Sunday, February 18, 2007

"Resolving" Einstein's twin paradox

Because the hype about the bizarre physicists sold as "critics of string theory" has already faded away, many journalists must find something else, comparably or even more dumb, to write about, something that would satisfy their instincts to misinform their readers.

The following "story" is a good example showing how breathtakingly limited many journalists and their bosses are. An employee of LSU has posted the following press release on the LSU website:

Let me just copy the first paragraph here:

  • Subhash Kak, Delaune Distinguished Professor of Electrical and Computer Engineering at LSU, recently resolved the twin paradox, known as one of the most enduring puzzles of modern-day physics.

The press release is full of nonsensical comments about his "quantum" explanation based on "distant stars". It is not hard to see that the correct first paragraph should have been

  • Subhash Kak seems to be a canonical example of a new Einstein who can't understand special theory of relativity, not even at the high school level. Laymen often face problems when they try to digest how it is possible that a brother who's been moving quickly and returned from a long space trip will be younger: the age of the brothers will differ. But this conclusion is a fact that has been experimentally verified, and long before it was checked, it was presented as a well-established conclusion of the special theory of relativity in Einstein's paper of 1905. Einstein never considered any of these phenomena to be a paradox and other serious physicists didn't consider it a paradox either.

Every journalist who writes about the "twin paradox" should at least try to open the Wikipedia page about the twin paradox that explains quite clearly that there has never been any paradox. He should read at least one paragraph. Be sure that Wikipedia is reliable in more than 99% of similar cases, including this case in which the Wikipedia article is labeled as "needing attention of experts": in this sense, Wikipedia is a peer-reviewed source. There are hundreds of other sources that a casual journalist or Internet user may find to become sure that there has been no paradox to solve.

Twin paradox: in SR and GR

In special relativity, only the inertial observers are subjects to the same laws of physics. The guy who stays on Earth is approximately inertial, and he can correctly calculate that this brother will be younger because the wiggly time-like lines in Minkowski spacetimes are shorter than the straight lines. The laws for the other guy are more complicated.

The general theory of relativity allows us to use all reference frames, including the accelerated ones, but it is no longer true in general relativity that the "pace of time" is universal and only depends on the coordinate differences. Quite on the contrary, the "pace of time" in general relativity depends on the gravitational field - or the metric tensor, if you wish - and the two brothers simply see different gravitational fields which is compatible with the fact that their aging will be asymmetric.

Every smart 15-year old kid who is interested in physics should understand these things. There is no paradox, there has never been any paradox, there is no quantum mechanics needed to understand what happens because it has nothing to do with quantum mechanics, and it is unlikely that the Mach principle based on stars could be revived - and there is no reason for such a revival. We either use the special relativistic approximation or general relativity. In both cases, we arrive at the same conclusion unless we make errors.

Happiness in the media

Nevertheless, this LSU press release has been celebrated - see - by

  • Tech Blorge, Australia
  • Kashmir Newz, India
  • Daily News & Analysis, India
  • iTWire, Australia
  • CNN-IBN, India
  • Hindustan Times, India
  • Technocrat.Net, Massachusetts
  • Innovations Report, Germany
  • SpaceRef.Com
  • YubaNet, California
  • PhysOrg.COM, Virginia
  • EurekAlert, DC

They tell you that Kak has solved something that no one else, not even Einstein, could solve. You wonder whether these people actually believe that such a mad proclamation is likely: it certainly looks so. They want to believe it. Especially some of them want to believe it.

For example, you may see that Indian sources are over-represented. That's evidence that the journalists who belong to the same groups as the people who claim a "discovery" are much more likely to believe that the announced "discovery" is meaningful. To make the story even more impressive, the CNN-IBN story in India is rated by the readers. The average rating from 75 users is 9.5 stars: the maximum is ten stars. Well, this shows that about 95% of their Indian readers are complete ignorants about high school physics.

I assure the people in India who know what the "twin paradox" is and what it's not - for example high-energy physicists ;-) - that if they're gonna ignore these trends instead of trying to patiently explain the people around how science works, India may simply return to the trees.

And that's the memo.

Young Earth

A bonus: in order to show how educated, self-consistent, and brilliant the Earth scientists are, let me congratulate to Marcus Ross. He was just awarded a PhD: see Vancouver Sun. Marcus Ross believes that the Earth is as young as 10,000 years and his PhD thesis is about marine reptiles that disappeared 65 million years ago.

What do I think about it? I have not read the thesis but I have no reason to doubt the comments by his advisors that it's a good thesis. If it's a good thesis and if he satisfied other rules, he should be given a PhD. But unlike others, I don't think that having a PhD means that other scientists must take the person seriously, and I will personally continue to consider the Young Earth creationists to be nutcases.


  1. Dear Luboš:

    Hi. I'm an Indian chemical engineer, with a very minimal knowledge of theoretical physics, but had absolutely no trouble understanding Kak's paper (with all its flaws!) and concluding that it was nonsense that somehow got through peer review.

    However, I had a very difficult time convincing some of my friends who believed that Kak might have achieved a breakthrough, and that I am not able to understand it since theoretical physics is not my field.

    So, thanks for posting a blog entry on this! I've pointed your blog entry to these friends, and hopefully that (plus your reputation) will silence them!

    Of course the fact that the Indian media is trying to popularize this is very, very sad. Even The Times of India, which I had respect for, has published this story (
    - at least for consolation, 'solved' is in quotes, and it mentions that Kak claims to have solved the paradox.

    With best wishes,
    Ganesh Sriram
    Los Angeles

  2. The press release does indeed immediately expose this as ignorant nonsense; but if people really want to give Subhash Kak a fair shake, they can also read the whole paper. It is in the (unreviewed) arxiv archive, at The paper as it appears in the journal IJTP is the same, with only formatting changes. (I have both.) There you can confirm that it is truly ignorant nonsense, just as the press release would lead anyone with a reasonable basic level of education in physics to think.

    I'm pretty confident that Kak wrote the press release.

    It gets worse.

    As well as being drivel, Kak's paper turns out to be unoriginal drivel. It is a crude recycle of the "cosmic relativity" previously written up by Indian relativity crank C. S. Unnikrishnan – who actually is a physicist; though not any better at relativity. The commonalities do not amount to a direct copy; but by normal standards of scholarship Kak's acknowledgement is grossly inadequate. The only bit that is new in Kak's paper is that he uses a grossly inferior way of detecting the "cosmic rest frame" in terms of velocity distributions, whereas Unnikrishnan uses the CMBR anisotropy.

    Kak does cite a different paper by Unnikrishnan, but only as justification for the claim that all the well established prior work on the twin paradox is wrong. Kak fails to credit Unnikrishnan's role in the new resolution of the paradox that is proposed.

    Here's the paper trail.

    (1) Unnikrishnan, in 2004, wrote "Cosmic Relativity: The Fundamental Theory of Relativity, its Implications, and Experimental Tests", which can be found in the arxiv archive at This error-riddled drek proposes that "all relativistic effects that are presently attributed to kinematics of relative motion in flat space-time are in fact gravitational effects of the nearly homogeneous and isotropic Universe. The correct theory of relativity is the one with a preferred cosmic rest frame."

    (2) Unnikrishnan, in 2005, wrote "On Einstein’s resolution of the twin clock paradox", in which he claims that Einstein's own explanations are full of errors. In this paper, Unnikrishnan also describes briefly his proposed solution with reference to the frame in which the CMBR is isotropic, and cites the 2004 paper.

    (3) Kak, in 2007, publishes the paper that is the subject of this blog. He cites the 2005 paper in support of the idea that prior resolutions of the "paradox" are in error; but fails to make any mention of the close similarity between his proposed solution and that given by Unnikrishnan in 2004.

    The actual "resolution" is a wholly unoriginal calculation of time delays in the frame of the twin at rest. The errors are sophormoric arguments for a necessary association with an isotropic universe; and flatly erroneous dismissal of prior work as "inadequate" or "not in consonance".

    Cranks are a perennial feature of physics. It's not just Indians; we find them in every corner of the globe. There's no reasoning with them; but there is a need to give a clarification for the rest of us. The most incomprehensible feature of this fiasco is that Kak's paper ever got past a basic peer review.

    Minor addendum… the Louisiana State University has, as far as I can tell, a first rate research group in relativistic physics. I'm sure it never even occurred to Kak that he could have benefited from talking to them before hiving off into a field where he has no background.

    Cheers – Chris Ho-Stuart

  3. Any transformation between two observers is a space-time dialogue between two entities A and B about a third entity C. In the 'Galileo Transformation', the third entity C is understood, does not appear in the notation. But the 'Lorentz Transformation' completely ignores the entity C, and this is why the twin paradox.
    I would like to introduce some new transformations that preserve the local velocity of light. Also resolve the twin paradox.
    Relational Transformation:

  4. I have to disagree with you here Lubos. The Wikipedia article on the twin paradox is terrible! I got almost nothing out of it. It seems to be generally under attack by crackpots. Check out the 13+ archives on the Talk page! I'm pretty bad at physics, but I disagree with you also on the explanation of the paradox. You don't have to mention gravity or accelerating frames to explain it, do you? Isn't it just length contraction? The guy flying past the Earth in a spaceship thinks the distance to a nearby star (call the distance D1) as less than the distance we think it is here on Earth (call it D2). If his speed past us is S, we know we will have aged D2/S when he gets to the star, while he will have aged only D1/S.

  5. Dear Steve, I wrote this article 5.5 years ago. So it's common sense that in that time, an article at Wikipedia could have changed, right? I am not going to update all my propositions about twin paradox and millions of other articles on Wikipedia and thousands of other websites.

    Nevertheless, this article still looks fine to me. I don't understand your problems with that. The twin paradox may be explained in special relativity, without gravity, where at most one system among the two is inertial. The article does it. It may also be explained in general relativity where all reference frames are possible and then age difference is a result of different gravitational fields around both trajectories.

    On the other hand, your comments make no sense to me. Various effects in special relativity are related in various ways - after all, it's one theory, special relativity - but twin paradox is not "just length contractions". The twin paradox is a result of "time dilation" which is an effect treated as independent of "length contraction". Of course that one may related them by various arguments but your comments don't do it, they just add lots of confusion about it.

  6. SteveBrooklineMASep 26, 2012, 9:12:00 PM

    Hey Lubos- You're right, of course, Wikipedia may have changed over the years. It does seem to attract a lot of nonsense though, as reflected in the numerous battles in the talk sections. The (non)-paradox exists even if both twins are in inertial frames. That's why I think adding non-inertial factors complicates things where there is no need. I'm measuring aging by time: distance divided by speed = time. Although the speed of the passing rocket as seen by the earth twin is the same as the speed of the receding earth as seen by the rocket twin, the distance to the star differs for the two. The part of the Wikipedia article I think
    is good is