Sign up ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

The question concerns this video:

It says that the Gravitational Lens effect is an illusion, meaning it's not caused by gravity but by change in density of a plasma atmosphere. It claims further that this gravitational lens effect is not present with other massive objects that aren't made of, or surrounded by, plasma.

Does this mean general relativity is invalid, somewhat invalid, or still luckily valid? What is the merit of claim that bending could be caused by plasma and not by gravity?

share|cite|improve this question
I think my answer to this question adequately summarizes an effective answer – Jim Jun 27 '14 at 18:35
that question is very different..and answer just says no to it!?!?! am i missing something – Muhammad Umer Jun 27 '14 at 18:49
nope. That style answer is mostly applicable here. The answer is a simple no. There are some well written deeper reasons below, but in this case, my answer would be "no. Don't believe everything you hear". Gravitational lensing is real and massively evidenced. If there was a snowball's chance in hell what this guy said was true, it would have been in headlines and on primetime news – Jim Jun 27 '14 at 18:57
again..i understand what you are saying but at this point your 'no' is just as credible...not saying you are wrong..just saying i can't just accept 'no' because 'trust me'. – Muhammad Umer Jun 27 '14 at 19:59
A valid point. I do not hope you accept a no based on what I have said. I only hope it causes you to not accept a yes. – Jim Jun 30 '14 at 13:24

4 Answers 4

up vote 4 down vote accepted

Is it true that gravitational lensing only occurs for objects made of plasma?

Most of space contains a plasma, or at least some ionisation, at some density or other, making the claim hard to dispute at that level. Also, gases and/or plasmas will tend to exist with higher densities in deeper gravity wells.

What is the merit of claim that bending could be caused by plasma and not by gravity?

In general it is possible for light paths to be changed by interaction with matter (a glass lens being an obvious example). In principle similar distortion could happen with a rarefied plasma over large distances. A density variation at the right scale, and with a simple shape would be required.

I expect however that the claim in the link is just a conjecture/challenge, and not mathematically or scientifically robust (although I don't personally have the knowledge and skills to assess that). I suspect that the lensing seen in an Einstein ring would be very hard to duplicate using realistic values for plasma density near the lensing object.

To me, there are plenty of warning signs that this is a crackpot claim from the link. Unfortunately the world is full of them. Often such people cannot be corrected by scientific evidence, in fact they will self-promote that there is "controversy" when engaged in conversation, or complain of being "suppressed by the establishment" when ignored. I am not saying those thing apply to the author (I have not checked other publications), but I would be wary of the "a NASA physicist" label - it is likely correct on some technical label (he worked for NASA and has a qualification in physics) but is not particularly meaningful.

It doesn't help the lay audience (NB I include myself here) when real scientific controversies and useful scepticism can follow a similar pattern. Popular proponents of badly-thought-through or outlier theories often manage to pick up on the form of this and produce "science-y" work, making it harder to filter out good from bad.

Update: I have struggled through a few pages of and stand by this - the work appears to be random picking of equations plus handwaving arguments about how they connect. Nothing is properly analysed.

Does this mean general relativity is invalid?

No, even if somehow the claim had merit, there is plenty of evidence for GR outside of gravitational lensing.

For example: Time-dilation effects of general relativity can be measured directly by atomic clocks. They have got so accurate that we can actually measure the time dilation of a few metres height difference at ground level. The GPS system needs to account for this effect.


It is well known that General Relativity and the Standard Model of quantum mechanics, although our best current models in physics, cannot be the last word. They are not compatible, and where they overlap (typically when considering cosmology or black holes) there is a need for a combined or replacement theory. That doesn't make the theories "wrong" any more than Newtonian physics was "wrong", but it does mean we can expect some extensions or a deeper theory to emerge at some point.

share|cite|improve this answer

Did you notice the title of the video?

Former NASA Physicist Disputes Einstein’s Relativity Theory

At the moment main stream physics, which is what we discuss here, does not accept all the various theories trying to unseat General Relativity . Usually these people have an obsession with Einstein or other prominent physicist as personalities . Look at the humorous crackpot index .

On the subject, the lensing has been established from images of galaxies lensed by clusters of galaxies. Plasma is a phenomenon around hot stars and have nothing to do with observations ( except that in trying to measure the gravitational lensing by the sun would need carefully taken care of).

Sorry to say it does not sound a serious proposal.

share|cite|improve this answer
No need to be all apologetic, it's not personal to me one way or another. I would like to know if you are saying that his claim " that a phenomenon known as gravitational lensing does not take place as described by relativity theory" is invalid. And can you provide source for that this forum is only for mainstream physics, what is mainstream?..Also i didn't get what you meant by notice the title? What are you implying? – Muhammad Umer Jun 17 '14 at 4:20
People who come out using "disputing Einstein" have a chip on their shoulder. If you have a good alternate theory you should dispute general relativity, not the long dead Einstein. I am saying that plasma is not around galaxies and clusters of galaxies. It is hot matter ejected by stars as the sun. The sun experiment has not even been run yet. The data we have are from galaxies. – anna v Jun 17 '14 at 5:18
The author is clearly arguing that general relativity is wrong because supposedly major and only type of evidence has alternative explanation. He no where said einstien had mental issues or anything like that. – Muhammad Umer Jun 17 '14 at 5:49
+1 for the crackpot index itself. However, if you retain that string ''... which is what we discuss here'', don't you think you are bound to have people falling prey to item no. 28 in that index? Reverse psychology, is it? :) – The Dark Side Jun 17 '14 at 5:51
I am not talking about einstein having mental issues. It is the person who wants to get better than Einstein who has mental issues. As to his argument, plasma is not existing in the large distances between galaxies and clusters of galaxies so his proposal that that is what makes lensing is wrong. it is not a mainstream interpretation of the data from astrophysics. There are alternative cosmolgogies,, but the majority of the astrophysics community does not adopt it. – anna v Jun 17 '14 at 6:01

While it's a redshift rather than an angular deflection, the Pound-Rebka experiment confirming the interaction between light and gravity did not involve any plasma anywhere.

You could presumably repeat the experiment using photons directed at an angle, rather than upwards, though the angular deflection would be so small it only be possible to infer.

share|cite|improve this answer
maybe i don't understand the video and his claim correctly what is he disputing then? If Pound-Rebka Experiment proves him wrong. – Muhammad Umer Jun 17 '14 at 4:02
I must confess to having debunked the claim without watching the video. Also noteworthy is that plasma is a phenomenon of high temperature or of low pressure; the interplanetary, interstellar, and intergalactic media are all plasmas, just because they are so rarefied that any free electrons and ions are unlikely ever to find each other. – rob Jun 17 '14 at 7:35

Yes, it would be silly of us to imagine that those huge halos of plasma of up to twice the mass of the galaxy itself discovered in 2012, surrounding every galaxy, might have something to do with it. As it would be silly to assume plasma has nothing to do with redshift.

The simple fact is that plasma does not behave like solids, liquids or gasses. So to assume that a universe 99% plasma would behave like solids, liquids and gasses would be in error. One can not use the kinematics of ordinary gasses to describe a plasma state, yet this is precisely what is being done when one talks of it as being dust and gas that they observe in space. Such thinking leads to errors.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.