An alternative definition of time
9 Nov 2011, 5:07AM
So now we need to consider an alternative definition of time. One that is independent of speed or temperature.
The first thing to note is that we cannot keep time by via the interactions of particles, as if these particles are bouncing around, moving relative to each other or moving at all, then their movement will be effected by speed in a given direction (as per relativity and our previous discussions). This rules out a lot, all mechanical or digital clocks, in fact anything constructed from matter.
What does it leave us with? A clock constructed from light? Einstein used a "light clock" in his thought experiments, consisting of light bouncing between two mirrors and showed that it would slow down if travelling close to the speed of light.
So what else do we have? First we don't know what speed the Earth is travelling (in the universe), nor what direction. We must assume it is something non zero as we know it is moving around the sun and the solar system is moving around the center of the milky way.
So can we construct a clock from anything that is limited by the speed of light (light included)? First thought would say no, as everything will be effected by movement. Second thoughts (what I call random brainstorming by the subconscious) brings up a few ideas.
1) Can we use the frequency or wavelength of light? We have light of many different frequencies, these can be shifted by speed (think red/blue shift of galaxies approaching or receding from us). So once again we have to ignore all light from all moving matter. Effectively all stars in the nights sky.
2) That leaves the cosmic microwave background radiation (CMBR). This is supposedly left over radiation from when the universe went transparent to light. Since that time (~380,000 years after the big bang) that light has been travelling out to finally reach us. The CMBR is everywhere in the nights sky, pretty much uniform at 2.725K temperature and peaking in the microwave spectrum. There are small fluctuations within it. The question is since this light has been travelling directly towards us since "soon" after the big bang, can we use it to keep track of time?
3) The width of universe may be a good measure of time. However its impossible to "see" this from within the universe as it has taken light the age of the universe to travel half this distance.
#2 has some potential. If we know the initial temperature of the CMBR from when the universe went transparent and the temperature now is known (2.725K) then we can interpolate from then to now to get the absolute time since the big bang. This may now work for a number of reasons. On a day to day basis the temperature change may be too small to be measurable making any kind of time keeping on a day to day basis untenable (e.g. can we determine a measurable difference in temperature over 1 second? Probably not!). We're also assuming that the expansion of the universe (what exactly is meant by this huh) is uniform over time, what we really mean is that the temperature drop is a linear relationship whereas its possible it was not in which case we cannot interpolate. Finally is the universe spinning? And would this effect the CMBR radiating out (e.g. some of its speed goes in the direction of spin)?
So in summary we would probably say that there is some theoretical absolute time that some observer outside of the universe could keep but from within the universe I can see no way to keep track of time without the difficulties we encounter with relativity.