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What if we make CPT transformation of free electron laser?

Duda Jarek

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In free electron laser(FEL) is used magnetic field to make electron move on sinus-like curve - thanks of synchrotron radiation and bosonic nature of photons is created coherent 'light' beam.


All fundamental equations of physics we use, conserve CPT symmetry, so imagine above picture from the point of view of such symmetry - we get position moving on this sinus-like curve in reverse direction, producing light beam ... photons traveling back in time!


To understand it, imagine 'standard' free positon laser - it produces photons which goes forward in time and space and finally hit into something, for example excitating its electrons.

If we look at it after CPT transformation - excited (anti)something produces photon (returning to ground state) - this photon goes to free electron laser and is absorbed.

To summarize - we see that usual free electron not only makes stimulated emission, but should also make stimulated absorption (be lasar). In FEL Such effect looks clear, but such effect should be observed also in cheaper lasers.


Usual photons will be most probably absorbed in some point of time, but photons 'traveling back in time' cannot hit ground state atoms (conservation of energy) - they have to hit already excited matter - we would have to prepare to allow for such emission (energy drain from future).

So to observe such effect, we would have to prepare the target by exciting it correspondingly (and continuously) - normally it should spontaneously emit photons in all directions, but if it would be hit by such photons 'traveling back in time', they should stimulate production of these photons in this direction.

We could cover the whole spherical angle but this direction by detectors and if this laser/lasar will be turned on, these detectors should observe decreased emission ... earlier then turning the laser on (by the length of optical way).


I've previously thought about using larger particles according to Feynman Stueckelberg, but using photons is much simpler and cheaper:




This picture is against our intuition - that we live in 'dynamic 3D' world - evolving 3D world with only pact->future causality relations...

Imagine throwing a rock into water - it creates waves running outside the middle ... but in fact these waves are resultants of statistics of microscopic movements which goes in both directions!

Big Bang can be imagined as such rock, which created 'waves of reality' which generally goes in one time arrow, what is observed in statistics as 2nd law of thermodynamics ... but it doesn't forbid future->past causality relations...

2nd law looks to contradict CPT conservation: assume we could proof that for assumed model of physics, there is mathematical property (entropy) which statistically always increase - assumed models of physics conserve CPT, so taking this transformation we get contradiction.

So this law isn't fundamental equation of our physics, but is property of its solution we are living in - artifact of Bigbang which created spacetime with relatively small entropy.


Our intuition is based on classical physics, but we know well that the world is more complicated.

I'll show briefly some (in fact - well known) arguments that physics is four dimensional - there are causality relations in both time directions:

- general relativity theory naturally operates on 4D spacetime and says that time flow is locally chosen by solutions. Einstein's point of view even allows to bend spacetime such that we create macroscopic time-loop - that means the future is already there...

- all fundamental equations of physics conserves CPT - that means that past and future are somehow similar...

- we are using equations of evolution of physics ... but didn't they come from Euler-Lagrange equations - optimizing some fourdimensional action ... ?

- other approaches of introducing physics uses usually path integral formulations: assumes that particles 'see' all possible trajectories...

- there is so called Wheeler's experiment:


In which after a photon passes two slits, we remove the barrier and place telescope far away to observe through which hole particle passed ... changing (later) its nature from wavelike into corpuscular...

- Bell's inequalities says that we cannot construct complete past->future causality theory with some hidden variables.


There is also new argument from statistical physics: Bolzman distribution is some fundamental mathematical law of statistics - QM should somehow correspond to it.

If we would use it to choose statistics in 3D, we would get something like p(x)~e^-V(x).

If we would use it to choose among paths going from past to this moment, we would get p(x)~psi(x), where psi is the ground state of hamiltonian.

If we would take Bolzman statistics among full paths, we would get p(x)~psi^2(x) as expected. The square means that both past and future 'halfpaths' has to agree in this moment.



For me these arguments clearly says that QM is just the result of fourdimensional nature of our world. So as in Wheeler's experiment - particles in fact travels through one trajectory - entanglement means that they haven't yet chosen - this choice will be specified in what we call future and if we know only past we can talk only about its probabilities.

When we make a measurement - we ask about the current value - it has to agree with both past and future path, which are the same - it's where the square comes from.


What do You think about it?

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  • 2 weeks later...

I've just accidentally found out that very similar picture gives

transactional interpretation of QM by John G. Cramer. You can find

very good links here:


It's being taught on the University of Washington.


If someone is interested in this discussion, here it has expanded:


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  • 1 year later...

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