Here I aim to lay down 10 of the key theories and notion in Physics - chosen simply by the ones I believe are the most interesting and important. They are in no particular order and there are many theories I could well have included but to prevent this article stretching on too long, i have chosen to stick to 10.
1) Newton’s Law of Gravitation
One of the most powerful ideas in Physics, Newton’s revelation of ‘gravity’ still stands centuries after it was formed (be it slightly modified by Einstein’s theory of General Relativitiy). The notion supposedly came to him after seeing an apple fall from a tree, whether this is true or not we will never know but he came to the conclusion that all objects are attracted to each other through gravity which is affected by mass.
The strength of the force is affected by the mass of the objects involved, and both objects are attracted to each other – the apple is pulled towards the Earth but at the same time the Earth is pulled towards the apple. It is only because the Earth’s mass is so much greater that we do not notice the latter.
His ‘Inverse square law’ explains how the strength of the gravity decreases by the square of the distance from the object. So if you were twice the distance from the Earth, gravity would be 4x weaker.
His theory suddenly explained the motion of the planets and tides.
2) The Big Bang Theory
Unlike some of the others, it is quite probable you know a fair bit about the big bang theory already - the idea that the universe was created in a colossal explosion creating all space, matter and time. The corresponding ‘Big crunch’ theory is less well known – the idea that the universe will eventually collapse in on itself to form a massive black hole and perhaps restart again.
One key observation led to the formation of the big bang theory. Edwin Hubble noticed in the 1920’s that all galaxies he could observe appeared to be moving away from us – he could tell this because they were ‘red-shifted’ or the light from them was travelling slower making it appear red. From this it seemed rational to conclude that the universe was expanding and if you know the universe is expanding it seems probable that it originated from one point – the Big Bang.
To give you some idea of what kind of ‘explosion’ the big bang was, 10 picoseconds after the explosion – about as close as we can predict conditions without breaking all know physics principles, temperatures were around 1-2 quadrillion Kelvin. All matter was compressed into on infinitely dense point and expanded faster than the speed of light.
From this physicists can see 3 alternate scenarios for the universe. Eventually the expansion of the universe is slowed by the universes own gravity until it collapse in on it self – a closed universe. Secondly, gravity proves to be too weak and the universe continues to expand forever until it becomes cold and all stars die – an open universe. And lastly gravity is exactly right and balances in a non-changing universe. This is all confused even further when we note that the universe is actually expanding at an ever faster rate meaning some other force must be acting upon it which we yet to understand.
3) Dark Matter
Scientists have calculated that there is a vast discrepancy between between the amount of mass in existance in the universe and the amount of gravity that must be holding the universe together. From this it is believed that the visible matter in the universe accounts for less than 10% of the universes mass and the remaining 90% is made up by 'Dark Matter' - a mysterious hypothetical material that can not be observed as normal matter can.
There is very little evidence for 'Dark matter' but it has been observed through the effect it has on distorting light from distant stars over vast distances. There is much dispute over what dark matter really is.
4) Relativity
Einstein's General Theory of Relativity preposed that gravity causes space to curve around it, distorting the space around a mass and warping it, much like an object on a bed sheet would distort and bend the sheet around it.
Some of the things this explains and descibes include:
- The fact that time is slower in higher gravities.
- Light can bend due to gravity, despite having no mass.
- How an object drags the space time around it along.
This has some fairly remarkable ideas, for example, it states that if you were to leave the solar system in a space craft traveling close to the speed of light, time would pass so much slower for you that you would in fact arrive back at earth, having aged only 50 years or so, to find billions of years had passed. This is experienced all the time in every day life but is not noticeable, for example, you step off an aircraft after a long flight up to a second younger than if you had never flown.
credit to hellodave.hubpages.com
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