Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Quantum Interest Conjecture and negative energy-density

  1. Feb 12, 2017 #1
    Hello, everyone. I've been trying for quite some time to figure out what's up with the paradigm of quantum interest conjecture and the possibility to generate negative energy (even only theoretically speaking). Only from pure interest I have read a bunch of papers on the matter, however I feel a little bit confused. I should mention that I understand the very basic and principle logic/concept behind those studies and also I understand higher mathematics but I lack the needed specific knowledge about quantum mechanics and special relativity since I am no physicist (only mere mechanical engineer :P ).

    In general, quantum inequalities dictate that a negative pulse of energy must always be followed by a bigger positive one (that is quite understandable and logical). Also, the negative one can be arbitary big, but the higher it's energy density, the shorter the duration of the pulse. And also it must be contrained in tighter space.

    My first question is - are the inequalities proved for all types of known fields and for all types of space-times, especially our own 3+1d ?

    Second, are there verified (mathematically/theoretically) cases of violations of those rules ? For instance, there seem to be several cases which allow negative energy densities (some are natural): Casimir effect (where the negative energy region exists statically indefinitely long), the Hawking radiation from black holes, the Ford-Svaiter parabolic mirror, dark energy which drives the universe's expansion.

    Third, when going through different papers and researches it seems there are some physicists which advocate the QIn (like Ford who proved them), and others who either argue that the inequalities don't always hold, or make mathematical modifications to the equations (for example the type of the used sampling function, etc). Since the question of the existence of negative energy-density almost always refers to the possibility to create warp drive, worm-holes and so on, we have scientists like Kip Thorne or Krasnikov who seem to be in the "opposing team". There are also others like Felippe Loup (he has few interesting papers on the matter of Natario warp drive solutions) who shows with some modifications to the bubble shape function that it will be possible (at least theoretically) to make such space-time configuration without violating the quantum inequalities. So, in general, who is "more" wrong and who is "more" right (figuratively speaking)? As I see it, any of those scientists uses tools and aspects of the theory which are actually prohibited by the known physics.

    And lastly - I would like to know if the following hypothetical setup would work (if we take in to account the quantum inequalities): Let's presume that we have source of squeezed light (it is verified that an electromagnetic wave after "squeezing" would have alternating regions of higher positive and small negative energy segments, so summary - it's energy is still positive). Would it be possible to create via a mirror and source a standing "squeezed" light wave in order to "fix" spatially the segments ? And if this is possible, then could one arrange several standing waves, angled to one another, so that all of them intersect at a certain negative density segment ? Would this boost it's local density (of course with the price of denser positive energy pulses elsewhere, for example at the ends of the wave, to balance) ? And to finish this mind experiment - let's presume that we either have this setup (if ever possible), or the already mentioned Ford-Svaiter parabolic cylinder mirror (according to Ford's paper it allows local concentration of static/constant negative energy density near it's focal line). Now, the QIC governs that a pulse of negative energy can have higher density but for shorter time. What would happen if we turn on and off our "source" of negative energy (in one of the two mentioned setups) with high frequency ? Is it acceptable to think that at some local region a shorter pulses but with high density, if alternated with high enough frequency, would simulate relatively constant in time and arbitary high value of the energy density (as if the quantum inequalities didn't hold)? As I understand it the QIC wouldn't be violated, but only for the single pulse. However we would have non-stop series of pulses. The source, the light wave and the local space region create sort of closed system (in the duration of one pulse) for which the ineaqualities are valid. However, if we alternate the pulse dynamically (turn on and off the wave), or even imagine that for any given pulse we use different source aimed at the same local spatial region (it doesn’t matter, it would lead to the same avail), then the system is no longer closed and the effect should be as if we have on average one continious in time, locally static and with high density pulse ?

    P.S. - I should apologize for any grammatical errors (english is not my native language).
  2. jcsd
  3. Feb 12, 2017 #2


    Staff: Mentor

    What is this? Do you have a reference?

    References/links please?

    What inequalities?

    Please give more specific information and references; your question is not answerable as it stands as it's not clear what you are talking about or where you are getting your understanding from.
  4. Feb 13, 2017 #3
    I thought that this matter is relatively popular in the physics community. I'll make add-up to my post.
    So, Ford, Pfenning, Roman and other researchers reached the conclusion that negative energy density, which exisatence quantum field theory allows,
    should get spatial and temporal restrictions. As it seems they believe no macroscopic quantities of negative energy density should exist because
    such a phenomenon could allow the creation of anomalous (atleast from their perspective) entities like warp drives, wormholes, time machines and other exotic solutions to the Einstein's equations. With this intention in mind they derrived mathematicaly a group of inequalities (anologous to Heisenberg's uncertainty principle) which set boundaries for the energy density in a couple of different space-times. That's the main idea. You can see the original paper here [https://arxiv.org/pdf/gr-qc/9711030.pdf].
    In addition to the QIC matter I can also add this paper as reference [https://arxiv.org/pdf/gr-qc/9901074.pdf]. It is from the same authors.
    On the contrary, there are attempts to prove that restrictions placed by the quantum inequalitities don't always hold. I'll refer as example to one such paper [https://arxiv.org/ftp/arxiv/papers/1007/1007.3258.pdf]. Also as I mentioned in my first post there are physicists who asume different initial conditions and prove that the necessary negative energy density needed for a warp drive solution could in fact be achieved within the boundaries set by the QIC. I named as an example the work of Felippe Loup, so here it's the paper: http://www.rxiv.org/pdf/1209.0049v1.pdf .
    I found some time ago an AIAA paper from 2012 which summarizes the latest of the analysis on the possibility of warp drive propulsion, which includes also the features of the QIC - [https://www.google.bg/url?sa=t&rct=...p7Pprc83xDOI4HiKQ&sig2=e3I1v0sMKzkY5K3272BGIQ]. At the end of this paper there is a huge list of references to other literature sources and papers, which are all related to the topic. The Ford-Svaiter parabolic mirror is also mentioned several times in the paper. One can see the original material from Ford and Svaiter here: [https://arxiv.org/pdf/quant-ph/0003129.pdf].
  5. Feb 13, 2017 #4


    Staff: Mentor

    Thread closed for moderation while the provided references are reviewed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook