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.

Common Sense and Time

                                                              

Common Sense Island[1] 

Before I tackle the difficult task of explaining the nature of the Twin Paradox as promised in the previous post, I need to touch the problem of the common sense in science and everyday life.

For ordinary people, common sense is a good thing. This is our survival guide, our tool to get out of tricky situations. But this opinion is not shared by all, in particular by a part of scientific community.

The connection of time and the common sense is very important. We cannot have concept of time in conflict with our common sense. We either abandon science in its favour, or we turn the common sense off, or we can try to find out whether the two can be reconciled.

Before year 1905 despite continuous philosophical debates about the nature of time, general pubic had no sense of contradiction of the common sense temporal logic and real life. Newtonian physics has put time in the central position and has not added anything contradicting. The real problem with time and the common sense started after electromagnetic waves were discovered and mathematically described in the form of Maxwell Equations.
In year 1905 Einstein has published his article “On the Electrodynamics of Moving Bodies” . The world has changed ever since. The relativity theory took physics by storm. The outcome of the theory was of no immediate consequences to everyday life of ordinary people, but because it has changed the fundamental and common concept of time, the public at large got heavily engaged right from the beginning. In one of his letter Einstein bitterly remarks:

This world is a strange madhouse. Currently, every coachman and every waiter is debating whether relativity theory is correct. Belief in this matter depends on political party affiliation .

One of the main reasons for public debates was the challenge to the common sense. What is so disturbing in relativity that the common sense cannot handle?

Firstly it was enough to some people to be told that time flow depends on motion such that if one of twin brothers goes for a trip at sub-luminal speeds then returns, he will be younger than the stationary twin. This by itself is not illogical if the motion could slow down his metabolism. Yes, it is surprising but not unthinkable. Far more important consequences are that two distant events simultaneous for one twin, cannot to be simultaneous for the other. So coexisting twins while in motion live in somewhat different time realities – the realities that common sense cannot comprehend. It cannot also accept the thesis that there is no such thing as universal “Now”.

 And finally it appears that time travel is a possibility not ruled out by General Theory of Relativity. Genius mathematician Kurt Goedel came up with a specific solution of equations of General Relativity:

[…] by making a round trip on a rocket ship in a sufficiently wide curve, it is possible in these worlds to travel into any region of the past, present, and future, and back again, exactly as it is possible in other worlds to travel to distant parts of space. 

So, what did Einstein think about common sense while recognising these kind of outcomes of his work? He is believed to have said:

Common sense is nothing more than a deposit of prejudices laid down by the mind before you reach eighteen.

As we have see  has shown very little respect to the common sense which is treasured by the majority. Other scientists have followed suit. As pointed out by science writer John Horgan  :

many scientists came to see common sense as an impediment to progress not only in physics but also in other fields. […] the British biologist Lewis Wolpert declared in his influential 1992 book "The Unnatural Nature of Science," "I would almost contend that if something fits in with common sense it almost certainly isn't science." Dr. Wolpert's view is widely shared.

Such position is proliferating to all levels such that people taking part in online discussion forums may say something like that:

"Common sense" is precisely the thing that people use to refute science. Science is exactly the opposite of common sense. "Common sense" is simply the self-fulfilment of what you think you already know. 

But here is the twist: There is a famous Einstein’s quote: “God does not play dice”.

Following this lead we discover his letter to physicist Max Born where he writes:

You believe in the God who plays dice, and I in complete law and order in a world that objectively exists, and which I, in a wildly speculative way, am trying to capture. … Even the great initial success of the quantum theory does not make me believe in the fundamental dice-game, although I am well aware that our younger colleagues interpret this as a consequence of senility. No doubt the day will come when we will see whose instinctive attitude was the correct one.
[Letter to Max Born (7 Sep 1944). In Born-Einstein Letters, 146. Einstein Archives 8-207] 

This is an example of a strong non-scientific based statement tied to the belief system - the reasoning that sadly on this occasion seems to have failed in support to his own opinion about common sense which he was trying to apply. The quantum theory contrary to his predictions evolved with unparalleled success with randomness in the centre of it. But is the quantum theory the last word in science? The future will show.

There is however another example of Einstein’s reasoning which shows the bright side of the common sense.

In his Autobiographical Notes  he describes his thoughts when he was sixteen showing strong common-sense based beliefs:

If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as a spatially oscillatory electromagnetic field at rest. However, there seems to be no such thing, whether on the basis of experience or according to Maxwell’s equations. From the very beginning it appeared to me intuitively clear that, judged from the stand-point of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest. For how, otherwise, should the first observer know, i.e., be able to determine, that he is in a state of fast uniform motion?

This is the common sense in its pure form that gave birth to his famous theory, but this seems also true that it is based on prejudices laid down by the mind before he has reached eighteen.

In startling contrast is the description of common sense by Thomas Huxley:

Science is, I believe, nothing but trained and organised common sense, differing from the latter only as a veteran may differ from a raw recruit. 

From the above I understand that one can make statement about common sense depending on one’s definition of it. In my opinion Einstein defines belief system not the common sense while Huxley gets its real essence.  What it seems is that common sense is nothing else but logical thinking based on available facts. If you have right facts you cannot make a mistake. But what is when the facts are not so certain or incomplete. Can science and logic alone help to find right answers?

Both, science and common sense may fail in such circumstances. Science can admit insufficient data or it may cover up (temporarily) the deficiency and come up with pseudo solutions as it has done it many times in the past.

Relatively less publicly known but frequently discussed in philosophy of science is the example of so called Phlogiston Theory (PT). In the seventeenth century before discovery and understanding of chemical reactions with oxygen, it was postulated that there existed a fire-like element called phlogiston, which was contained in combustible matter and released during combustion. The theory could explain why some substances burn more eagerly than others. The problem has emerged after it has been discovered that the weight of the ashes of a burned metal such as magnesium is more than that of the metal alone before burning. The common sense then would indicate that the theory was wrong, but the scientific solution of the paradox put forward by proponents of the PT tried to overrule the common sense by adding a conjecture that the phlogiston has negative weight. Why not? We know today this is the oxygen combining with other substances causes burning and weight increase. The moral of the story is that what is now scientific and logical does not have to be true tomorrow and we have to be very cautious about it.

Common sense becomes more formalised with the advances of Artificial Intelligence theories. Base on definition given by McCarthy in the context of computer programs, I can say that:

 Common sense is the ability to deduce a sufficiently wide class of immediate consequences of anything one is told and what one already knows. 

So this is more that logical thinking. It may include all available tools of intellect such as analogy, statistics, heuristics, plus wide range of knowledge. We can now see even better that Einstein Special relativity was the product of his common sense despite his later sarcasm.

In such context I do not see how common sense can be an obstacle to understand problems resulting from the theory of relativity. I think it is a great tool if used with open mind and acceptance that it is not fully immune to illusions. Any contradiction with the theory requires reconciliation not abandonment of one of the contradicting factors.

#CommonSense

[1] Picture: Commonsense Island Courtesy http://commons.wikimedia.org/wiki/User:Artaxerxes