Surprising magnetic effect of light discovered at University of Michigan (2011) | Hacker News Reader

Surprising magnetic effect of light discovered at University of Michigan (2011)

michigantoday.umich.edu

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They goofed, see the comments on their paper (http://prl.aps.org/abstract/PRL/v98/i9/e093901).

namely

http://scholar.google.com/scholar?cluster=169089650815815794...

and

http://scholar.google.com/scholar?cluster=274756171832259655...

Prime example of why storing papers behind paywalls is a bad idea.

I can't read anything linked.

The authors then invoke Faraday's law H r E= i! 0 and conclude that the integral on the left side of Eq.(2) is identical to the first integral on the right. The theoretical result claimed in the Letter is directly predicated on this conclusion. This conclusion, however, is valid only ...

Continued?

where m (p) is the peak value of induced magnetic (electric) dipole moment and r (" r) is the ratio of magnetic (electric) permeability (permittivity) of the sphere and the surrounding medium at the given frequency. Equation (9) in [1] is a consequence of Eq.(8): JM º¿ 1= ...

The bottom of the second link (first Google Scholar link) leads to a free copy of the comment from Kent State University's website.

This rendered very oddly in Chrome on OS X: http://i.imgur.com/xFiNhav.png

PDF of first comment: http://muri.lci.kent.edu/Publications/Papers_KSU/PPM_PRL99_2...

The strange symbols appear because LaTeX use strange fonts with strange encodings, so the formulas look nice in the pdf but if you cut and paste them, and use a standard font to render the symbols then they are mapped to random characters in the standard fonts.

Those comments are scathing, they read like a post doc talking to an undergrad about their problem sheet!

"Equation (9) actually applies only to a perfectly conducting sphere and has been known for over 100 years..."

If an incorrect paper makes it into PRL, and someone is really sure, then there's blood in the water, and the sharks can be merciless.

I haven't read the papers, so I can't comment except to say that, just as Physics can let you be really right about something in nature, if you're not correct, sometimes you can be really wrong.

What parts are invalid? All, or just some?

I could only read one of the comments, and I wouldn't know enough physics to follow along, anyway.

Hardly surprising. Explanation here: http://www.youtube.com/watch?v=lpI6ikj1G-s

Does anyone know what happened with this? I googled "magnetic effects of light new type of solar cell" but I only got press from 2011 in the results.

The title of the paper is: Optically-induced charge separation and terahertz emission in unbiased dielectrics.

The news release is completely out-to-lunch (eg "Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored." Are you kidding? Light doesn't even propagate without the magnetic field) so I'd start by tracking citations of the original paper.

We know it's electromagnetic waves, but as it says we tend to ignore the latter part.

Having just studied for (and passed! yay me!) my amateur radio license exam, I've been mulling over this common omission of consideration of propagating magnetics. Phase too: we're so focused on frequency that we overlook phase. Polarization is also underrated, with a study last year suggesting "infinite bandwidth" (so said news reports) when used creatively.

Revisiting basics can reveal wonderous things.

If you take a look at how QAM works mathematically, it's getting such wonderful results because it's using two carriers with phase differences to do everything. It lets you do some really cool things depending on how well you can recover that phase.

They meant that they thought magnetic effects were weaker than electric in this particular situation, not in general. It's just worded horrendously in the press release.

Note that this from 2011. But it's still pretty cool when discoveries occur that weren't predicted by the models.

It must feel good to discover something 8 orders of magnitude stronger than predicted.

I emailed the author of the paper. Hope he gets back to us, this is cool.

"The light . . . must be focused to an intensity of 10 million watts per square centimeter. Sunlight isn't this intense on its own . . ."

Just a bit of an understatement.

Start with full-on solar intensity of 1000 watts per square meter. 100x100 meters gives the power input needed. Focus that on 1m^2, then focus that in turn to 1cm^2. Sounds doable.

It's not that simple. There's a minimum beam size, and passive optics won't let you alter that.

https://en.wikipedia.org/wiki/Gaussian_beam#Beam_width_or_sp...

at 10MWt/cm2 how long the exposure is before the material melts/evaporates?

so were problems found with the tech so it was abandoned or what? hard to know where it's going if anywhere with no followup...

Welcome to academia.

How does Michigan consistently have such crazy research going on?

It's typically in the top 3 public US colleges and top 20 overall. The average SAT score coming in is 1900 with over 25% of their freshman class arriving with 4.0 GPAs out of high school. So they have a pretty good program by typical measures.

Their advantage then over similar schools is the sheer size and funding. A school like Dartmouth probably has 'smarter' students enrolling on average, but Michigan's engineering college has more students (8,000+) than the entirety of Dartmouth (6,100). So take those 8,000 engineering students and add another 32,000 in the non-engineering tracks (many of whom are in sciences, medicine, mathematics, physics, etc.) and you're bound to produce some interesting research.

So a ton of smart students, but then there's the money... U of M has the 8th largest endowment ($8 billion) in the US and the 2nd largest research budget at over $1.2 billion per year. They spent $190mm on engineering research last year and over $550mm in the medical school on health / biotech R&D.

One could ask why they don't produce more than they do.

Realistically, the only things that matter that you mentioned are money (not the endowment, though, just the research budget, AKA grant money) and the facilities.

Undergrads are basically worthless (in fact, they may be a detriment because they drain resources from the professors and the grad students).

Does this mean tractor beams can be made real? :)

They can already be made real.

A) Make sure your ship is bigger

B) Shoot a ton of highly charged electron beams at the enemy space ship to ionize their hull

C) Magnetize your hull to the opposite charge and bring in the ship

How does one go about decelerating the other ship before it smashes into yours?

D) Magnetize your hull to the same charge and bring in the ship

The other ship would have momentum in the direction Of you. I suppose you could swap your hulls charge to repell

Change your ship's charge so that it's the same as the pulled ship, maybe?

this is 2 years old

Thank you for helping those of us unable to do basic arithmetic.

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