There Is No Such Thing as "Now" - So They Say...

There is hardly any more obvious experience than the awareness of "Now". It is with you all day and often even while you sleep. "Now" is more like one snapshot of the movie at a time - visually. When it comes to thoughts and sounds it is not immediately clear. There is no such thing like instantaneous sound as there is an instantaneous image. You need at least one period of oscillations to say there is a sound. This is quite mysterious but this is not that kind of problem discussed in physics.

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The concept of "now" we have we project to all visible space. Looking at the Moon we could say it is there now but it is not exactly there. It is by one second further away from the currently viewed position. And who knows where are those stars now that are said to be located millions light years away. We do not have problem with that. There is always some transport delay. But after year 1905, some scientists boldly claim there is no such thing as universal "Now" merely because we do not know any signal that instantaneously propagates everywhere. The fastest known speed is the speed of light.
Common sense embraces the concept of “Now” which has the universal meaning for most people around the globe and in principle it means state of permanent simultaneity of all changes of states of coexisting physical objects. With the arrival of relativity and after declaring simultaneity as relative the common concept has been questioned as something that has no place in reality. Probably the most decisive statement has been made by Arthur Eddington:

 Suppose that you are in love with a lady on Neptune and that she returns the sentiment. It will be some consolation for the melancholy separation if you can say to yourself at some—possibly pre-arranged—moment, “She is thinking of me now”. Unfortunately a difficulty has arisen because we have had to abolish Now. There is no absolute Now, but only the various relative Nows differing according to the reckoning of different observers and covering the whole neutral wedge which at the distance of Neptune is about eight hours thick. She will have to think of you continuously for eight hours on end in order to circumvent the ambiguity of “Now”.

There are some objections which may be raised to the above:

1. What is the relevance of relativity when two distant observers are not in relative motion?
2. Does the relativity theory demonstrate mathematically irrelevance of “Now”?

The answer to those questions is negative as it will be shown below. Einstein’s position on abolished “Now” was not that enthusiastic and obvious as for Eddington. This is reflected by records of his conversation with Rudolf Carnap who wrote:

Once Einstein said that the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation.

The problem worrying Einstein was the incompatibility of physical and psychological aspects of time and related phenomena. I am worried whether alleged incompatible physical aspects of time are real or just misconceptions.

Where is “Now”?

From my philosophical point of view, “Now” is an instance of existence. One has to have the concept of instance as well as that of existence. This is not straightforward and difficult but not impossible to bind such definition directly to the Special Theory of Relativity (STR). We need to find a simpler way.

Following Einstein’s seminal 1905 paper we find important clues.

If we wish to describe the motion of a material point, we give the values of its co-ordinates as functions of the time. Now we must bear carefully in mind that a mathematical description of this kind has no physical meaning unless we are quite clear as to what we understand by “time.” We have to take into account that all our judgments in which time plays a part are always judgments of simultaneous events.

This is sufficient to define local time in arbitrary locations but insufficient for physical purposes if one wants to compare or order occurrence of events at distant locations. For this Einstein states:

But it is not possible without further assumption to compare, in respect of time, an event at A with an event at B. We have so far defined only an “A time” and a “B time.” We have not defined a common “time” for A and B, for the latter cannot be defined at all unless we establish by definition that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A.

Later on Einstein defines distant clocks synchronization method and concludes:

Thus with the help of certain imaginary physical experiments we have settled what is to be understood by synchronous stationary clocks located at different places, and have evidently obtained a definition of “simultaneous,” or “synchronous,” and of “time.” The “time” of an event is that which is given simultaneously with the event by a stationary clock located at the place of the event, this clock being synchronous, and indeed synchronous for all time determinations, with a specified stationary clock.

After all elaborated explanations he comes to a conclusion which is what we already know:

We have one reference clock (say at the origin of a coordinate system in   physical space) of which indications are representative to any point in space given distant clocks are properly synchronised. 

Without much of philosophy here any instance of the clocks determines definite now anywhere in the universe. So “Now” is clearly omnipresent. What is then the reason for concern? Nothing new that we have not been aware already.

The STR categorically insists: any inertial observer can consider himself stationary and has the common time determined by a reference clock. 

If this is the case, to trigger simultaneous process at distant location requires no clock synchronisation but a simple operation with light beams as illustrated on this diagram

First establish distance d to a location (Neptune) and set up a process that can be triggered by an arrival of the laser ray. Compute time to destination as d/c. Set a clock to –d/c while sending laser pulse to destination d. At time t=0 start a process at origin 0. At the same time laser pulse arrives at d (Neptune) and starts the twin process and both continue synchronously. 

To verify synchronicity, the distant process may send a laser pulse back after two cycles which should arrive at origin precisely after two cycles This way the lady on Neptune may drink champagne at cycle 2 together with the observer at 0 to celebrate successful distant simultaneity experiment.

If that is not enough, imagine a laser at equal distance from 0 and d which sends simultaneously two beams in th opposite direction. This can trigger simultaneous celebration too. Pre-relativity physics would object to such scenario due to concerns that we do not know the speed of the system with respect to ether, but no such thing like ether or a common medium for EM waves seems to exist hence 

“Now” is everywhere, alive and well for a stationary system.