Quantum Tunneling

[MaxTheLimit]

In this debate I would like to discuss the validity of Quantum tunneling as discussed in THIS (http://www.dailytech.com/German+Scientists+Declare+Speed+of+Light+Broken/article8487.htm) article. It states that the speed of light can be broken by this method. If this were true it would greatly alter our understanding of universal physics. Let's discuss and debate.

[Can Not]

Basically they did something few people could comprehend and now you want to argue over speculations based off the experiment?

[Mad Scientist]

That article is most poorly written indeed.

Quantum tunnelling is NOT a violation of special relativity. I understand how people may think it is, but this is a misunderstanding. I think its time for a

MAD SCIENTIST SCIENCE LESSON

Quantum tunnelling is quite difficult to explain, but i will do my best. Firstly we must remember that particles cannot be pinned down to an exact location according to quantum mechanics. The reason why is the Heisenberg uncertainty principle, and is explained here (http://forums.gamernode.com/showpost.php?p=217949&postcount=28).

All we can do is give a rough idea of the region of space as to where a particle is. For example, lets think of something called a "particle in a box" thought experiment. Most people know that objects with a like charge repel. Suppose we had an electron (which has a negative charge), and we place it between two plates which also had a negative charge like so:

http://img443.imageshack.us/img443/1413/qt1dc0.jpg

The electron cannot move left or right, because if it moves closer to the plates it gets pushed back towards the middle. Depending upon how fast it is moving it may get very close, and it may even penetrate a small way through the plates, but it will still get pushed back to the middle.

Unfortunately, drawing the electron as a little dot doesn't work. Particles cannot be thought of as a point, they are a fuzzy cloud of probabilities of where we think the electron really is. So we have to draw a graph of the "probability amplitude" of the electrons position. This is basically a graph of how likely we think it is to find the electron at a certain point. It would look a little like this:

http://img530.imageshack.us/img530/1637/qt2df9.jpg

The part where the graph is the highest (the middle) is the part of the apparatus that we would be most likely to find an electron. The red regions represent the plates, this is why the graph is very low around and in the plates, because we would not expect it to be very likely to find it in the plates at all. Now, if the particle gets faster, the graph flattens out a little. Because the electron moves faster, it would be able to get closer to the plates, making it slightly more likely that it is found nearer the plates. As a result, we get something like this -

http://img155.imageshack.us/img155/8403/qt3gx2.jpg

Note that a small proportion of the graph lies outside the metal plates (shaded blue). This represents the very small, but still real chance that we may find the electron outside the plates. In other words, the electron has somehow managed to teleport or "tunnel" outside the box.

This explanation is a bit of a simplification, but it explains the principle as well as i can without mentioning De-Broglie wavelengths, or having to solve the one dimensional, time independent, Schroedinger-equation for a particle in a box.

Contrary to what that article says, the phenomena is well understood. Indeed, the semiconductor diodes in your laptop rely on this phenomena to allow electrons to tunnel through the silicon junction that comprises a basic diode (for this reason, they are sometimes known as "tunnelling diodes"). The fact that the composition of the different types of silicon has to be precisely adjusted or the electrons will tunnel at the wrong voltage tends to suggest that scientists and electrical engineers are fairly confident that their explanations of quantum tunnelling are as accurate as we can currently do.

So does this violate special relativity? No.

The reason why is that special relativity states that it is impossible to accelerate particles beyond the speed of light. If you can get them to travel faster than light without acceleration (indeed, by instantaneous teleportation), then relativity is not violated. I am confidant that this paper by these German scientists is little more than media sensationalising, and will be torn apart by peer review. QED.

[morolen]

also, if i remember correctly isnt electron spin something like 2c?

[Mad Scientist]

Well spin is a measurement of angular momentum (units of newton.meter.seconds), rather than velocity (meters/second). If i remember my fundamental properties correctly, then i believe it to be 1/2. However i could be wrong on that particular one. although it is considered wrong to think of it as the particle spinning like a top. sort of.

however electrons do posses a quantity called "g-factor" which is closely related to spin, and very close to being 2. It may have been that that you are thinking of.

[Psyborg]

Mad Scientist always comes through to explain this stuff in layman's. Thanks, sci!

[morolen]

yea from what little i know(read very little) quantum tunneling is necessary for the sun to burn. Its necessary for the particles to overcome the coulomb barrier, or did i make that up madsci?

[MaxTheLimit]

Basically they did something few people could comprehend and now you want to argue over speculations based off the experiment?

Shut up then GTFO. The content of this debate was clear, and no one needs you restating it. You you don't have content to add then you aren't welcome.


Near the end of the link it mentions that everything proceeding that point is invalid thus totally negating anything the article is about. It's shrewd writing tool to only put that snippet of info to not make it obvious the article is a waste of time. As ridiculous as it would seem, what thoughts do the viewers of this forum conceive if we manage do develop some way to force particles beyond the theoretical barrier, the ramifications to the real/scientific world. I keep my reserved judgments and opinions until later...Have at it!

[TheTaxidermist]

Damnit, 3:30 is not the time for science lessons. sonuva.

[jambo]

Thanks for that Mad Sci, helped me a heap to understand it =]

[Viktor Berg]

Teleportation! I love teleportation!

Mad Sci, if I remember correctly, you may or may have not before created a post about quantum teleportation. Could you please provide me with the link of it?

[Kaze]

Anything with the word quantum is inevitably cool.

[Atomic Waffle]

Quite.

[MaxTheLimit]

Quantum... necrophilia?
Quantum... sodomy?

...now that you mention it it does make it sound like something sci-fi no matter what it proceeds.

So if you look at it logically:
Quantum = cool
therefore quantum tunneling = cool
cool > common sense
so
quantum tunneling must be real because it's cool. We all no being cool is far superior to being rational.

[Jabode]

So what is the difference between teleporting and accelerating? To change position without change in velocity means there was no acceleration?

Isn't velocity defined as the rate of change in position? So by changing position instantly, doesn't it mean the the velocity is un measurable and, one would assume, faster the light?

Please tell me where my logic is wrong, or how this is explained.

[Kester]

Technically, you are correct.

[Jabode]

And what about when its applied? :)

[Viktor Berg]

It cannot be applied. Due to the fact you can never provide unlimited energy to an object. Since E=(mv^2)/2, where E is energy applied to an object, m is its weight, and v is the speed. However, at speeds close to the speed of light, the formulae changes (Newtonic physics fail epically at this point :haha:):

E=(mc^2)/√(1-(v/c)^2) (correct me if I am wrong)

where v is the speed of the object, and c is the speed of light. There are 2 things to notice in this formulae:

1. The energy application is increased dramatically even at sub-relativistic speed. (mv^2)/2 is replaced with mc^2

2. The part after the "/" sign worsens things even more. Generally, this part means following:

when v is relatively low, the (v/c)^2 part stays close to the zero, and the whole thins is close to 1. However, as v approaches c, following stuff happens:

lim(v->c)(<=this syntax generally means "limit", as in "approaches") = √(1-(c/c)^2) = √(1-1^2) = √(1-1) = √(0) = 0.

Now, look at what we get:

E=(mc^2)/0. We all know (or should know) that you can't divide with zero. But we can divide with a number that is INCREDIBLY close to 0, but is not 0. Let's say, divide with 0,0000001. It generally means multiplying with 10,000,000. Scared yet? And we haven't even approached speed of light!

Also, you can't go beyond the speed of light (aside from quantum teleportation, I think) because in that case, the sqroot would have been taken from a negative number, which is impossible (does not produce a rational number).

(Mad Sci, feel free to correct me on this post, my level of knowledge of relativity is limited by my high school education and some additionally read articles).