Let me summarize my thoughts about topics in theoretical physics:

  • Theory of everything: The theory of everything aims to unite all the four forces of nature into one single elegant equation.
  • Supersymmetry: important as, roughly put, it explains the nature of force in terms of matter.
  • The gravitino is the supersymmetric partner of graviton, which is a hypothetical particle that mediates the gravitational force.
  • Dark matter candidate: It is theorized that the graviton has no mass and on the other hand gravitino is very massive. Hence some nerds proposed dark matter may be made mainly of gravitinos.
  • Existence of gravitinos: It is suspected that early in the formation of Universe when it was still mostly in a plasma state, gluons (the force carrier of strong nuclear force) collided with each other and produced gravitinos.

My questions are:

  1. Is there any reliable, direct or indirect, method to detect gravitinos?
  2. If gravitinos were observed, would it mean that supersymmetry was the theory of everything?
  • 1
    $\begingroup$ SUSY is not a theory of everything in anyone's book. (In 2015, that is.) $\endgroup$
    – Ryan Unger
    Apr 10 '15 at 10:33
  • $\begingroup$ @0celo7 My apology I must have misunderstood super-symmetry thinking it is a promising candidate for grand unified theory but now it is only a feature in string theory. $\endgroup$
    – user6760
    Apr 10 '15 at 11:23

The answer to the first question is no. It is a basic but subtle point...

Science is about adopting the simplest explanation of phenomena. This is usually referred to as Ocam's razor. With very exotic, high-energy theories like string theory or here a gravitino (I think you have a typo!) there is no single clear signature that can not be explained by some other model in a modern experiment. Future experiments are a different game.

The reason being that the energy scales where these phenomena occur are so far from what we may probe experimentally that many different models look the same at these low energies. This is similar to how the modern atom and the older plum-pudding model look the same at lower energies with blunt experimental techniques used in the past. Many theories of physics reduce to older models with low energy experiments. For example at low energy relativistic effects die away and Newtonian physics becomes accurate. Indeed gravitinos predict measurable things for modern experiments that may be explained in many ways. We can not probe the scale where all the different theories make different predictions.

If gravitinos were observed supersymmetry would not be the theory of everything. Supersymmetry is not a theory, it is a symmetry a theory may have. Discovering a gravitino would indicate supersymmetry is a symmetry of nature lending significant proof towards a string theory as the theory of everything.

  • $\begingroup$ I can't edit to add a single letter, so could you please correct "Ocam's"? $\endgroup$ Jun 13 '15 at 13:54
  • $\begingroup$ -1: i) preamble about philosophy of science/Occam's razor is contentious. ii) your answer suggests that gravitinos could be detected i.e. there are detectable phenomena associated with gravitinos. distinguishing rival explanations is indeed another matter though. $\endgroup$
    – innisfree
    Jun 13 '15 at 14:41

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