Expert: Philip A. Stahl - 1/16/2010

Question
My question is: do physicists view time as a real and independent entity or as a purely mathematically derived quantity?

I was taught classical Newtonian physics and mechanics in college. In my later years while postulating on the eternal human questions about the origins of the universe, I have become very curious about the use of time in physics as a real,tangible quantity.

My perception is that it is a variable completely dependent on some change of a real physical thing, either in position or internal state. We speak of the age of the universe in billions of years. The term “years” of course refers to the many rotations of the earth around the sun as the unit of measure (a change of position).  The distance to a star again uses the earth’s orbital circuit as the unit of measure, times the speed of light. I cannot in any real sense scoop up a bucket of time. I experience a thing we humans call time because of the observed rotation (change of position) of the earth and also of the change of the atoms of the physical body.  As I understand, the properties of matter at absolute zero are that there is no motion of any molecules or quanta, no energy exchange, therefore no time can be computed or imagined.


Thank you,
Ron
Savannah, Ga. USA


Answer
Hello,

Time is surely a physical unit (since we use it such so regularly in physics-astrophysics), but that doesn’t exhaust its meaning or the extent of its usage. It is also a dimension, referenced to space-time (as defined in Einsteinian special relativity) and it is conceivable that “time” as an objective (independent) property doesn’t even exist.

For example, the late physicist David Bohm, in his Stochastic Interpretation of QM (developed at a more or less popular level in his monograph, ‘Wholeness and the Implicate Order’- but presented in a series of papers with co-author Brian Hiley in 'Fundamentals of Physics') made the case that given quantum nonlocality (instantaneous connections demonstrated by the famous Aspect experiments) “time” doesn’t exist as a unit of reference or singular property. After all, if two events (say the inverse polarizations of photons, or the inverse spins of electrons) are instantaneously connected- then no time exists for any signal transit. In this case, time as a recognizable property ceases to be.

Bohm invoked a higher- dimensionality cosmos to build upon this theme, for example, positing that mass-energy and space-time are melded in at least a five dimensional entity. (Op. cit., p. 186, ‘Quantum Theory as an Indication of a Multi-dimensional Implicate Order’) What we perceive as instantaneous connections are really manifestations of that higher dimensionality.

Other physicists, e.g. Robert Nadeau, Menos Kafatos et al, have correctly observed that since time as an "observable" is susceptible to certain formulations of the Heisenberg Uncertainty Principle (e.g. its energy-time presentation) then time itself is uncertain, and if uncertain, no defined units or dimensions can be assigned. This also means time is elastic. It can bend, expand or contract, and even do so under the influence of consciousness. (See, ‘Conscious Mind in the Physical World’, by Euan Squires)

But the variable nature of time, and the fact it can’t be registered as an absolute was already known from special relativity. For example, for a person moving at 60% of the speed of light in a spacecraft, his clock time registers much more slowly in reference to a stationary Earth observer. For example, if four years were recorded for the Terran observer, only 3.2 years would be recorded for the astronaut travelling at 0.6c. At a speed of 0.95c, only 1.25 years would elapse for the traveler while the full four years would go by on Earth.

It is also very interesting that- from Maxwell’s theory of electromagnetism- we are fully enabled to make use of what are called “advanced potentials” defined in terms of:

V(r,t_a) = f1(r, T_a) and A(r, t_a) = f2(r, t_a)

Where t_a is the “advanced time”, t_a = t + r/c

And the f1, f2 are functions of the electric potential and vector potential,respectively.

In the advanced time formulation, we ascertain conditions for the future potentials based on the past, and are able to use them in appropriate calculations in the future. An evident violation of causality, though admittedly the sort of applications where these may be used are limited (for more on this, try googling Cramer’s offer and echo waves wherein the latter bear some similarity to advanced potentials and Cramer has devised experiments to detect them)

One of the most audacious claims has been rendered by G.J. Whittrow, 1972, The Nature of Time, Pelican Books, Great Britain, p. 103:

"the passage of time is merely to be regarded as a feature of consciousness that has no objective counterpart.”


And, of course, who can forget Stephen Hawking's use of "imaginary time" - using units of the imaginary number i (= sqrt(-1)).

The point being made here is there are many interpretations of time, and not all view it as an objective property - but more as a subjective one. (Like Whitrow's).

As to materials at absolute zero (if such temperature can actually be reached - as I understand it they can't since this would require an effective isolation of the system from the rest of the cosmos). But - say such materials could exist. Then, while it is still not true that all *molecular motion* would cease. There would be the quantum zero point energy.

For example, consider a diatomic molecule in the context of molecular vibration - and for which we can actually obtain vibrational spectra. In such a situation we observe defined and quantized levels viz.

---E3 = 7hf_c/ 2 ---f = 3

---E2 = 5hf_c/ 2 ---f = 2

---E1 = 3hf_c/ 2 ---f = 1

---E_o = hf_c/2 -----f = 0 (zero point energy)

Thus, in the absolute zero context, though levels E1......E_n may no longer be applicable, E_o still is. Hence, a residual minimal molecular energy (of vibration) is still there. It simply isn't available to be transferred to anything else!

Hopefully this all makes some sense to you!