# Mobile communication with electromagnetic waves and theory of relativity

• shyamalshukla
In summary, electromagnetic waves travel at the speed of light, leaving no component for time. This means that the time on a watch on a beam of electromagnetic wave does not change at all. When considering spacetime as a book with events arranged in a region of space, two users U1 and U2 can move to different pages (corresponding to different times) while the wave remains on the same page. This raises the question of how the two users are able to communicate with each other, as they are never on the same page of the spacetime book. This is due to the fact that the concept of "pages" is relative and depends on how one chooses to slice spacetime. From the perspective of a photon, the entire book
shyamalshukla
Since the combined speed of electormagnetic waves can be 'c' and that they travel in space at 'c' leaves no component for time, hence the time on a watch on a beam of electromagnetic wave does not change at all.

With this understanding, assume two stationary mobile phone users U1 and U2.

U1's mobile phone emits an electromagnetic wave at time T1 which according to U2's watch reaches him at T2. However, as per the wave, it is still time T1.

Considering spacetime to be a book with events in a region of space R being arranged as pages of the book according to the time at which they occurred (T1 and T2 are 2 different pages of the book), U1 and U2 have moved to the page corresponding to time T2 while the wave always remains in the page correspoding to time T1.

Now how are the two users U1 and U2 ever able to communicate with each other? The wave and the recepient are never on the same page of the spacetime book.

shyamalshukla said:
Since the combined speed of electormagnetic waves can be 'c' and that they travel in space at 'c' leaves no component for time, hence the time on a watch on a beam of electromagnetic wave does not change at all.
A watch could never travel at the speed of light...

shyamalshukla said:
Considering spacetime to be a book with events in a region of space R being arranged as pages of the book according to the time at which they occured
For that analogy to be applicable, there would have to be absolute time and absolute space - a "preferred" reference frame. Relativity showed that that is not the case.

diazona said:
A watch could never travel at the speed of light...

Ok, let's just leave out the watch. That was put into indicate that no time has passed as per the wave and it still T1 according to it.

diazona said:
For that analogy to be applicable, there would have to be absolute time and absolute space - a "preferred" reference frame. Relativity showed that that is not the case.

Accepted that there is no absolute space and no absolute time, but there is absolute spacetime and this spacetime does have different events on difference slices of spacetime.
Hence the two users would have moved to a different slice of spacetime

shyamalshukla said:
Since the combined speed of electormagnetic waves can be 'c' and that they travel in space at 'c' leaves no component for time, hence the time on a watch on a beam of electromagnetic wave does not change at all.

With this understanding, assume two stationary mobile phone users U1 and U2.

U1's mobile phone emits an electromagnetic wave at time T1 which according to U2's watch reaches him at T2. However, as per the wave, it is still time T1.

Considering spacetime to be a book with events in a region of space R being arranged as pages of the book according to the time at which they occurred (T1 and T2 are 2 different pages of the book), U1 and U2 have moved to the page corresponding to time T2 while the wave always remains in the page correspoding to time T1.

Now how are the two users U1 and U2 ever able to communicate with each other? The wave and the recepient are never on the same page of the spacetime book.
While it is "still T1 per the wave" it's also true that it was "already T2 per the wave" when the wave was emitted. T1 and T2 are the same "page" per the wave, using your analogy.

shyamalshukla said:
Now how are the two users U1 and U2 ever able to communicate with each other?
With a little bit of lag.

shyamalshukla said:
Ok, let's just leave out the watch. That was put into indicate that no time has passed as per the wave and it still T1 according to it.
The point is that no physical system capable of measuring the passage of time (that's what we mean by "clock" or "watch" in relativity) could ever travel at the speed of light. A photon has no concept of time.
shyamalshukla said:
Accepted that there is no absolute space and no absolute time, but there is absolute spacetime and this spacetime does have different events on difference slices of spacetime. Hence the two users would have moved to a different slice of spacetime
Yeah, but then the question of whether or not two events are on the same slice depends on how you choose your slices. There is no one special "correct" way to slice spacetime. The book analogy is a bad - well, misleading - one because it makes you think that the particular way events are grouped on to pages of the book is The One True Way Of Slicing, but that's just not the case. (Everybody takes a while to get used to the concept )

Al68 had a decent way of putting it, I think. I suppose you could say that from the photon's "perspective" (photons don't really have a perspective, but whatever), the entire book is all on one big piece of parchment. And as you can imagine, the concept of "pages" makes no sense when there's just one of them.

## 1. What is the relationship between mobile communication and electromagnetic waves?

Mobile communication relies on the use of electromagnetic waves, specifically radio waves, to transmit signals between devices. These waves travel through the air at the speed of light and are able to carry information such as voice, text, and data. Mobile devices, such as cell phones, use antennas to send and receive these waves, allowing for wireless communication.

## 2. How does the theory of relativity impact mobile communication?

The theory of relativity, proposed by Albert Einstein, states that the laws of physics are the same for all observers in uniform motion. This theory has been proven to be true and has a direct impact on the functioning of mobile communication. The theory allows for precise measurements of time and distance, which are crucial for the accurate transmission and reception of signals in mobile communication.

## 3. Can the theory of relativity affect the speed of mobile communication?

Yes, the theory of relativity does affect the speed of mobile communication. As stated before, the theory allows for precise measurements of time and distance. In mobile communication, this means that the speed of signals can vary depending on the relative motion between the devices and the observer. However, the difference is so small that it is not noticeable in everyday use.

## 4. Are there any risks associated with using mobile communication and electromagnetic waves?

There are some potential risks associated with prolonged exposure to electromagnetic waves, such as those emitted by mobile devices. However, the scientific community has not reached a consensus on the level of risk and more research is needed. Currently, regulations and guidelines are in place to limit exposure and ensure the safety of mobile communication users.

## 5. How does the use of electromagnetic waves in mobile communication differ from other forms of communication?

The main difference between mobile communication and other forms of communication is the use of electromagnetic waves. Unlike other forms, such as wired communication, mobile communication does not require physical connections between devices. This allows for more flexibility and convenience, but also poses a potential risk for interference and signal loss in certain environments.

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