Measuring distance with time

[HydrogenBond]

When we measure the vast distances of space there is no ruler or meter stick that allows direct measurements. Things are too far. We have to infer these distances indirectly, using time to measure distance. As a simple example, we could bounce a laser off the moon. We measure the time and knowing the speed of light, we then back calculate distance. When we think in terms of space we also think in terms of space-time. Even though space gets top billing it is a secondary calculation. In other words, when it comes to space we can know distance from time. We can also know time from distance, but only if we first use time to help us get handle on the distance. Shouldn't we call it time-space to be more in line with time's lead role in space calculations?

[Janus]

Distance measurement methods that do not rely on time:

 

Heliocentric Parallax

 

Spectroscopic Parallax

 

Dynamical Parallax

 

Type 1A supernovae visual magnitude.

[HydrogenBond]

With respect to the first three, a static system will tell us very little, until we add motion, period or time to get distance. Even the red shift was originally based on time. The original observations with Doppler shift may have been connected to the change of pitch of a passing train. The pitch is connected to a frequency change. Now doppler shift ignores the money variable.

[HydrogenBond]

The idea that time is the predominate variable can be demonstrated with a simple experimental observation. What we need is a meter stick and a stop watch so we can measure distance and time, independantly.

 

I don't know about you, but my meter stick doesn't need any type of power supply to measure distance. I have has it for years and have never changed the battery. On the other hand, to measure time one needs energy. It could be direct electrical power, battery, solar energy, a spring, pendulum, etc. Distance is a passive variable, which is why no power supply is required for a meter stick. But time is a dynamic variable, since one needs energy to measure time. Time has something extra, since it can not be measured passively, without energy. I am not talking about calculations but direct measurements.

[Shyam Bharath]

But i have this feeling that measurement with time may not be accurate given the fact that we all exist on a relative plane. Also when we look at a heavenly body, we are actually looking at its state some millions of years ago. By the time our light source / signals reaches that spot.... poof.... it would have vanished

 

Of course the same problem doesn't occur when measuring distance to the moon :)

[UncleAl]

A relativistic universe has four distinct distances: luminosity (inverse square), angular diameter, parallax, and proper motion. No two of them need agree to maintain consistency.

 

Clocks can only be synchronized by being local.