Force-carrying particle - Sample Essay
A stationary object in a pool of water will not make waves. But an object spinning and splashing will create waves rippling away from it. Someone who observes them reaching the other end of the pool could deduce that a disturbance had occurred in the water, and might even be able to tell what produced the waves. In much the same way, the movement of massive bodies in the cosmos is thought to generate ripples in the fabric of space-time, which are called gravitational waves.
Detecting those waves will enable physicists to infer information about the phenomena that caused them. Pairs of incredibly dense neutron stars (with a mass 2 or 3 times that of the sun compressed into a 10km diameter) swinging around each other 100 or even 1000 times a second “churn up” space-time. This is also the case with stars swirling down into black holes and the formation or collision of black holes. They are all thought to generate gravitational waves, propagating outward across space-time at the speed of light.
As of yet no gravitational waves have been detected as the focus has been upon making the machine sufficiently sensitive. The Big Bang should have produced the hugest of all gravitational waves, and with the right instrument, physicists ought to be able to detect them. In order to predict the future position and velocity of a particle, its present position and velocity must be measured accurately. The obvious way to do this is to shine light on the particle – some of the light waves being scattered by the particle which can be detected by the observer -indicating its position.
However, light has limited sensitivity depending upon its wavelength – the accuracy with which the position of a particle can be measured is determined by the distance between wave crests. Thus, for precise measurements it is necessary to use high frequency (short wavelength) light. According to Planck’s theories, the smallest “unit” of light is one quantum – whose energy is higher at higher frequencies. But even one quantum of light will disturb the particle – changing its velocity unpredictably.
And the more energetic the quantum – the greater this effect will be. The more accurately you try to measure the position of a particle, the less accurately you can measure its velocity – and vice versa. Heisenberg showed that this value of uncertainty (the product of position uncertainty and velocity uncertainty) can never fall below a certain fixed quantity – Planck’s constant. 9 This firmly puts an end to the classical clockwork nature of the universe – prediction is impossible if the present cannot even be accurately mapped.
It is clear to see how “wave-particle duality” exists, as particles do not have a definite position but are “smeared out” with a certain probability distribution. And light can only be emitted or absorbed in packets, or quanta. 9 A successful unified theory must incorporate this uncertainty principal – Einstein’s theory general relativity leaves no room for quantum mechanics, Einstein famously stating himself that “God does not play dice”. In quantum mechanics, the forces or interactions between matter are all supposed to be carried by particles.
A matter particle, such as an electron or quark, emits a force carrying particle. The recoil from this emission changes the velocity of the matter particle, for the same reason that a soldier feels the recoil of the gun when it is fired – every force has an equal and opposite reaction force – Newton’s third law of motion. The force carrying particle then collides with another matter particle and is absorbed, changing the momentum of that particle. The net result of this process of emission and absorption is the same as if there had been a force between the two particles of matter.
Each force is transmitted by its own force-carrying particle – or gauge boson. A gauge boson with a high mass is indicative of a short range force as it would be difficult to produce and exchange them over a large distance and vice versa. 9 The fundamental particles fall into two “families” – leptons and quarks, each with three “generations” of successively heavier members. Spin is the intrinsic angular momentum of particles, given in units of h, which is the quantum unit of angular momentum where h=h/2? = 6. 58×10-25 GeV = 1. 05×10-34 Js. Electric charges are given in units of the proton’s charge.
In SI units the electric charge of the proton is 1. 6×10-19 coulombs. The energy unit is the electronvolt (eV) which is the energy gained by one electron crossing a potential difference of one volt. Masses are given in GeV/c2 (a rearrangement of E=mc2), where 1 GeV = 1. 60×10-10 joules. The mass of the proton is 0. 938GeV/c2 = 1. 67×10-27 kg. The Standard Model incorporates the quarks and leptons as well as their interactions through the strong, weak and electromagnetic forces. Gravity alone remains outside this model. Each force is associated with a gauge boson.
Photons carry the electromagnetic force, gluons carry the strong force, and charged Wi?? and neutral Z0 particles carry the weak force. The fundamental forces appear to behave very differently in ordinary matter but the Standard Model indicates that they are very similar in a high enough energy environment. The consistent way to treat the weak force is to unite it with the electromagnetic force – forming the electroweak force. This discovery is akin to the bringing together of electricity and magnetism as electromagnetism by James Clark Maxwell in the mid 19th century.