Curious Particle Experiment?

Question

I remember watching a BBC programme showing experiments which suggested the existence of unseen matter .

They sent a single stream of protons(??) at a detector plate and you could see each individual strike.

The strange bit was they then put between the emitter and detector a card with a slit which as far as I can remember should have resulted in a predictable change to the particles received. However the results were - strange. It seems there were 'ghost' particles with no explanation of their source - other than it was hypothesised they could be coming from another dimension possibly??

Any suggestions greatly appreciated

Answer 1

Quantum physics has proved that particles such as protons also have wave-like behavior.   Inversely similar to a photon.  We know light is a wave, but we can break it down into individual packets.

There is something called the Heizenberg's Uncertainty Principle which briefly states you cannot measure a particle's speed and location at the same time.

So the experiment you are talking about relates to that.  The protons act as a wave and will scatter through slits like a wave rather than an invidual particle (which has one landing spot).  The whole experiment collapses when scientists try to measure the wave.

Answer 2

Yeah i saw that documentary too.

But surely trying to measure something so small, you are going to influence the result.

Answer 3

The Copenhagen Interpretation of quantum mechanics suggests that an observer must interact with a quantum system to make an observation or obtain a measurement. This interpretation provides a starting point for an explanation to your question.

When a beam of protons strikes a detector then the experimenter may measure each proton's arrival as he/she interacts with the quantum system and 'collapses the wave function' in making the detection.

The protons are half integer spin particles known as fermions and their quantum state may be mathematically described by a solution to Schrodinger's wave equation. This solution is known as the wave function and it contains all the information about the protons that it is possible to know. However, the Heisenberg uncertainty principle does not allow the observer to measure exactly both the momentum and the position of the protons. The two variables are said to be mutually exclusive so that the more accurately you know one the less accurately you can know the other.

Thus, in the first part of the experiment the observer was ‘collapsing the wave function’ and observing the proton's position without knowing anything about their momentum.

When the slit was placed between the proton source and the detector, the experiment became a diffraction experiment. As the protons left the slit, their wave function’s interfered with each other and the pattern observed on the detector screen was that of an interference pattern. The 'ghost particles' where a consequence of constructive and destructive interference between elements of the proton's wave functions. The detector screen is not measuring the exact position of the protons. Thus, Heisenberg’s uncertainty principle is obeyed when the observer ‘collapses the wave function’ and looks at the screen. If, however, the observer measures the path of every proton to the screen then he or she will have measured the exact position and so the diffraction pattern will disappear.

The two experiments demonstrate that particles have both a wave and 'particle' nature and it depends upon the experiment as to which model applies.  Finally, Microsoft’s ENCARTA encyclopaedia comments, ‘The French physicist Louis Victor de Broglie suggested in 1924 that because electromagnetic waves show particle characteristics, particles should, in some cases, also exhibit wave properties. This prediction was verified experimentally within a few years by the American physicists Clinton Joseph Davisson and Lester Halbert Germer and the British physicist George Paget Thomson. They showed that a beam of electrons scattered by a crystal produces a diffraction pattern characteristic of a wave. The wave concept of a particle led the Austrian physicist Erwin Schrödinger to develop a so-called wave equation to describe the wave properties of a particle and, more specifically, the wave behaviour of the electron in the hydrogen atom.’

Answer 4

was it like this?

http://www.youtube.com/watch?v=6Q4_nl0IC...

it explains itself...

Answer 5

All matter is unseen. The particles to which you refer were analysed and identified as Pz cosine gamma %8 "&^* and a bit. Possibly a byte. They emanated from the 6th dimension and seem to have broken Eistein's rule of thumb.

The follow-on programme told us not to worry about it.

Answer 6

I believe that you saw a program on the wave-particle "duality" of the photon.  Just as Certs is a breath mint AND a candy mint, so too, a photon exhibits characteristics of both a wave and a particle.  If you put the photons through a double slit, you will get a "diffraction" patterns on a screen in front of the slits.  The pattern will be vertical areas of bright and dark (width determined by the number of slits used)...Google "Young's Double Slit Experiment" for more.  The issue is this...if you measure which slit the photon goes through, the nice diffraction pattern disappears.  Only when you "discount" the particle nature, do you "see" the wave nature.  This is certainly an odd non-classical physics result.

A few comments on other answers that have a few things wrong...

There is no need for extra dimensions to explain what is going on.  In my opinion, the "best" treatment of this for the "novice" (but talented) physics student is in Richard Feynman's three volume lecture series from Cal Tech.

This is not what Einstein called "spooky".  That was his description of entangled particles that were separated by great distances.  Influencing one "changed" the other even though that interaction would be "faster than light" in some sense.

This "collapsing" of a particles "state" is a result of the Copenhagen convention...a purely arbitrary agreement between some of the brightest founders and dabblers of quantum.  There are other ways to deal with multiple superimposed states.  I recommend "Scientific American" and their supplement of 2007, I think, dealing with quantum "oddities".

You have found one of the great demonstrations of the "failure" of classical physics to explain the Universe.  I know that my introductory answer is a bit "rough", but I hope it acts as a point of departure in your quest for knowledge.

-Fred