If EM waves require no medium, why can't I get service at all times?

I have taken two years of high school physics and am very interested in RF communication. I know that electromagnetic waves do not necessitate a medium in order to propagate. Thus, shouldn't I be able to send/receive RF signals even when the signal is apparently blocked by things like mountains? I know most interference is due to incorrectly channelizing the correct wave from its assigned frequency. However, this is not an interference issue, right? Shouldn't there always be a path to the satellite(s)? I am only a rising high school senior, so I apologize if this is ridiculously simple... :)

• You are confusing "EM waves require no medium" with "EM waves can penetrate any medium". – user Jul 18 '16 at 8:57
• @MichaelKjörling hehe... very simply answered :) – MikeE Jul 18 '16 at 18:03

Electromagnetic waves do not necessitate a medium in order to propagate, but if medium is present it can enhance or degrade radio waves propagation.

In that matter you may recognize not just mountains as media, but buildings too, even atmosphere.

Satellites usually communicate using very high frequencies, such that require line of sight. Any hard object, including mountains or even buildings may block very high frequency radio-wave. If satellite is "visible" on the sky you can reach it by radio. Atmosphere does not have much influence on very high frequencies so it does not matter if it is cloudy, day, night, winter or summer.

I'd like to answer this from a perspective of high-level principles:

“Does not require a medium” just means that the wave can pass through vacuum, not that the wave never interacts with anything in its path. If the wave would pass through anything without interaction, then it would pass right through the receiving antenna, too and it wouldn't be useful for communication.

There are no exceptions in the laws of physics for antennas; there are just arrangements of matter that interact very little (vacuum or air), arrangements that have been designed to interact very strongly (antennas, reflectors), and everything else in between (trees, walls, mountains) which reflect, refract, or absorb the wave to some degree.

• I really like the sanity check "... it would pass right through the receiving antenna too." That's a wonderful way of arguing why we should think RF interacts with physical objects. – Cort Ammon Jul 19 '16 at 1:10

This is also a Physics question and the OP might consider posting under Physics.SE or at least a portion.

Actually, Electromagnetic Waves do require a medium and that medium is in fact called the Electromagnetic Field which is defined for all points in space-time. The area of physics known as QED (Quantum Electrodynamics) solves the problem of photon interactions with charged particles (e.g. electron) The photon is the quanta of the EM Quantum Field.

EM waves propagate in the EM Field and particles (photons) are excitations of the EM Field.

I know that the idea of a "Field" being the medium might be a bit obscure or abstract but it is indeed a reality as far as current Theoretical Physics is concerned. All forces and quantum particles are defined by quantum fields. The so called "physics" of the interactions is all in the field itself and fields interacting with other quantum fields.

The abstract notion of Space-Time and its geometry is also a field and the dynamics of this field are specified by Einstein's General Relativity field equations. But, it is considered a classical field, not quantum (at least not yet).