Maybe not a typical riddle, but here it is:
I can travel from there to here by disappearing, but I can also travel from here to there by appearing.
What am I?
I think the answer is
The letter 't'
The words here and there differ by the letter 't' which either appears or disappears depending on which direction you go.
What is that which can travel from there to here by disappearing
From our point of view, it goes from West to East by disappearing
but it has that special ability to travel from here to there appearing.
From our point of view, it goes from East to West in plain sight
Maybe it is
Your own shadow.
It travels from there to here shortening its length and eventually disappearing.
It travels from here to there appearing and subsequently increasing its length.
My initial thought is
Time always seems to disappear when you need it
There often seems to be a extra Time appearing when you are waiting around for something
Overall this makes:
A Time traveler
I guess it's
At one time it appears in a place and then due to its rotation it disappears and re-appears the next night.
Maybe it is
In the form of rain
It sounds like a
I can travel from there to here by disappearing, but I can also travel from there to here by appearing.
It sounds like this is describing quantum entanglement, where a particle will exist simultaneously in both locations until observed. When you observe one particle, the other paired particle's spin will be determined based on that observation. The reverse is also true.
This is my second approach. My previous answer pointed at something about we cannot say is invisible at all (as title suggests).
The better match is:
Lower air pressure or low tide.
It is invisible because:
Air is almost transparent. Although you can observe low tide living seaside but obviously you cannot see it, when you travel by ship.
It travels from there to here by disappearing:
When air/water flows towards us, the lower pressure/tide disappears.
It travels from here to there by appearing:
Opposite by analogy. :)
I can travel from there to here by disappearing
what was "there" would be "here" if the distance separating them vanishes
I can also travel from here to there by appearing.
and vice versa
Is the answer
airplane, because it disappears form the source airport after it takes off and appears on the destination airport after landing.
I highly doubt this is what you had in mind, but something that behaves like this is
A local change of a variable or a quantity in a system that tends to a global equilibrium.
In a physical system this could be e.g. pressure or temperature. If for some reason there appears a local change in, say, pressure (positive or negative), the change "travels" from here to there, i.e. the magnitude of the local difference in pressure decreases where it appeared and the magnitude of the pressure difference increases everywhere else, as the system tends to a new equilibrium.
Thinking about it the other way around,
if the "original" change suddenly disappeared (i.e. the reverse happens) the change would "travel" from there to here as the system again tends to the "original" equilibrium.
As an example:
For some reason a local pocket of overpressure appears: the system tends to a new equilibrium by distributing the pressure evenly, thus introducing overpressure (relative to the "original" state) everywhere else. Then at the same location a pocket of underpressure of equal magnitude to the earlier change is formed (meaning the overpressure "disappears" locally): the system tends to the original equilibrium by redistributing the pressure and thus the overpressure travels from everywhere else to "here".
Water my dudes. It goes from here (ground) to there (sky) by evaporation (disappearing). Then, it goes from there to here by appearing (rain).