Why Do We Express Communication Signals As Variable Of Time

Because that's how they vary and that's how we perceive/receive them.
Could try plotting them against the local price of vegetable... but that would be fruitless.
If a signal does not vary with time, is it still a signal?
Discus.
Del

Same problem, my local vegetable prices don't vary much

You could express a communication signal as it varies in a spatial coordinate system if one knows the propagation velocity of the media. Most of the time though this would be a useless measurement system for communication signals but one could most certainly do this.

One of the complications of trying to reference a communication signal to a spatial coordinate system is choosing a single spatial coordinate reference system. Do we choose a transmitter outside of Bhopal, the geographic center of the earth, the center of the solar system or the Milky Way galactic center as our spatial reference zero. Each of these inertial reference positions will certainly be valid reference points that can make certain problems and phenomena easier to understand. However, an engineer designing the feed horn or Yagi element lengths of an antenna for a radio astronomer will not care how the spatial coordinates of the antenna will change as the Earth moves around its axis. Since time does not change for the radio astronomer or the antenna designer, referencing signals to time gives a common usable standard so that a project can be built.

Trying to be serious for a moment, any transmitted signal does have vectors that can be expressed in more dimensions than time - but then that is correct for the smart*ss answers, too.

Without modulating the signal I'm not sure you have communicated and demodulating it means against time.

I'd like to apologise for my comical associates. A little vegetable humor on a Sunday morning in the fall is always fun.

However, such a system already exists.

Here is a graphical representation. While part of the system operates at the speed of light, the indicator response is somewhat slower.

Flag positions in Semaphore

One way to visualize the semaphore alphabet is in terms of circles:

• first circle: A, B, C, D, E, F, G;
• second circle: H, I, K, L, M, N (omitting J);
• third circle: O, P, Q, R, S;
• fourth circle: T, U, Y and 'annul';
• fifth circle: 'numeric', J (or 'alphabetic'), V;
• sixth circle: W, X;
• seventh circle: Z

At risk of being pedantic, without time as a variable any given flag then becomes a single letter endlessly.

OK, maybe slow is an exaggeration.

I don't have time to explain further. I have to get back to the task at hand. I'm drying some paint.

GA...succinctly put

Could you perhaps give an example in which kilobytes per inch would be meaningful?

(Maybe for amount of information stored on a length of tape, but that doesn't pertain much to signal propagation.)

They can also be expressed as a variable of frequency. The instrument that displays this is called a frequency analyser.

Isn't frequency just the inverse of time?

Since time is the only non-tamperable, constantly forward-moving variable, it is logical to use it as a base for most things in life....even the very success and failure of human endeavour is time based (begging your pardon if it offends your sensibilities, young lady )

1. _{At age 4, success is...not peeing in your pants.}
2. _{At age 12, success is...having friends.}
3. _{At age 16, success is...having a driver's license.}
4. _{At age 20, success is...having sex.}
5. _{At age 35, success is...having money.}
6. _{At age 50, success is...having money.}
7. _{At age 60, success is...having sex.}
8. _{At age 70, success is...having a driver's license.}
9. _{At age 75, success is...having friends.}
10. _{At age 90, success is...not peeing in your pants.}