Comment on* “Time Reborn: from the crisis in physics to the future of the universe”*

Time is real, okay! A time-sequence is essential for the causality principle. Good that Lee Smolin comes out against “laws of physics” that take time to be an illusion. We know the laws are man-made. As he writes, light-rays reach us only from the past, not the future, so the ‘laws’ should encompass this.

The time coordinate in Maxwell’s electromagnetic theory is different from the 3 space coordinates. The beauty of the 4-vector differential formulation, with ‘imaginary’ time the 4^{th} coordinate, has led people astray.

The time-explicit formulation of light waves uses (Liénard-Wiechert) retarded potentials to form an integral over waves reaching each point from earlier times. This satisfies the Penrose criterion for a truly fundamental law being irreversible, unlike the differential equations of Maxwell.

If general relativity (GR) is to encompass gravity and electromagnetic fields, as is often claimed, it must be formulated so as to cover travelling waves. It cannot depict them as sources of energy-mass that distort the geometry of space.

There has been progress in reformulating GR, in identifying a real energy-momentum tensor (not the pseudo-tensor of Einstein) which describes fields and associated waves carrying real energy through space – not across space, as in theories of photons. Defining a real tensor requires, however, the choice of a preferred metric, ie. with coordinates for real space.

Some leading physicists of the mid-20^{th} Century (Vlad Fock, Steven Weinberg) saw it as essential to define a real energy tensor in GR, and were ready to adopt real space coordinates. They were largely ignored by the abstract theorists, including Smolin. Time now for him to acknowledge both real time and real space!

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*Related*

Raymond Tallis, philosopher, issued a challenge in the Guardian (27 May) over the mishandling of ‘time’ and covered several other points explored in our blog: Far from having replaced metaphysics, science is in a mess and needs help. The dismissive “Just shut up and calculate!” to those who are dissatisfied with the incomprehensibility of the physicists’ picture of the universe is simply inadequate. http://www.guardian.co.uk/commentisfree/2013/may/27/physics-philosophy-quantum-relativity-einstein

The responses with 800 Comments from readers show this onslaught on theoretical physics by Tallis struck many chords.