BFTF GPBARC NEWSLETTER

G P Birla Observatory and Astronomical
Research Centre
Back From the Future
B.G. Sidharth

B.M. Birla Science Centre, Adarsh Nagar, Hyderabad – 500 063 (India)
In the 1930s there was a debate between Albert Einstein and Erwin
Schrodinger. Einstein’s Special and General Theories of Relativity oper-
ated in our usual spacetime and there was no possibility of super luminal
signals. In other words there was Causality, that is the son could not be
born before the father but there were experiments which seem to contradict
this notion (this has been explained in detail in [1]), leading to what Ein-
stein called Spooky Action at a Distance, as if the velocity of light barrier
had been broken. To understand the experiment let us consider the following
scenario: Two structureless and spinless particles which are initially together,
for example in a bound state get separated and move in opposite directions
along the same straight line. A measurement of the momentum of one of the
particles, say A gives us immediately the momentum of the other particle B.
The latter is equal and opposite to the former owing to the conservation law
of linear momentum. It is surprising that this statement should be true in
Quantum Theory also because the momentum of particle B does not have an
apriori value, but can only be determined by a separate acausal experiment
performed on it.
According to Classical concepts of spacetime, including the theories of rela-
tivity this would be important because it would imply that we know informa-
tion about one particle at the very instant that we measure this information
about the other particle. Hence Einstein’s characterisation of spookyness.
Schrodinger’s explanation was a principle which is called non separability.
When two particles interact at one point of time, they remain entangled for
all time, that is the two are no longer independent, that is they remain en-
1
tangled. This is a simple view of Space Entanglement.
It is a lot more subtle in the case of what may be called Time Entanglement,
which has been discussed in the recent past. Several gedanken have been pro-
posed by researchers for example from the Hebrew University of Jerusalem,
the University of Cambridge and so on, all of which point to this very strange
phenomenon which can be called Time Entanglement. To put it brie
y, ig-
noring the space part if an event happens at this instant then it can in
uence
itself after some time which is acceptable to our normal intuition. But here
recent work suggests that the particle at a future point of time can in
uence
the particle at the present time. Or to put it another way it was reported by
Megidish and his colleagues that in some strange way the future in
uences
the present or past. Or to put it another way they argued that there was
entanglement between photons which in terms of time did not overlap at all.
Heres how they did it. First, they created an entangled pair of photons, 1-2.
Soon after, they measured the polarisation of photon 1 (a property describ-
ing the direction of lights oscillation) thus killing it (step II). Photon 2 was
sent on a wild goose chase while a new entangled pair, 3-4, was created (step
III). Photon 3 was then measured along with the itinerant photon 2 in such
a way that the entanglement relation was swapped from the old pairs (1-2
and 3-4) onto the new 2-3 combo (step IV). Some time later (step V), the
polarisation of the lone survivor, photon 4, is measured, and the results are
compared with those of the long-dead photon 1 (back at step II).
The data revealed the existence of quantum correlations between temporally
nonlocal photons 1 and 4. That is, entanglement can occur across two quan-
tum systems that never coexisted.
Finally we would like to make the following comments:


According to Classical concepts of spacetime, including the theories of rela-
tivity this would be important because it would imply that we know informa-
tion about one particle at the very instant that we measure this information
about the other particle. Hence Einstein’s characterisation of spookyness.
Schrodinger’s explanation was a principle which is called non separability.
When two particles interact at one point of time, they remain entangled for
all time, that is the two are no longer independent, that is they remain en-
tangled. This is a simple view of Space Entanglement.
It is a lot more subtle in the case of what may be called Time Entanglement,
which has been discussed in the recent past. Several gedanken have been pro-
posed by researchers for example from the Hebrew University of Jerusalem,
the University of Cambridge and so on, all of which point to this very strange
phenomenon which can be called Time Entanglement. To put it brie
y, ignoring the space part if an event happens at this instant then it can in
uence itself after some time which is acceptable to our normal intuition. But here
recent work suggests that the particle at a future point of time can in
uence the particle at the present time. Or to put it another way it was reported by
Megidish and his colleagues that in some strange way the future in
uences the present or past. Or to put it another way they argued that there was
entanglement between photons which in terms of time did not overlap at all.
Heres how they did it. First, they created an entangled pair of photons, 1-2.
Soon after, they measured the polarisation of photon 1 (a property describ-
ing the direction of lights oscillation) thus killing it (step II). Photon 2 was
sent on a wild goose chase while a new entangled pair, 3-4, was created (step
III). Photon 3 was then measured along with the itinerant photon 2 in such
a way that the entanglement relation was swapped from the old pairs (1-2
and 3-4) onto the new 2-3 combo (step IV). Some time later (step V), the
polarisation of the lone survivor, photon 4, is measured, and the results are
compared with those of the long-dead photon 1 (back at step II).
The data revealed the existence of quantum correlations between temporally
nonlocal photons 1 and 4. That is, entanglement can occur across two quan-
tum systems that never coexisted.
Finally we would like to make the following comments:

  1. In the above scheme of things causality exists in a di erent sense. Any
    event could be the cause or could be caused by another event. This phe-
    nomenon can be picturised by a new Feynman type “spacetime diagram”.
    Let us consider a rectangular matchbox con guration for example (this has
    been discussed in (Cf.ref.[1])). There are two faces let us say ABCDE and
    FGHJ which are either facing us or facing away from us. Both the possibil-
    ities are valid depending on which face captures our attention immediately.
    In the present instance capturing of the attention rst corresponds to making
    an observation. So both possibilities are valid.
  2. The author proposed in 1997 a dark energy generated universe that could

    be accelerating [6]. At that time it was believed that under the in
    uence of
    dark energy the universe would decelerate and come to a halt. Fortunately
    the contra theory was veri ed very soon thereafter by the independent work
    of Perlmutter, Riess and Schmidt, which also got them the Nobel Prize. The
    picture here is of a universe submerged in a bath of dark energy rather like
    the more primitive model of Nernst at the beginning of the last century.
    From this point of view neither the Liebnitz nor the Newtonian concept of
    spacetime would remain intact. There is a holism which allows new phenom-
    ena.
  3. It must be observed that in the author’s work [6] the usual commu-
    tators of Quantum Physics are replaced by the so called Snyder-Sidharth
    relations. With these any two Quantum Mechanical observables like space
    coordinates, momentum coordinates or spacetime have non zero commuta-
    tors even thought these may be extremely small. We refer back to Dirac’s
    characterization of commutativity and compatibility: Two commutating ob-
    servables can be simultaneously measured but not if they non commutating.
    So with this new designation, there is entanglement all across the universe.
    Finally it may be observed that the author’s characterization of spacetime is
    di erent [7]. In this characterization spacetime intervals in the small are like
    steps or displacements in a Random Walk so that even if the number of steps
    forward equals the number of steps backward there is still a displacement that
    is non zero and it is this displacement which de nes space and time intervals.
    All the above considerations make time entanglement appear less severe than
    what it might appear. At the same time, it gives perspective to the phrase
    “super memory” being used by the researchers.
    (Based on the article in NAP 12 (1) 2018.)

    References
    [1] B.G. Sidharth, Chaotic Universe: From the Planck to the Hubble Scale,
    Nova Science, New York, 2001.
    [2] P.A.M. Dirac, The Principles of Quantum Mechanics, Clarendon Press,
    Oxford, 1958, p263.
    [3] A.S. Davydov, “Quantum Mechanics, Pergamon Press, Oxford, 1965,
    p.655.
    [4] B.G. Sidharth, Nonlinear World, 4 (2), 1997, pp.157-161.
    [5] C.W. Misner, K.S. Thorne and J.A. Wheeler, “Gravitation”, W.H. Free-
    man, San Francisco, 1973.
    [6] B.G. Sidharth, The Thermodynamic Universe, World Scienti c, Singa-
    pore, 2008.
    [7] B.G. Sidharth, Chaos, Solitons and Fractals, (12), (1), pp.173{178.