# Is it possible to build a Backward Time Viewer?

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As everyone knows, there are many doubts if backward time travel can be possible, since it raises many paradoxes of which the most known is probably the Grandfather paradox.

My question is the following: "According to the current state of our Physics knowledge, there is something that prevents us to build a Backward Time Viewer?".

By Backward Time Viewer I mean a machine which can display events occurring in an arbitrary date in the past (not necessarily in an arbitrary location). Clearly, this is not a precise definition, but I think is better to leave you some freedom to choose a precise definition as part of your answer.

I am not a physicist, but I thought that a Backward Time Viewer can be in contradiction with Heisenberg uncertainty principle in such a way: We measure with arbitrary precision the position of a particle at time 0. Then, at time 1, with a Backward Time Viewer we measure with arbitrary precision the velocity at time 0 of the particle. Thus we can obtain the position and velocity of the particle at time 0 with arbitrary precision, in constrast with the uncertainty principle.

Closed as per community consensus as the post is popular physics question
asked Nov 17, 2014
recategorized Jun 21, 2015

Hi Charve,

PhysicsOverflow is a graduate-level and above physics site, which means that it is for advanced students and physicists. This seems rather a popular physics question, targeted at a general audience. I am therefore voting to close.

Hi Dilaton,

actually I do not see how my question is not of interest for graduate-level or above physicists. Surely, to understand the question itself are not required any graduate-level knowledges. However, I think that the problem is not trivial and that a precise answer needs deep knowledges of a large spectrum of Physics.

A "backward time viewer" could be consistent with the uncertainty principle, if it was restricted by the usual limits to precise measurement. For example, if accurately measuring the position of the particle now, made it impossible to measure its velocity in the future, using the viewer.