Out of sight, and for most people out of mind, the physical world has
been vanishing. For over a hundred years quantum theory has shown that
the solid objects of the physical world are made of invisible energy
clouds. Atoms have no fixed physical properties until they are measured;
therefore, it remains to be shown why our world of everyday experience
feels solid in the first place. At the same time, other properties we
take for granted are dissolving. Einstein described time as dependent on
frames of observation. Now it seems that in the world of quantum
phenomena it can appear to move backwards.
This is a fascinating topic, and one that raises more questions about
things we take for granted. Quantum physicists at the University of
Vienna were looking at particles of light that are either entangled or
separable. These are technical terms going back to the era of Einstein
and Schrodinger. If two particles are entangled, they will exhibit
synchronized behavior no matter how far apart they are in space. As soon
as one particle is measured, its exact counterpart will show up in the
entangled twin state, even if they are far, far away from each other. In
other words, this "action at a distance" defies the speed of light.
Einstein could not accept the consequences of quantum entanglement, and
so he added the word "spooky" to action at a distance.
Yet quantum behavior is frequently spooky, and experiments have validated entanglement very soundly. In a recent article
a useful analogy was given. Two entangled particles are like a pair of
tumbling dice. If you stop one to see which number comes up, the other
dice must show the same number; it has no other choice. If the two dice
are separable, then the measurement of one doesn't affect the other.
Being separable seems normal to us. We never expect two dice to exactly
match. If they did, Las Vegas would go out of business, since chance
would disappear.
Now on to time. We expect time to move forward, the so-called arrow
of time. Past, present, and future constitute the normal progression of
events. For the same reason, cause precedes effect. It would be bizarre
to bleed before you cut yourself shaving or to hear a car crash before
the two vehicles collided. In the quantum world, however, certain
phenomena have arisen known as retro causation, and exactly as it
sounds, a future measurement appears as if it is affecting a past event.
This would be a form of entanglement that reaches backward in time, a
new form of spookiness.
Physics has depended for decades on "thought experiments," where a
new concept predicts what will happen before a physical experiment
proves or disproves the predicted result. In this case, the Viennese
team was working to prove "delayed-choice entanglement swaps." As a
thought experiment, this has existed for over a decade. Let us follow
the team's description closely:
Four photons, made of two entangled pairs, are produced (think of
them as four tumbling dice waiting to be measured). One photon from each
pair is sent to a physicist named Victor. He will be assigned the task
of measuring them. The two remaining photons are put in separate
packages, one sent to a physicist named Alice, the other to a physicist
named Bob. The three physicists now have their sealed packages of
photons that have not been measured yet.
Victor can choose between two kinds of measurements. If he decides to
measure his two photons in a way such that they are forced to be in an
entangled state, then Alice's and Bob's two photons also become
entangled. But if Victor chooses to measure his particles individually,
Alice's and Bob's photons end up in a separable state. This is a point
that Einstein was stuck on. He couldn't believe the assertion made by
Bohr and Heisenberg that the mere act of measurement by an observer
determines where a particle will be. But accepted quantum theory has
shown that particles have no physical characteristics until they are
measured. For a long time this has been true for position in space. Now
it seems that where a particle is in time also depends on measurement.
Modern quantum optics allowed the team to delay Victor's choice and
measurement with respect to the measurements which Alice and Bob perform
on their photons. As the lead author in Vienna describes it, "We found
that whether Alice's and Bob's photons are entangled and show quantum
correlations or are separable and show classical correlations, can be
decided after they have
been measured." In layman's terms, what you do today can affect what
happened yesterday. Or, perhaps, to put it in better way, the future
and the past are entangled, in a way that classical physics could not
explain it. The experimenters are working on a quantum scale billions of
times smaller than everyday events, and rather than claiming to change
the past, they say that their experiment "mimics" the effect of turning
time's arrow around.
So no one is saying -- yet -- that present causes can change past
effects. The mystery still remains over how entanglement, defying the
speed of light and now the arrow of time, actually relates to the "naive
classical world," which is to say, the everyday things we take for
granted. Our own bias is for expanding the observer effect more and
more, until science accepts that awareness is key to everything. We are
making reality through our role as conscious agents. But that's an
argument for another day -- perhaps yesterday if we get around to it.
Role of observer is very important ,for example we know for sure thar Sun rises in east and sets in west, but the truth is that Sun neither rises nor sets, since we are observing it from a revolving earth it seems to arise from east. 