Relativity - Atomic Clocks

[ll_billym]

The basis of the GPS system is time, each satellite has atomic clocks onboard to maintain accurate time and frequency. Because the satellites are moving faster relative to the clocks in the GPS receivers on the earth, the time, and therefore the clocks on them run slower than on earth, by an easily measurable amount. The system has been designed to compensate for this.

My question is, and it doesn't just apply to the GPS system but more genarally about relativity I suppose, the atomic clocks work by measuring atomic radiation so what is it about moving at speed that slows down this radiation activity?

The simple answer I suppose is that 'time itself slows down' but (a) I don't understand how this works, and (b) maybe there is something about moving at faster speeds that makes physical processes just happen slower?

[R1Geezer]

yes time itself slows. atomic clocks merely count the oscillations of cesium atoms which are incredibly consistant. so the time dilation can be ascertained and is of course calculable by eqations supplied by a certain mister Einstein.

[ll_billym]

This is the bit that I need explained then. If the time dilation is inferred by the slowdown of the radtiation, how is it known that it isn't just the radiation slowing down?

I do have a fair laymans degree of knowledge in this area but I am just looking for a deeper understanding of the meaning of 'time slowing down'.

Actually I sell atomic clocks into the telecoms and research markets so I know a little about how they work, the atomic clocks currently being developed will be so accurate that their height above the earth (i.e. which floor of a building they are on) will need to be factored into their timekeeping measurements due to relativity effects caused by the earth's spin as the top of a building moves faster than the bottom.

[Vagrant]

I'm not sure it can be explained - it's counter intuitive, so difficult to understand, but nevertheless, it happens.
If you have a heartbeat of 60 per minute, and a grandfather clock with a 1 second pendulum, then your heart beats coincide with the clock's ticks.
This happens whether you are stationary, or moving close to the speed of light.
If there are two people and two clocks, one stays at home, the other gets into a spaceship and accelerates to near light speed, coasts for a while, and then returns, then more time will have elapsed for the moving person - exactly how much depends on how fast they went for and how long - but it could be, for example, 1 year and 50 years. It doesn't matter what you use to measure the time - pendulum ticks, heartbeats, atomic clock ...

[ll_billym]

Vagrant:- Heartbeats are not regular at all and I'm sure travelling at incredible speeds will affect the body and heartbeat rate. Pendulums will be affected by acceleration.

Why doesn't radiation get affected by high speeds also?

[beso]

Reality has four dimensions (three Spacial and one Time). Nothing is actually stationary and in fact there is only one speed. Everything in the Universe always travels at the speed of light. What we consider stationary is actually traveling in the direction of Time at the speed of light.

Any movement through space reduces the speed available to travel through Time so time has too slow down. The change can be calculated with a triangle using Pythagoras's Theorem. The hypotenuse is the speed of light. The other sides represent the speed through space and the speed through time.

At rest the speed through time is the speed of light. At low speeds the time axis changes very little. As speed through Space increases the effect becomes more and more pronounced until at the speed of light time stops entirely.

[beso]

We know that what happens is Time slowing because it is not the only effect. As speed increases so does the mass of the moving object.

This effect is inextricably bound by the Law of Conservation of Momentum. Momentum (velocity x mass) is the only attribute that is seen as the same regardless of the frame of reference while the perception of time, mass and velocity are all affected. Beacuse time slows down it also appears that the velocity of an approaching object is less. The mass increases to maintain the correct momentum.

This effect is best seen in the LHC. The protons (hydrogen nuclei) travelling in the circuit are the equivalent of the hydrogen under standard conditions contained in the volume of one small grain of sand.

At full power this tiny mass has the kinetic energy equivalent to the French TVG train travelling at over 220 km per hour. Much of this energy is embodied in the increased mass.

An object with any rest mass at all has infinite mass when moving at the speed of light. This increase in mass is the main reason that no object and reach the speed of light. Infinite energy would be required to fuel the infinite mass. Light can move at the speed of light because it has no rest mass.

[Vagrant]

You're missing the point by concentrating on irrelevant detail - yes, pendulums are affected by acceleration - but if the acceleration and deceleration times are short compared to the coasting time, the variation can be ignored.
Yes, heartbeats aren't as regular as a pendulum - but they are when averaged over a long time.
Travelling at immense speeds does absolutely nothing to a body - if you're asleep in a bed in a closed room and it's dark, you have no idea whether you're moving or stationary.
The important point is that while there is 1 second between heartbeats for the stationary person, there are (say) 50 or 500 seconds between heartbeats for the traveller - they each think their heart is beating once per second - but time is running at different rates because of their different speeds.

[jake-the-peg]

Just to make life more confusing you get time dilation effects not only through fast movement (special relativity ) but also through gravity (general relativity) and when you are measuring time this accurately the fact that a satellite is further away from the earth can require correction too.

Time runs faster for them due to this