All That Matters

Metamaterials are very exciting structures, one of the most exciting areas in photonics, I think. That’s because they allow an almost arbitrary modification of light (or acoustic) waves propagating through the material. Sadly, however, the highly promising potential of metamaterials gets often completely overblown by news reporting on fantastic effects. Cloaking devices are the prime example. Here I try to come up with a few points that might help to sort science from fiction.

Metamaterials are small metallic structures, typically rings or wires, that locally change the materials properties. These structures are much smaller than the wavelength of light. To a light wave, it is as if the structure is not made of tiny rings and wires, but looks like a homogeneous material. Hence their name ‘metamaterials’. Meta is Greek and means beyond. The first metamaterials all used the same small units of wires and rings, repeated over and over. With this, you can achieve a negative index of refraction, which enables superlenses – lenses with perfect resolution.

The original metamaterial designs consisted of electromagnetic resonators made of rings and wires. These devices are for THz and GHz radiofrequencies. Credit: NASA, via wikimedia

The next key advance was that metamaterials needn’t only consist of uniform assemblies of rings and wires. If you change the properties of each unit of a metamaterial, you can create a material that to light looks as if it changes its properties. This way it is possible to modify the propagation of light as it goes through the metamaterial. You can make it go round corners, turn it around. In theory, the possibilities are nearly endless, that much is clear.

The prime example to demonstrate the possibilities of metamaterials is the optical cloak. The term is borrowed from the science fiction series Star Trek. And naturally, it is these kind of visions that let our fantasy go wild when thinking about metamaterials cloaking. Images of Star Trek, or ‘Harry Potter cloaks’ and the ‘invisible man’ are often conjured when journalists, university press offices and even scientists try to explain metamaterials to the public. Sadly, in relation to what metamaterials can do, this is nonsense.

So here are a few things that metamaterials can and cannot do.

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As an editor of a scientific journal, one of my key duties is to organise the peer review of submitted scientific papers. There, I ask other experts to take a look at a paper and let me know their opinion on technical correctness of their findings, and perhaps also what the importance and impact of a paper could be. The reviewers are aware of the identity of the authors, whereas the identity of the reviewers is not revealed to the authors.

The requirement to use peer review is not set in stone, but it has proven a very useful tool to assess a scientific paper. However, given the huge amount of work involved where scientists review each other’s work. Indeed, a lot has been said about the peer review process, whether it should be opened, or completely abolished etc. Here I just like to focus on the issue of transparency, which has been subject of a commentary by Bernd Pulverer from the European Molecular Biology Organization in last week’s issue of Nature. Access is free.

Historically, peer review as such is known for a long time, but is only systematically been used since around the mid-20th century. Certainly the very idea of peer review has been a new concept to Albert Einstein, when following peer review his paper on gravitational waves was rejected by Physical Review in 1936:

Dear Sir,

We (Mr. Rosen and I) had sent you our manuscript for publication and had not authorized you to show it to specialists before it is printed. I see no reason to address the — in any case erroneous — comments of your anonymous expert. On the basis of this incident I prefer to publish the paper elsewhere.

Respectfully,
Albert Einstein

And even later on, peer review has not necessarily always been done. The famous 1953 Nature paper by Watson and Crick on the structure of DNA has not been peer reviewed. Competition was very tough in this case, and as John Maddox, former editor of Nature, allegedly said:

The Watson and Crick paper was not peer-reviewed by Nature… the paper could not have been refereed: its correctness is self-evident. No referee working in the field … could have kept his mouth shut once he saw the structure

Clearly, peer review was not always considered necessary by scientists as well as publishers. To me, it remains essential. But I think the system could improve, and one area where this could be done with ease is its transparency. At the moment, the process is not fully transparent, neither to authors nor to scientists other than the reviewers. As it stands, there is a lot of implicit trust in the work of journal editors…

More transparency!

Bernd Pulverer’s commentary describes an effort to increase transparency at The EMBO journal. Since 2009, the journal has been running a trial where in case of publication the anonymized referee reports sent to authors, the editorial decision letters as well as the author’s rebuttals to reviewers are published as a supplementary file along with the paper. (disclaimer: Nature Publishing Group publishes this journal on behalf of EMBO).

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