temperature air; photons don't. That makes it a lot easier to set up experiments using photons, but there's no fundamental difference between the two.

3. Feb 4, 2014

### batmanandjoker

yes but "physical" matter is made of elctrons protons and nuetrons not photons. And nothing is faster than the speed of light/photons.

Has anyone tried the double slit experiment using electrons without putting them in a vaccum? I think so right?

Last edited: Feb 4, 2014
4. Feb 4, 2014

### Staff: Mentor

No, because if you don't have a vacuum the electrons won't even make it to the slits, let alone through the slits and to the screen. They'll be stopped by the air molecules - that's what "interact strongly" means.

5. Feb 4, 2014

### batmanandjoker

Do any particles or things exhibit superposition aside from photons without isolating it from the enviorment in some fashion?

6. Feb 4, 2014

### Staff: Mentor

There is no difference between photons and electrons as Nugatory already answered. If you want superposition then the particle needs to be isolated from anything that it might interact with in the environment. That applies to both photons and electrons.

Imagine that you tried to do the double slit experiment in mud instead of air. It would not work because photons interact strongly with mud. The only reason that it works in air is because photons do not interact with air very much (which is why air is transparent and mud is not).

The only difference is the class of things that each particle interacts with. Air is like mud to electrons.

7. Feb 4, 2014

### batmanandjoker

I guess a fear that I have which you might be able to put to rest is that the human body is constantly interacting with many diffrent things/particles and therefore doesent demonstrate superposition. Is this correct?

8. Feb 4, 2014

Don't Worry, Be Happy – YOU are NOT in a superposition, 100% guaranteed.

9. Feb 4, 2014

### batmanandjoker

how,why?

10. Feb 4, 2014

### StevieTNZ

That's making quite a statement. Do you have any references to back it up?

11. Feb 4, 2014

Have you seen any humans in superposition lately?

12. Feb 4, 2014

Because, for a composite object like the human body, to be in a superposition means that the whole collection of particles must be in one of two quantum states $|0\rangle$ and $|1\rangle$, and this only works if each configuration is equally likely, and this only works if the two states are equal in energy.

The average human body contains roughly 7×1027 atoms, i.e. 7 octillion atoms, i.e. 7 000 000 000 000 000 000 000 000 000 atoms.

How do you make sure that every one of these 7 octillion atoms is equal in energy, huh? Not an easy task, right?

The only feasible way to do this it to cool the composite object to its ground state (i.e. its lowest energy state). This is the only way to control 7×1027 atoms.

What temperature would that be?

Well, I don't have the correct answer, but a wild guess would be somewhere between 0.025 K and 0 K.

What is K? And why 0.025 K?

K stand for Kelvin and is a temperature scale, using absolute zero as its null point = -273.15 °C. The 0.025 K comes from a QM experiment where an acoustic resonator, consisting of about 10 trillion (1012) atoms, was cooled to its ground state. As you see, the human body has many orders of magnitude more atoms then the tiny resonator (60 µm), hence we will get much closer to 0 K than the other way (i.e. extremely hard to do in practice).

Therefore I can absolutely guarantee you that you will have a very distinct "feeling" in your body , loooong before even getting close to anything like a superposition. Trust me!

P.S: Superposition in the acoustic resonator lasted just a few nanoseconds (10-9) before being broken down, so any human going through this frozen hell gotta be ready for the action!!

13. Feb 4, 2014

### Staff: Mentor

Here's a purely classical example that you might want to consider.

There's a table in front of me. (I've propped my legs up on it and it's conveniently supporting a bottle of cold Mexican beer - this is all very comfortable).

There are air molecules bouncing off the table from below, exerting atmospheric pressure on the underside. There are also air molecules bouncing off the top of the table, exerting atmospheric pressure on the top side of the table. Pressure on top balances the pressure from below so there's no net force on the table and it stays put.

But suppose, just by random chance, it just so happened that every single molecule underneath the the table just happens to moving upwards at the same time? The table would blast upwards through the roof of my house like a rocket. This isn't impossible. All that needs to happen is for every one of about $10^24$ molecules, each of which has a 50-50 chance of moving up or down, all to be moving up at once.

The chances of that happening are $2^{-{10^{24}}}$. That's way more likely than the chances of every one of the $10^{28}$ or thereabouts atoms in your body all happening to end up in the the same superposition at the same time.

14. Feb 5, 2014

### batmanandjoker

so unless all the atoms in my body are in the same energy state which is highley unlikley I or any parts of my body will not exhibit superposition. Is this correct? But are some of the indivisual atoms or even cells inside my body in superposition?

Last edited: Feb 5, 2014
15. Feb 5, 2014

Nice explanation Nugatory! :thumbs:

16. Feb 5, 2014

Correct, all the atoms in your body must behave in a "synchronized" way (or the technical term, coherent) to exhibit any type of quantum properties. This could happen spontaneously by an extremely tiny chance, or we could assist by cooling the body to its ground state (not recommended). Anyway, it would only last for a tiny fraction of a second, before it breaks down.

You could also think of it like this; most of matter is actually empty space, including your body, in the atom we have the compact nucleus, but the distance to the electron(s) is quite large (on this scale), and you have even more distance to the next atom, hence the largest "volume" of your body is just empty space. Therefore – strictly theoretical – you should be able to run through walls!

However, you probably have much greater chances to win The Mega Millions Jackpot 10,000 times in a row, than every atom of your body gets positioned in exactly the right location, in relation to the atoms in the wall, for you to pass right through it.

Brigadier General Hopgood learned this the hard way...

Disclaimer: DON'T TRY THIS AT HOME!

The body is a hot place, not especially suited for quantum states. It could probably happen spontaneously, but decoherence timescale would most likely be extremely rapid. But I'm not sure about this...

Anyhow, it's absolutely nothing to be 'scared' of, because you will never notice any difference whatsoever, promise.

17. Feb 5, 2014

### Staff: Mentor

Cells or even atoms? No. (OK, you can say "maybe" if you want, but as with my flying table we're talking "maybe" so small that it is might as well be "never").

Individual electrons? Sure, happens all the time, it's part of how chemical bonds are formed.

18. Feb 5, 2014

### batmanandjoker

your talking about electrons that have decoupled from atoms, correct?

19. Feb 5, 2014

### sophiecentaur

There are many instances (although, possibly a minority) where EM waves do not superpose. Wherever the medium is non linear then |E1 + E2| ≠ |E1| + |E2|. I don't know what you mean, precisely, when you talk of Photons 'superpose'. It would not be hard to envisage two photons, of the same energy, having twice the energy of one of them so you could say that superposition applies there. But, once those photons have interacted with a medium of some kind, the energy could be redistributed in some way. What is your understanding of the term? It is used in several different contexts.

There are some very significant differences between bosons, such as photons, and fermions, most of the other better known particles. That definitely affects the way the two types interact with matter. Could this be what you are getting at?

20. Feb 5, 2014

### batmanandjoker

So the majority of the indivisual atoms energys in our bodies are flucuating constantly with diffrent energy levels.Is this correct?