Tag Archives: microwave

Gravity Makes Some Waves


Gravity, the movie, made some “waves” at the recent Academy Awards ceremony in Hollywood. But the real star in this case, is the real gravity that seems to hold all macroscopic things in the cosmos together. And the waves in the this case are real gravitational waves. A long-running experiment based at the South Pole has discerned a signal from the Cosmic Microwave Background that points to the existence of gravitational waves. This is a discovery of great significance, if upheld, and confirms the Inflationary Theory of our universe’s exponential expansion just after the Big Bang. Theorists who first proposed this remarkable hypothesis — Alan Guth (1979) and Andrei Linde (1981) — are probably popping some champagne right now.

From the New Statesman:

The announcement yesterday that scientists working on the BICEP2 experiment in Antarctica had detected evidence of “inflation” may not appear incredible, but it is. It appears to confirm longstanding hypotheses about the Big Bang and the earliest moments of our universe, and could open a new path to resolving some of physics’ most difficult mysteries.

Here’s the explainer. BICEP2, near the South Pole (where the sky is clearest of pollution), was scanning the visible universe for cosmic background radiation – that is, the fuzzy warmth left over from the Big Bang. It’s the oldest light in the universe, and as such our maps of it are our oldest glimpses of the young universe. Here’s a map created with data collected by the ESA’s Planck Surveyor probe last year:


What should be clear from this is that the universe is remarkably flat and regular – that is, there aren’t massive clumps of radiation in some areas and gaps in others. This doesn’t quite make intuitive sense.

If the Big Bang really was a chaotic event, with energy and matter being created and destroyed within tiny fractions of nanoseconds, then we would expect the net result to be a universe that’s similarly chaotic in its structure. Something happened to smooth everything out, and that something is inflation.

Inflation assumes that something must have happened to the rate of expansion of the universe, somewhere between 10-35 and 10-32 seconds after the Big Bang, to make it massively increase. It would mean that the size of the “lumps” would outpace the rate at which they appear in the cosmos, smoothing them out.

For an analogy, imagine if the Moon was suddenly stretched out to the size of the Sun. You’d see – just before it collapsed in on itself – that its rifts and craters had become, relative to its new size, made barely perceptible. Just like a sheet being pulled tightly on a bed, a chaotic structure becomes more uniform.

Inflation, first theorised by Alan Guth in 1979 and refined by Andrei Linde in 1981, became the best hypothesis to explain what we were observing in the universe. It also seemed to offer a way to better understand how dark energy drove the expansion of the Big Bang, and even possibly lead a way towards unifying quantum mechanics with general relativity. That is, if it was correct. And there have been plenty of theories which tied-up some loose ends only to come apart with further observation.

The key evidence needed to verify inflation would be in the form of gravitational waves – that is, ripples in spacetime. Such waves were a part of Einstein’s theory of general relativity, and in the 90s scientists observed some for the first time, but until now there’s never been any evidence of them from inside the cosmic background radiation.

BICEP2, though, has found that evidence, and with it scientists now have a crucial piece of fact that can falsify other theories about the early universe and potentially open up entirely new areas of investigation. This is why it’s being compared with the discovery of the Higgs Boson last year, as just as that particle was fundamental to our understanding of molecular physics, so to is inflation to our understanding of the wider universe.

Read the entire article here.

Video: Professor physicist Chao-Lin Kuo delivers news of results from his gravitational wave experiment. Professor Andrei Linde reacts to the discovery, March 17, 2014. Courtesy of Stanford University.

Pain Ray

We humans are capable of the most sublime creations, from soaring literary inventions to intensely moving music and gorgeous works of visual art. This stands in stark and paradoxical contrast to our range of inventions that enable efficient mass destruction, torture and death. The latest in this sad catalog of human tools of terror is the “pain ray”, otherwise known by its military euphemism as an Active Denial weapon. The good news is that it only delivers intense pain, rather than death. How inventive we humans really are — we should be so proud.


From the New Scientist:

THE pain, when it comes, is unbearable. At first it’s comparable to a hairdryer blast on the skin. But within a couple of seconds, most of the body surface feels roasted to an excruciating degree. Nobody has ever resisted it: the deep-rooted instinct to writhe and escape is too strong.

The source of this pain is an entirely new type of weapon, originally developed in secret by the US military – and now ready for use. It is a genuine pain ray, designed to subdue people in war zones, prisons and riots. Its name is Active Denial. In the last decade, no other non-lethal weapon has had as much research and testing, and some $120 million has already been spent on development in the US.

Many want to shelve this pain ray before it is fired for real but the argument is far from cut and dried. Active Denial’s supporters claim that its introduction will save lives: the chances of serious injury are tiny, they claim, and it causes less harm than tasers, rubber bullets or batons. It is a persuasive argument. Until, that is, you bring the dark side of human nature into the equation.

The idea for Active Denial can be traced back to research on the effects of radar on biological tissue. Since the 1940s, researchers have known that the microwave radiation produced by radar devices at certain frequencies could heat the skin of bystanders. But attempts to use such microwave energy as a non-lethal weapon only began in the late 1980s, in secret, at the Air Force Research Laboratory (AFRL) at Kirtland Air Force Base in Albuquerque, New Mexico.

The first question facing the AFRL researchers was whether microwaves could trigger pain without causing skin damage. Radiation equivalent to that used in oven microwaves, for example, was out of the question since it penetrates deep into objects, and causes cells to break down within seconds.

The AFRL team found that the key was to use millimetre waves, very-short-wavelength microwaves, with a frequency of about 95 gigahertz. By conducting tests on human volunteers, they discovered that these waves would penetrate only the outer 0.4 millimetres of skin, because they are absorbed by water in surface tissue. So long as the beam power was capped – keeping the energy per square centimetre of skin below a certain level – the tissue temperature would not exceed 55 °C, which is just below the threshold for damaging cells (Bioelectromagnetics, vol 18, p 403).

The sensation, however, was extremely painful, because the outer skin holds a type of pain receptor called thermal nociceptors. These respond rapidly to threats and trigger reflexive “repel” reactions when stimulated (see diagram).

To build a weapon, the next step was to produce a high-power beam capable of reaching hundreds of metres. At the time, it was possible to beam longer-wavelength microwaves over great distances – as with radar systems – but it was not feasible to use the same underlying technology to produce millimetre waves.

Working with the AFRL, the military contractor Raytheon Company, based in Waltham, Massachusetts, built a prototype with a key bit of hardware: a gyrotron, a device for amplifying millimetre microwaves. Gyrotrons generate a rotating ring of electrons, held in a magnetic field by powerful cryogenically cooled superconducting magnets. The frequency at which these electrons rotate matches the frequency of millimetre microwaves, causing a resonating effect. The souped-up millimetre waves then pass to an antenna, which fires the beam.

The first working prototype of the Active Denial weapon, dubbed “System 0”, was completed in 2000. At 7.5 tonnes, it was too big to be easily transported. A few years later, it was followed by mobile versions that could be carried on heavy vehicles.

Today’s Active Denial device, designed for military use, looks similar to a large, flat satellite dish mounted on a truck. The microwave beam it produces has a diameter of about 2 metres and can reach targets several hundred metres away. It fires in bursts of about 3 to 5 seconds.

Those who have been at the wrong end of the beam report that the pain is impossible to resist. “You might think you can withstand getting blasted. Your body disagrees quite strongly,” says Spencer Ackerman, a reporter for Wired magazine’s blog, Danger Room. He stood in the beam at an event arranged for the media last year. “One second my shoulder and upper chest were at a crisp, early-spring outdoor temperature on a Virginia field. Literally the next second, they felt like they were roasted, with what can be likened to a super-hot tingling feeling. The sensation causes your nerves to take control of your feeble consciousness, so it wasn’t like I thought getting out of the way of the beam was a good idea – I did what my body told me to do.” There’s also little chance of shielding yourself; the waves penetrate clothing.

Read the entire article here.

Related video courtesy of CBS 60 Minutes.