Updated: March 30, 2007
Absolute zero: definition - On paper, Absolute Zero is the temperature at which all molecular activity ceases. But what really happens? First, a bit of introduction is needed. Basically, there are two types of particles in the world: bosons and fermions. The first type are called after an Indian physicist Bose. These particles are characterized by whole-integer spin values and symmetric wave functions. A typical example are photons. The second type are called after an Italian physicist called Fermi. These have anti-symmetric wave functions and half-integer spin values. Protons or electrons belong to this family.
What does this mean? Well, in simple terms, no two fermions of the same kind can abide one another and will have to occupy different quantum states. In a way, it's similar to the repulsion between even polarities of a magnet; you can keep them together only if they are odd. This principle is called the Pauli Exclusion Principle and it's one of reason why attempts of going through solid matter usually results in a serious injury on behalf of the brave volunteers.
Bosons are much friendlier. You can have as many bosons piled up together as you like. If our bodies were made of bosons, we would be much shorter. Just a few nanometers, actually, if not less. Our particles would have no reason to repel one another and would bunch up into tight happy clusters. This partially explains why light - or any electromagnetic, bosonic radiation - is not palpable.
Technically, bosons are so friendly, they would all gladly bunch into a single large particle if not for some annoying Quantum Mechanics rules. The thing is, no particle is definite. Even photons are only defined to within a certain size. The two basic characteristics of any particle, its position and its momentum (read potential and kinetic energy) cannot be accurately measured. Such a measurement will always have a minimal standard deviation.
Let's call it:
In other words, each particle is a little box, with a fixed, constant volume:
If you measure the particle's velocity very accurately, you will smear its position and vice versa. Things are a bit more complex, since both momentum and positions are 3D vectors and the actual 'shape' of the system is a hybrid 6D entity, but that's not important now. Although, when you think about it, in a 6D world, the commutation relation would probably be:
To be able to make a completely accurate measurement, infinite time is needed. This Uncertainty Principle also prevents us from predicting the future of a particle - something that is rather quite trivial in Classical Mechanics. To fully understand the mathematical mechanism behind the model, one should have an inkling of familiarity with the Fourier transform and how it works.
Where does this leave us?
This leaves us with a very strict set of rules that still apply even when the temperature drops toward the absolute zero. But now, we know what to expect. Now, the question is: how do we achieve the absolute zero temperature? We're back to question one. Absolute zero can have several interpretations.
It is the temperature at which thermodynamics gives up. At absolute zero, you can have 100% efficiency. At absolute zero, there is no molecular motion and no heat exchange between processes.
Absolute zero temperature is also the state in which the system has the minimal quantum-permissible energy. For bosons, this is a quasi-2D soup (position-momentum) that approaches 1D limit (position only) by minimizing its kinetic dimension. Theoretically, the bosons all become an infinite smear in time. In a three-dimensional world, this means that the entire matter is concentrated on the surface of the time sphere. In such a world, history loses its meaning. The gentle time-space relation becomes irrelevant, because the curvature of space equals that of time.
Luckily, our world also contains fermions, which prevent this from occurring. In this world, fermions will bunch up as tightly together as possible within their intrinsic quantum limitations. Entropy would skyrocket toward +, but may or may not reach an upper value.
Fermions will add depth to the boson soup, leaving a minimal thickness to the space and forcing the physical rules to continue existing. For all practical purposes, we would not be able to distinguish the changes if they occurred.
|World at the absolute zero temperature is not very interesting: there's no light as photons refuse to move and assume a surreal state of being almost everywhere, playing Trick or Treat with Uncertainty and Time; fermions sizzle all around this bleak singularity, in a state of perfect vacuum|
In a way, We can see that our Universe obeys this law. Energy drops, entropy grows, temperature drops. The Universe is trying to cool down. In fact, it's not very far from reaching that goal. If not for the gravity, all matter would have dispersed around long time ago. The gravity keeps things glued together. Sometimes it's so strong it even defeats the Quantum Mechanics - enter the Black Holes.
But it all figures nicely. Supposedly, gravitation is inspired by particles with whole-integer spin of +2 called gravitons. In accordance with their nature, gravitons want to bunch up together. A battle between bosons and fermions, a war energy and entropy - keep our world alive.
Dark matter that everyone talks about - it could be part of an older, already cool soup of bosons. At absolute zero temperature, there's no more need for photons. And if the dark matter no longer obey the rules of the time-space thingie, it might nonchalantly ignore the rules of physics that force the hand of the rest of the Universe. So 'dark' matter really adds up well - fresh matter is converted as it reaches the absolute zero and time-space relations break.
To add spice to our story, we must ask: Will Universe cool down completely? That's a question no one can answer. But let's assume it will. Let's assume an Open Universe. The space will get thinner and thinner until it becomes a plate of matter with no bosonic radiation in it. A dark world indeed. Fermions will scatter around it, forming a zero-point energy cocoon. This new world will be almost two-dimensional. Fermions will keep the pressure and contain the bosons from stretching infinitely. Time also plays the part, defining the horizon to the events.
Some of the fermions might decay and vanish. All baryons (particles made of quarks - like protons) should have a half-life and eventually disintegrate into its basic ingredients. Leptons (elementary particles like electrons) should remain forever. Regardless, all being fermions, they will still obey my crazy model. One moment in time, this formation might collapse. The way I see it, two things could happen:
|Big Bang will most likely not be pink or purple, but it could definitely have a fractal nature|
Bosons and fermions exchange spin numbers, a sudden reversal that is reached as the soup's thickness shrinks below the Planck length and forfeits the rules of Physics. Suddenly the zero-thickness soup goes from minimum energy to maximum energy and bursts in a bright shower, scattering the bosons everywhere. Confused particles slowly react, forming up as they are scattered all over the place. Enter the Big Bang.
Bosons, kept under pressure by fermions, would like to escape. They do not wish to be contained. This causes a temporal pressure that distorts the symmetry of the formation. Eventually, the anomaly causes a rupture in the fermionic cocoon. The bosons escape. But they cannot stretch indefinitely. They are bounded by time. In panic, they spread around the circumference of the time sphere, trapping the fermions. Entropy goes from + to -. Time changes direction. Boom. Enter the Big Bang.
So ... an Open Universe becomes a Cyclic Universe. History repeats itself. Either time resets itself or the space resets itself. All in all, absolute zero temperature is not very interesting. It happens all the time. Every quantum system in the ground states is at local absolute zero. On the whole, things are much more complex. But eventually, it comes down to one thing:
A hot dog, with a fermionic bun and a very, very thin bosonic sausage. Sounds like a delicatessen. Especially considering it could be the reason why we're here. If you are interested in reading more about preposterous theories regarding these gentle topics, you might want to try: http://en.wikipedia.org/wiki/Absolute_zero.