A reader questions the validity of claims made by Israeli researchers about their time machine model.
To the editor:
Regarding "Israeli researchers tout time machine model," just because something has appeared in Physical Review doesn't make it physically possibleonly physically publishable.
The concept of time as a "fourth dimension" is purely a mathematical artifact; it makes it possible to simplify the tensor calculus of general (and special) relativity. The same calculations can be carried out with the same result, but more tediously, by treating three spatial axes and one time axis separately. For example, Schroedinger used this approach when deriving his line element.
There is no theoretical basis for the idea that, like displacement on a positional axis, a negative displacement is possible on a time "axis".
All that relativity implies is that the INEVITABLE forward
displacement of events in time can proceed at different rates in different frames of reference. Attributing time reversal to general relativity or to Einstein is incorrect.
No one ever has demonstrated a fourth dimension, not to mention the fifth or higher dimensions necessary in which to "bend" time backwards.
Even the singularity at the location of a gravitational black hole is just a mathematical artifact: It reveals a problem with the math, not with space or space-time. There is a similar, very simple singularity anywhere one tries to use the inverse square law to determine the force (electric, gravitational, etc.) exactly at its "point" of origin.
All this argument is aside from the purely physical argument that an event not "moving" forward in time would violate energy conservation and the Second Law of Thermodynamics.
John Michael Williams
Senior Adjunct Faculty
Silicon Valley Technical Institute