# Is gravitational lensing a good way to search for negative mass?

Is it possible to verify negative mass with gravitational lensing? The following video proposes an idea that galaxies are surrounded by negative mass: https://youtu.be/MZtS7cBMIc4

Could this be proven or disproven by looking at gravitational lensing of distant galaxies, by looking at Hubble Deep Field images? I would expect if negative mass surrounded a galaxy, it should cause the opposite effect of the positive mass galaxy. If there is surrounding negative mass, there should be an “anti” lensing effect just outside the normal lensing effect. Could someone perform this analysis and confirm or deny that idea?

Edit: In the following image, and others, I have looked to see if I could see such an effect out further from the source visually, and it is hard to tell. There are so many galaxies in front that aren't affected by the lensing. It might take a computer analysis of images surrounding the "ring" effect to see if there is a "radial effect" around the ring. Most images probably don't show enough of the surrounding area to where the radial effect as predicted in the paper Izumi et al. (2013) would be apparent. If this is present, I would think it indicates negative mass surrounding the positive mass, and would be a huge discovery confirming negative mass! If absent, it would likely show that there is at least not a significant amount of negative mass clustered around the galaxies (wouldn't be a total disproof of negative mass).

Image from: Galaxies - Gravitational Lensing

• Did you come from the Action Lab video? Jokes aside, fringe youtube videos rarely represent the state of the art in science. Negative masses are not predicted or admitted by any physical theory I know of. That's different for imaginary masses, whose tachyons are admitted by GR, but violate other physics. Feb 22 '19 at 15:01
• @CarlWitthoft Afaik GR can describe negative mass: "All of these are violations of one or another variant of the positive energy condition of Einstein's general theory of relativity; however, the positive energy condition is not a required condition for the mathematical consistency of the theory." Thus, the positive energy condition is simply a postulate in the GR and its math would work even without it. Feb 22 '19 at 17:13
• @peterh: Many things are possible in consistent theories, which then disagree with observations. Feb 22 '19 at 19:40
• @AtmosphericPrisonEscape It is true, but non sequitur. If negative mass would exist, and it would behave as the GR math describes it, and there would be enough negative mass in the Universe to detect it, then we could find it with gravitational lensing. Btw, I am not sure, but AFAIK the dark energy behaves like a roughly constantly distributed, negative mass permeating the whole Universe. Feb 23 '19 at 20:17
• Whoever voted to close this question because it's about Earth Science needs to explain how gravitational lensing and negative mass are Earth Science matters. Or perhaps a moderator needs to investigate the frivolous or incompetent use of VTC's... Feb 25 '19 at 23:31

This was discussed in a recent paper by an Oxford cosmologist: https://arxiv.org/abs/1712.07962

It claims that there have already been some detections of negative mass using gravitational lensing:

In fact, “puzzling results” in clusters such as negative masses have been discussed in the literature (Andreon, Punzi, & Grado 2005). For example, Chandra observations of the merging cluster Abell 2034 found hints of a negative mass and therefore did not plot those data (Kempner, Sarazin, & Markevitch 2003), regions of the mass profile in the galaxy NGC 4636 yielded “unphysical” negative masses (Johnson et al. 2009), in the NGC 3411 galaxy group the total mass was found to decline with increasing radius – requiring material with negative mass (O’Sullivan et al. 2007), measurements of galaxy clusters using the Sloan Digital Sky Survey yielded data that indicate a negative mass in poor clusters with fewer than five galaxies (Hansen et al. 2005), a CMB cluster lensing study found a cluster with “a fairly significant preference for negative mass” (Baxter et al. 2017), and a number of strong and weak gravitational lensing studies have discussed or found indications of negative masses in reconstructed mass distributions (Evans & Witt 2003; Clowe, Gonzalez, & Markevitch 2004; Clowe et al. 2006; Liesenborgs, De Rijcke, & Dejonghe 2006; Diego et al. 2007).

• Some criticism of the referenced paper can be found at arxiv.org/abs/1902.08287
– user24157
Mar 7 '19 at 20:28

One reference I found on this subject was Izumi et al. (2013), who note that the images produced by lensing around a negative mass are radially distorted while lensing by a positive mass are tangentially distorted, and that this effect can be distinguished without prior knowledge of the lens position by measuring the alignment of lens images.

I am not an expert in general relativity so I'm not able to evaluate their results, but assuming the paper is correct it does look like negative mass could indeed be detected by observations of gravitational lensing. The question of whether negative mass exists is another matter, so far it doesn't look like a likely prospect.

• I wonder, do we know if anyone has done a search using this idea? It would probably be a huge discovery if negative mass were actually found! Mar 2 '19 at 1:45
• @Jonathan - probably not, most of the discussion is theoretical (and also includes things like lensing by wormholes). Observations of gravitational lensing do take place but so far nothing has turned up that would require negative mass to explain the observations. There are various reasons we wouldn't expect negative mass to exist but that's a whole different question (and probably fits better with physics rather than astronomy).
– user24157
Mar 2 '19 at 18:02
• The end of the paper reads "It would be interesting to investigate numerically light propagation through realistic voids in cosmological simulations, because the present model obeys a simple power-law. It is left for future work." This is intriguing!
– uhoh
Sep 22 '20 at 0:52

If the negative mass is not inside but outside the positive mass, wouldn't it push light passing by away from it, thus towards the positive mass, which would lead to a perceived higher gravitational lensing effect on the positive mass? If so, then https://www.spacetelescope.org/news/heic2016/ could maybe partially explained by negative mass halos on those galaxies. Villata apparently has mentioned such a "antigravitational lensing effect". Conceptually it feels much more natural than most dark matter theories.

• I did not read the link, but dark matter gravitates. Dark energy behaves like an antigravitating thing. Oct 22 '20 at 22:40
• Wow, negative mass attracts negative mass, positive mass attracts positive mass, but negative mass distracts positive. The result might be as in the source. It is very interesting. Oct 23 '20 at 9:16
• I would think negative mass would do the opposite gravitational lensing of what regular mass does - e.g. act like a concave vs. convex lens. I also speculate negative mass would repel all things, including itself, so it would generally be spread very thin. Since positive mass attracts, it is possible the sparse negative mass might gather near positive mass. Nov 3 '20 at 2:26