This can be seen when any of them are talking with each other or especially when they are embracing each other. Does that mean that the communication is happening instantly, therefore faster than the speed of light?
Short answer, no, they don't need to be communicating faster than the speed of light to accomplish what we see in the show. Long explanation follows.
The only time I recall us seeing what we need to answer this is when Will and Riley speak on the phone while also sharing. We see them interact via their connection faster than the cell phones, but it's pretty close, the cell phones are like an echo.
At the time, I believe Riley was in London, and Will was in Chicago. That's 3,945 miles (across the surface). The Earth's radius is 3,959 miles. Doing some math, that means that the straight line distance between London and Chicago is ~3784 miles (burrowing through the Earth), and the speed of light is 186,282 miles/sec, so a speed of light direct connection would take 0.020313 seconds. So about 20 millisecs.
I couldn't find a solid figure on cell phone lag between the US and UK. I did find this post which suggests we're dealing with a lag on the scale of hundreds of milliseconds at best.
For an audible echo, you need an absolute minimum of 1/15th of a second gap between the sounds, which is .0666666 seconds.
So the sensates can, at worst, communicate at roughly the same speed as we route cell phone calls around the surface of the Earth (or via satellite) to match what we see in that scene, which is well under the speed of light. Therefore, no need to assume they can communicate faster than the speed of light. They can be communicating well under the speed of light to pull off what we observe in the show.
Though it's not explicitly stated in the series, there are scenes where the action outside of a "linked" conversation is dramatically slowed. This does give us some context at the speed the sensates can communicate.
examples from episode 1x10:
- Wolfgang is on his knees during the gang fight. He is asked a question by his cousin with a gun to his head. At this point, Lito 'shows up' and he and Wolfgang have a 1 minute conversation while the events in the background move very slowly. When everything resumes, it appears that only a couple of secondshave passed.
- Lito is fighting Hernando and being beaten. While laying on the ground, Wolfgang appears to help him up and offers to take over. During this interraction, we see Hernando dragging Daniela away in slow motion while conversation is happening in 'real time'
While the 2 sensates are communicating, everything else is moving at a very slow rate, but not frozen. If communication was at light-speed, it would be near-instantaneous and we'd see the surrounding events be frozen.
No, they do not communicate at the speed of light..
Considering the reference of outside events being super slow, I believe they can have full conversations at the speed of thought.
No, it does not appear they are communicating faster than light. Nor would they need to. And even if they were, you would not be able to determine it unless one of them was living off-planet to confirm it.
- All of our known electromagnetic communication phenomena take place at the speed of light and experience delay only when there is an interaction with a technological medium supporting or relaying the signal.
Electromagnetic waves are created by the vibration of an electric charge. This vibration creates a wave which has both an electric and a magnetic component. An electromagnetic wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s (a speed value commonly represented by the symbol c). The propagation of an electromagnetic wave through a material medium occurs at a net speed which is less than 3.00 x 108 m/s. (REF: The Physics Classroom)
Since it doesn't appear to matter whether the Earth is in between two communicators, whatever their communication uses for a transmission medium is NOT delayed by the mass or interference of the planet, itself.
You do not need faster than light communications on the surface of a planet. The speed of light is fast enough for real-time communication. The only time it wouldn't be is if you were communicating between stellar bodies such as the Moon or other planets in the solar system.
If for example, one of the cluster were to be standing on the moon and did not have any form of noticeable delay, could you make the case for instantaneous communication because there was NO lag in their signal.