Quantum Computing Discovery Reveals Time Moves Forward And Backward. Time behaves differently in quantum computing models. What is true at the quantum level is true for the rest of the universe as well.Using theoretical quantum computers, the researchers found that Causal Asymmetry does not exist in quantum models. They say that what applies to a quantum computer also applies to massive objects in the universe.

1. Arrow of Time
Causal Asymmetric in Quantum computing
Prof. Lili Saghafi
proflilisaghafi@gmail.com
@Lili_PLS
Applications of quantum computers and a quantum
internet
Lesson 4

2. Time Moves Forward And
Backward
• Quantum Computing Discovery
Reveals Time Moves Forward And
Backward
• Time behaves differently in quantum
computing models.
• What is true at the quantum level is true
for the rest of the universe as well.

3. What's long seemed to be true
• Time works in one direction.

4. Causal Asymmetry
• It is pretty obvious to everyone that time always moves
forward, never backward. It makes sense as 7:00 rolls
into 7:01, Monday into Tuesday, and middle age into
senior years and finally to death.
• This understanding of time also applies to classical
computers, which store information as either one of two
states, 0 or 1.
• It is far less challenging for computers to figure out what
will happen to the system in the future than to predict
what happened in the past based on the information it
has in the present.
• This is called causal asymmetry, the idea that a system
needs fewer resources to move forward than backward.
• In the real world, it is widely known as cause and effect.
• One thing happens now that results in another thing in
the future.
• What happens in the future cannot affect what happened
in the past.

5. Causal Asymmetry
• Information theorists have long assumed
that causal asymmetry is a fundamental
property of the universe.
• In 1927, astrophysicist Arthur Eddington
proposed that Causal Asymmetry is the
reason why time moves forward, not
backward.

6. Causal Asymmetry does not
exist in quantum models
• Using theoretical quantum computers, the
researchers found that Causal Asymmetry
does not exist in quantum models.
• They say that what applies to a quantum
computer also applies to massive objects
in the universe.

7. " Causal Asymmetry " demands
that it takes much more
information…
• A property of the universe that theorists
call "causal asymmetry" demands that it
takes much more information — and much
more complex calculations — to move in
one direction through time than it does to
move in the other.
• Practically speaking, going forward in time
is easier.

8. What does it mean?
• Meteorologists can do a reasonably good
job of predicting whether it will rain in five
days based on today's weather radar data.
• But ask the same meteorologists to figure
out whether it rained five days ago using
today's radar images?
• That's a much more challenging task, requiring a
lot more data and much bigger computers.

9. Causal Asymmetry
• Information theorists suspected for a long
time that Causal Asymmetry might be a
fundamental feature of the universe.

10. “Arrow of Time"
• If you understand the universe as a
giant computer constantly calculating
its way through time, it's always easier
— less resource-intensive — for things
to flow forward (cause, then effect) than
backward (effect, then cause).
• This idea is called the " Arrow of Time

11. “Arrow of Time"
The history of the Universe and the arrow of time.
Image credit: NASA / GSFC.

12. causal asymmetry disappears
inside quantum computers
• In certain circumstances causal asymmetry
disappears inside quantum computers, which
calculate in an entirely different way— Unlike
classical computers in which information is
stored in one of two states (1 or 0), with
quantum computers, information is stored in
subatomic particles that follow some bizarre
rules and so can each can be in more than one
state at the same time.
• Future research could show causal asymmetry
doesn't really exist in the universe at all.

13. the quantum models had no causal
asymmetry
• Very orderly and very random systems are easy
to predict.
• Think of a pendulum — ordered — or a cloud
of gas filling a room — disordered.
• The researchers looked at physical systems that
had a goldilocks' level of disorder and
randomness — not too little, and not too much.
(So, something like a developing weather
system.)
• These are very difficult for computers to
understand

14. the quantum models had no causal
asymmetry
• They tried to figure out those systems' pasts and
futures using theoretical quantum computers (no
physical computers involved).
• Not only did these models of quantum
computers use less memory than the classical
computer models, they were able to run in
either direction through time without using
up extra memory.
• In other words, the quantum models had no
causal asymmetry.

15. the quantum models had no causal
asymmetry
• While classically, it might be impossible for
the process to go in one of the directions
through time results show that in 'quantum
mechanically,' the process can go in either
direction using very little memory.

16. the quantum models had no causal
asymmetry
• Quantum physics is the study of the strange
probabilistic behaviours of very small particles —
all the very small particles in the universe.
• And if quantum physics is true for all the pieces
that make up the universe, it's true for the
universe itself, even if some of its weirder effects
aren't always obvious to us.
• So if a quantum computer can operate without
causal asymmetry, then so can the universe.

17. no asymmetry ?
• this research doesn't prove that there isn't
any causal asymmetry anywhere in the
universe.
• there is no asymmetry in a handful of
systems.
• But it's possible, that there are some very
bare-bones quantum models where some
causal asymmetry emerges.

18. cause and effect ?
• But it does appear that one of the key
building blocks of our understanding of
time, cause and effect, doesn't always
work in the way scientists have long
assumed — and might not work that way
at all.
• What that means for the shape of time,
and for the rest of us, is still something of
an open question.

19. The real practical benefit ?
• The real practical benefit of this work, is
that way down the road quantum
computers might be capable of easily
running simulations of things (like the
weather) in either direction through
time, without serious difficulty.
• That would be a huge change from the
current classical-modeling world.

20. References
• Arrow of time https://en.wikipedia.org/wiki/Arrow_of_time
• Where does our arrow of time come from? https://medium.com/starts-
with-a-bang/where-does-our-arrow-of-time-come-from-ecf5c3992fc2
• Experiment shows that arrow of time is a relative concept, not an
absolute one
• Quantum Correlations Reverse Thermodynamic Arrow of Time
https://www.quantamagazine.org/quantum-correlations-reverse-
thermodynamic-arrow-of-time-20180402/
• Causal Asymmetry in a Quantum World Jayne Thompson, Andrew J. P.
Garner, John R. Mahoney, James P. Crutchfield, Vlatko Vedral, Mile Gu
• Reversing cause and effect is no trouble for quantum computers
https://www.sciencedaily.com/releases/2018/07/180719094405.htm

21. Arrow of Time
Causal Asymmetric in Quantum computing
Prof. Lili Saghafi
proflilisaghafi@gmail.com
@Lili_PLS
Applications of quantum computers and a quantum
internet
Lesson 4