Time in physics and experienced time

Two main issues were addressed at the final discussion of the Physics Workshop of the second phase of the Intercontinental Academia (ICA), on March 9: the difference between the concept of time in physics and the perception of time by living organisms, and the invariable aspects of time in relativity.

Eliezer Rabinovici

For physicist Eliezer Rabinovici, from the Hebrew University of Jerusalem and a member of the ICA's Senior Committee, whoever speaks the physical-mathematical language clearly sees what it means to add time as an extra dimension and the implications of having four dimensions. "The time dimension has different characteristics, but can be called so as it is a mathematical term. But it becomes confusing to talk about the fourth dimension in ordinary language, so it is best not to use the expression."

Physicist Naoshi Sugiyama, associate director of the Nagoya University's Institute for Advanced Research (IAR), commented that dimensions are numbers required to specify the existence of something. As an analogy to the four dimensions of spacetime, he said that if someone needs to tell a friend how to find them, they will tell them the building address, the correct floor and the time when they will be there.

Naoshi Sugiyama

Taking part in the discussion on the perception of time and the time in physics, physicist Peter Goddard, a researcher and former director of the Princeton Institute for Advanced Study, said that to relate everyday experiences with what happens beyond can be confusing: "As humans, we can not have the experience of special relativity, because we can not travel at the speed of light."

Another mistake, he said, is to claim that something exists independently of the observer. "In the Newtonian thinking structure, space and time were considered uniform. One can not include relativity in this structure. What does exist at any given time? The answer to that depends on the observer."

Chemist Hisanori Shinohara, Director of the IAR, recalled that the 2nd Law of Thermodynamics predicts the increase of entropy in an isolated system and asked if time will still make sense when the entropy of the universe as a whole ceases to increase, with it reaching a perfect state balance and, consequently, dying.

Sugiyama said that one can not predict the temperature and the time of the universe if we think of an infinite future. Moreover, "if there is dark energy, the universe will expand forever and in that sense will never come to an end." On the other hand, "if there is no dark energy and the universe is flat, it will stop expanding at some point, but this will be in an infinite future."

Hisanori Shinohara

Rabinovici has also commented on the issue exposed by Shinohara. He said that, in fact, entropy increases permanently, but it depends on the analyzed system. According to him, even in the universe the existence of long periods of increasing entropy and other ones of decreasing entropy should be considered: "And in a time far, far away, the universe will again be what it once has been. But I say to young students that this kind of issue is very deep and it is best to leave it aside for now and concentrate on simpler ones."

Sugiyama said there is a famous analogy about the return of the universe to a previous condition: "A monkey hits the keys of a typewriter. If it does this for a long, long time, it will evolve to Shakespeatre by chance."

Anthropologist Naoki Nomura, from the Nagoya University, has also participated in the discussion. In his view, the idea of relativity does not belong only to the physics but is also a matter of epistemology. He has even questioned the consistency of the theory of relativity: "When it previews a single nature for time it stops being relative and becomes contradictory."

Naoki Nomura

When responding to the comments by Nomura, Rabinovici said that one of the dangers of this type of workshop "is the use of words because they mean different things to each person." He added that the term relativity was incorporated into the theory's name wrongly: "It is not a theory of relativity but a theory of invariance. In the process of searching for what is not relative, one discovers that many things considered invariable are actually not. Newton thought that some things were absolute, when they are actually relative. But not everything is relative. The order in time (something happening after another), this can not be negotiated. If two things are simultaneous while measuring time or not, this is negotiable, and it depends on certain factors."

Goddard also commented Nomura's statement: "The personal experience of time is one thing and the time in physics is another. The theory of relativity is consistent and has nothing to do with the subjective experience. It is very important to keep these separate."

Peter Goddard

Martin Grossmann, former director of the IEA and also a member of the ICA's Senior Committee, wondered whether Goddard finds it impossible to relate time in the way it is thought in physics with the way it is seen by social sciences and humanities.

Goddard said that it is not impossible, but that one has to be careful with the words, as Rabinovici said. In his opinion, the confusion in the use of terms of one area in another one are partly the fault of the physicists who "like to use figurative speech, because metaphors can be quite productive while doing science."

Valtteri Arstila, from the University of Turku, wanted to know the opinion of Goddard about a text on spacetime that has been published at the Stanford University's website. According to the text, the general theory of relativity makes the spacetime less relative than the one in special relativity: "The absolute space and time of Newton are kept. They are merely amalgamated and enriched with the most flexible mathematical skeleton."

Valtteri Arstila

Goddard did not agree with the statement by Stanford. For him, time does not cease to be relative in the general theory of relativity because there is a "symmetry between mass and geometry of spacetime, given that Einstein conceived the intensely related spacetime and matter."