Physics Archives

April 15, 2016April 15, 2016 by Evan Gough

A Super-Fast Star System Shrugs Its Shoulders At Physics

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

Astronomers have found a pair of stellar oddballs out in the edges of our galaxy. The stars in question are a binary pair, and the two companions are moving much faster than anything should be in that part of the galaxy. The discovery was reported in a paper on April 11, 2016, in the Astrophysical Journal Letters.

The binary system is called PB3877, and at 18,000 light years away from us, it’s not exactly in our neighborhood. It’s out past the Scutum-Centaurus Arm, past the Perseus Arm, and even the Outer Arm, in an area called the galactic halo. This binary star also has the high metallicity of younger stars, rather than the low metallicity of the older stars that populate the outer reaches. So PB3877 is a puzzle, that’s for sure.

PB3877 is what’s called a Hyper-Velocity Star (HVS), or rogue star, and though astronomers have found other HVS’s, more than 20 of them in fact, this is the first binary one found. The pair consists of a hot sub-dwarf primary star that’s over five times hotter than the Sun, and a cooler companion star that’s about 1,000 degrees cooler than the Sun.

Hyper-Velocity stars are fast, and can reach speeds of up to 1,198 km. per second, (2.7 million miles per hour,) maybe faster. At that speed, they could cross the distance from the Earth to the Moon in about 5 minutes. But what’s puzzling about this binary star is not just its speed, and its binary nature, but its location.

Hyper-Velocity stars themselves are rare, but PB3877 is even more rare for its location. Typically, hyper velocity stars need to be near enough to the massive black hole at the center of a galaxy to reach their incredible speeds. A star can be drawn toward the black hole, accelerated by the unrelenting pull of the hole, then sling-shotted on its way out of the galaxy. This is the same action that spacecraft can use when they gain a gravity assist by travelling close to a planet.

This video shows how stars can accelerate when their orbit takes them close to the super-massive black holes at the center of the Milky Way.

But the trajectory of PB3877 shows astronomers that it could not have originated near the center of the galaxy. And if it had been ejected by a close encounter with the black hole, how could it have survived with its binary nature intact? Surely the massive pull of the black hole would have destroyed the binary relationship between the two stars in PB3877. Something else has accelerated it to such a high speed, and astronomers want to know what, exactly, did that, and how it kept its binary nature.

Barring a close encounter with the super-massive black hole at the center of the Milky Way, there are a couple other ways that PB3877 could have been accelerated to such a high velocity.

One such way is a stellar interaction or collision. If two stars were travelling at the right vectors, a collision between them could impart energy to one of them and propel it to hyper-velocity. Think of two pool balls on a pool table.

Another possibility is a supernova explosion. It’s possible for one of the stars in a binary pair to go supernova, and eject it’s companion at hyper-velocity speeds. But in these cases, either stellar collision or supernova, things would have to work out just right. And neither possibility explains how a wide-binary system like this could stay intact.

Fraser Cain sheds more light on Hyper-Velocity Stars, or Rogue Stars, in this video.

There is another possibility, and it involves Dark Matter. Dark Matter seems to lurk on the edge of any discussion around something unexplained, and this is a case in point. The researchers think that there could be a massive cocoon or halo of Dark Matter around the binary pair, which is keeping their binary relationship intact.

As for where the binary star PB3788 came from, as they say in the conclusion of their paper, “We conclude that the binary either formed in the halo or was accreted from the tidal debris of a dwarf galaxy by the Milky Way.” And though the source of this star’s formation is an intriguing question, and researchers plan follow up study to verify the supernova ejection possibility, its possible relationship with Dark Matter is also intriguing.

February 14, 2016March 18, 2016 by Matt Williams

Chinese Fusion Test Reportedly Reaches New Milestone

Researchers at the Experimental Advanced Superconducting Tokamak facility in China have achieved a new milestone in fusion power. Credit: ipp.cas.cn

Fusion power has long been considered to be the holy grail of alternative energy. Clean, abundant power, created through a self-sustaining process where atomic nuclei are fused at extremely high temperatures. Achieving this has been the goal of atomic researchers and physicists for over half a century, but progress has been slow. While the science behind fusion power is solid, the process has not exactly been practical.

In short, fusion can only be considered a viable form of power if the amount of energy used to initiate the reaction is less than the energy produced. Luckily, in recent years, a number of positive steps have been taken towards this goal. The latest comes from China, where researchers at the Experimental Advanced Superconducting Tokamak (EAST) recently report that they have achieved a fusion milestone.

Continue reading “Chinese Fusion Test Reportedly Reaches New Milestone”

February 11, 2016March 18, 2016 by Evan Gough

Gravitational Waves Discovered: A New Window on the Universe

An illustration of Markarian 231, a binary black hole 1.3 billion light years from Earth. Their collision generated the first gravitational waves we've ever detected. Image: NASA

“Ladies and Gentlemen, we have detected gravitational waves. We did it.”

With those words, Dave Reitze, executive director of the U.S.-based Laser Interferometry Gravitational-Wave Observatory (LIGO), has opened a new window into the universe, and ushered in a new era in space science.

Predicted over 100 years ago by Albert Einstein, gravitational waves are ripples in space-time. They travel in waves, like light does, but they aren’t radiation. They are actual perturbations in the fabric of space-time itself. The ones detected by LIGO, after over ten years of “listening”, came from a binary system of black holes over 1.3 billion light years away, called Markarian 231.

The two black holes, each 30 times as massive as the Sun, orbited each other, then spiralled together, ultimately colliding and merging together. The collision sent gravitational waves rippling through space time.

LIGO, which is actually two separate facilities separated by over 3,000 km, is a finely tuned system of lasers and sensors that can detect these tiny ripples in space-time. LIGO is so sensitive that it can detect ripples 10,000 times smaller than a proton, in laser beams 4 kilometres long.

The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO

Light is—or has been up until now—the only way to study objects in the universe. This includes everything from the Moon, all the way out to the most distant objects ever observed. Astronomers and astrophysicists use observatories that can see in not only visible light, but in all other parts of the electromagnetic spectrum, to study objects in the universe. And we’ve learned an awful lot. But things will change with this announcement.

“I think we’re opening a window on the universe,” Dave Reitze said.

Another member of the team that made this discovery, astrophysicist Szabolcs Marka from Columbia University, said, “Until this moment we had our eyes on the sky and we couldn’t hear the music.”

Gravitational waves are a new way to study notoriously difficult things to observe like black holes and neutron stars. Black holes emit no light at all, and their characteristics and properties are inferred from cause and effect relationships with objects near them. But the detection of gravitational waves holds the promise of answering questions about black holes, neutron stars, and even the early days of our universe, including the Big Bang.

It’s almost impossible to overstate the magnitude of this discovery. Once we understand how to better detect and observe gravitational waves, we may come to a whole new understanding of the universe, and we may look back on this day as truly ground-breaking and revolutionary.

And it all started 100 years ago with Albert Einstein’s prediction.

For a better understanding of Gravitational Waves, their sources, and their detection, check out Markus Possel’s excellent series of articles:

Gravitational Waves and How They Distort Space

Gravitational Wave Detectors and How They Work

Sources of Gravitational Waves: The Most Violent Events in the Universe

February 10, 2016February 11, 2016 by Markus Pössel

Gravitational Wave Detectors: How They Work

It’s official: this Thursday, February 11, at 10:30 EST, there will be parallel press conferences at the National Press Club in Washington, D.C., in Hannover, Germany, and near Pisa in Italy. Not officially confirmed, but highly probable, is that people running the LIGO gravitational wave detectors will announce the first direct detection of a gravitational wave. The first direct detection of minute distortions of spacetime, travelling at the speed of light, first postulated by Albert Einstein almost exactly 100 years ago. Nobel prize time.

Time to brush up on your gravitational wave basics, if you haven’t done so! In Gravitational waves and how they distort space, I had a look at what gravitational waves do. Now, on to the next step: How can we measure what they do? How do gravitational wave detectors such as LIGO work?

Recall that this is how a gravitational wave will change the distances between particles, floating freely in a circular formation in empty space: The wave is moving at right angles to the screen, towards you. I’ve greatly exaggerated the distance changes. For a realistic wave, even the giant distance between the Earth and the Sun would only change by a fraction of the diameter of a hydrogen atom. Tiny changes indeed.

How to detect something like this?

The first unsuccessful attempts to detect gravitational waves in the 1960s tried to measure how they make aluminum cylinders ring like a very soft bell. (Tragic story; Joe Weber [1919-2000], the pioneering physicist behind this, was sure he had detected gravitational waves in this way; after thorough analysis and replication attempts, community consensus emerged that he hadn’t.)

Afterwards, physicists came up with alternative scheme. Imagine that you are replacing the black point in the center of the previous animation with a detector, and the rightmost red particle with a laser light source. Now you send light pulses (represented here by fast red dots) from the light source to the detector; let’s first look at this with the gravitational wave switched off:

Every time a light pulse reaches the detector, an indicator light flashes yellow. The pulses are sent out regularly, they all travel at the same speed, hence they also reach the detector in regular intervals.

If a gravitational wave passes through this system, again from the back and coming towards you, distances will change. Let us keep our camera trained on the detector, so the detector remains where it is. The changing distance to the light source, and also the changing distances between the light pulses, and some of the changes in distance between light pulses and detector or source, are due to the gravitational wave. Here is what that would look like (again, hugely exaggerated):

Keep your eye on the blinking light, and you will see that its blinking is not so regular any more. Sometimes, the light blinks faster, sometimes slower. This is an effect of the gravitational wave. An effect by which we can hope to detect the gravitational wave.

“We” in this case are the radio astronomers working on what are known as Pulsar Timing Arrays. The sender of regular pulses are pulsars, rotating neutron stars sweeping a radio beam across our antennas like a cosmic lighthouse. The detectors are radio telescopes here on Earth. Detection is anything but easy. With a single pulsar, you’d need to track pulse arrival times with an accuracy of a few billionths of a second over half a year, and make sure you are not being fooled by various other sources of timing variations. So far, no gravitational waves have been detected in this way, although the radio astronomers are keeping at it.

To see how gravitational wave detectors like LIGO work, we need to make things a little more complex.

Interferometric gravitational wave detectors: the set-up

Here is the basic set-up: Two mirrors, a receiver (or “light detector”), a light source and what is known as a beamsplitter:

Light is sent into the detector from the (laser) light source LS to the beamsplitter B which, true to its name, sends half of the light on to the mirror M1 and lets the other half through to the mirror M2. At M1 and M2, respectively, the light is reflected back to the beam splitter. There, the light arriving from M1 (or M2) is split again, with half going towards the light detector LD, the other half back in the direction of the light source LS. We will ignore the latter half and pretend, for the sake of our simplified explanation, that all the light reaching B from M1 or M2 goes on to the light detector LD.

(To avoid confusion, I will always refer to LD as the “light detector” and take the unqualified word “detector” to mean the whole setup.)

This setup, by the way, is called a Michelson Interferometer. We’ll see below why it is a good setup for gravitational wave detectors.

In what follows, we will assume that the mirrors and the beam splitter, shown as being suspended, react to the gravitational wave in the same way freely floating particles would react. The key effects are between the mirrors and the beam splitter in what are called the two arms of the detector. Arm length is huge in today’s detectors, running to a few kilometers. In comparison, light source and light detector are very close to the beamsplitter; changes of the distances between these three do not signify.

Light pulses in a gravitational wave detector

Next, let us see how light pulses run through this detector. Here is the same setup, seen from above: Light source LS, the two mirrors M1 and M2, the beamsplitter B and the light detector LD: all present and accounted for.

Next, we let the light source emit light pulses. For greater clarity, I will make two artificial and unrealistic changes. I will send red and green pulses into the detector, representing the light that goes into the horizontal and the vertical arm, respectively. In reality, there is no distinction, just light apportioned at the beamsplitter. Light running towards M1 will be offset a little to the left, light coming back from M1 to the right, for better clarity. Same goes for M2. This, too, is different in a real detector. That said, here come the light pulses: Light starts at the light source to the left. Light that has left the source together, travels together (so green and red pulses are side by side) until the beam splitter. The beam splitter then sends the green pulses on their upward journey and lets the red pulses pass on their way towards the mirror on the right. All the particles that arrive back at the beamsplitter after reflection at M1 or M2. At the beamsplitter, they are directed towards the light detector at the bottom.

In this setup, the horizontal arm is slightly longer than the vertical arm. Red particles have to cover some extra distance. That is why they arrive at the detector a bit later, and we get an alternating rhythm: green, red, green, red, with equal distances in between. This will become important later on.

Here is a diagram, a kind of registration strip, which shows the arrival times for red and green pulses at the light detector (time is measured in “animation frames”): The pattern is clear: red and green pulses arrive evenly spaced, one after the other.

Bring on the gravitational wave!

Next, let’s switch on our standard gravitational wave (exaggerated, passing through the screen towards you, and so on). Here is the result: We have trained our camera on the beamsplitter (so in our image, the beamsplitter doesn’t move). We ignore any slight changes in distance between beamsplitter and light source/light detector. Instead, we focus on the mirrors M1 and M2, which change their distance from the beamsplitter just as we would expect from the earlier animations.

Look at the way the pulses arrive at our light detector: sometimes red and green are almost evenly spaced, sometimes they close together. That is caused by the gravitational wave. Without the wave, we had strict regularity.

Here is the corresponding “registration strip” diagram. You can see that at some times, the light pulses of each color are closer together, at others, farther apart:

At the time I have marked with a hand-drawn arrow, red and green pulses arrive almost in unison!

The pattern is markedly different from the scenario without a gravitational wave. Detect this change in the pattern, and you have detected the gravitational wave.

Running interference

If you’ve wondered why detectors like LIGO are called interferometric gravitational wave detectors, we will need to think about waves a bit more. If not, let me just state that detectors like LIGO use the wave properties of light to measure the changes in pulse arrival rate you have seen in the last animation. To skip the details, feel free to jump ahead to the last section, “…and now for something a thousand times more complicated.”

Light is a wave, with crests and troughs corresponding to maxima and minima of the electric and of the magnetic field. While the animations I have shown you track the propagation of light pulses, they can also be used to understand what happens to a light wave in the interferometer. Just assume that each of the moving red and green dots in the detector marks the position of a wave crest.

Particles just add up. Take 2 particle and add 2 particles, and you will end up with 4 particles. But if you add up (combine, superimpose) waves, it depends. Sometimes, one wave plus another wave is indeed a bigger wave. Sometimes, it’s a smaller wave, or no wave at all. And sometimes it’s complicated.

When two waves are in perfect sync, the crests of the one aligning with the crests of the other, and the troughs aligning, too, you indeed get a bigger wave. The following diagram shows at which times the different parts of two light waves arrive at the light detector, and how they add up. (I’ve placed a dot on top of each crest; that is what the dots where meant to signify, after all.) On top, the green wave, perfectly aligned with the red wave (which, for clarity, is shown directly below the green wave). Add the two waves up, and you will get the (markedly stronger) blue wave in the bottom panel.

Not so if the two waves are maximally misaligned, the crests of each aligned with the troughs of the other. A crest and a trough cancel each other out. The sum of a wave and a maximally misaligned wave of equal strength is: no wave at all. Here is the corresponding diagram: Recall that this was exactly the setup for our gravitational wave detector in the absence of gravitational waves: Red and green pulses with equal spacing; troughs of the one wave perfectly aligned with the crests of the other. The result: No light at the light detector. (For realistic gravitational wave detectors, that is almost true.)

When a gravitational wave passes through the detector, the situation changes. Here is the corresponding pattern of pulse/wave crest arrival times for the animation above: The blue pattern, which is the sum of the red and the green, is complex. But it is not a flat line. There is light at the light detector where there was no light before, and the cause of the change is the gravitational wave passing through.

All in all, this makes a (highly simplified) version of how gravitational wave detectors such as LIGO work. Whatever the scientists will report this Thursday, it is based on light signals at the exit of such an interferometric detector.

And now for something a thousand times more complicated

Real gravitational wave detectors are, of course, much more complicated than that. I haven’t even started talking about the many disturbances scientists need to take into account – and to suppress as far as possible. How do you suspend the mirrors so that (at least for certain gravitational waves) they will indeed be influenced as if they were freely floating particles? How do you prevent seismic noise, cars or trains in the wider neighborhood and so on from moving your mirrors a tiny little bit (either by vibrations or by their own gravity)? What about fluctuations of the laser light?

Gravitational wave hunting is largely a hunt for noise, and for ways of suppressing that noise. The LIGO gravitational wave detectors and their kin are highly complex machines, with hundreds of control circuits, highly elaborate mirror suspensions, the most stable lasers known to physics (and some of the most high-powered). The technology has been contributed by numerous group from all over the world.

But all this is taking us too far, and I refer you to the pages of the detectors and collaborations for additional information:

LIGO pages at Caltech

Pages of the LIGO Scientific Collaboration

GEO 600 pages

VIRGO / EGO pages

You can find some further information about gravitational waves on the Einstein Online website:

Einstein Online: Spotlights on gravitational waves

Update: Gravitational Waves Discovered

February 8, 2016February 11, 2016 by Markus Pössel

Gravitational Waves and How They Distort Space

Gravitational waves distort space in a rhythmic fashion. These simple animations show how. — That's not a space worm. It's what a gravitational wave does to space according to Einstein's theory of general relativity.

It’s official: on February 11, 10:30 EST, there will be a big press conference about gravitational waves by the people running the gravitational wave detector LIGO. It’s a fair bet that they will announce the first direct detection of gravitational waves, predicted by Albert Einstein 100 years ago. If all goes as the scientists hope, this will be the kick-off for an era of gravitational wave astronomy: for learning about some of the most extreme and violent events in the cosmos by measuring the tiny ripples of space distortions that emanate from them.

Time to brush up on your gravitational wave knowledge, if you haven’t already done so! Here’s a visualization to help you – and we’ll go step by step to see what it means:

Einstein’s distorted spacetime

In the words of the eminent relativist John Wheeler, Einstein’s theory of general relativity can be summarized in two statements: Matter tells space and time how to curve. And (curved) space and time tell matter how to move. (Here is a slightly longer version on Einstein Online.)

Einstein published the final form of his theory in November 1915. By spring 1916, he had realized another consequence of distorting space and time: general relativity allows for gravitational waves, rhythmic distortions which propagate through space at the speed of light.

For quite some time, physicists weren’t sure whether these gravitational waves were real or a mathematical artifact within Einstein’s theory. (For more about this controversy, see Daniel Kennefick’s book “Traveling at the Speed of Thought and this article.) But since the 1980s, there has been indirect evidence for these waves (which earned its discoverers a Nobel prize, no less, in 1993).

Gravitational waves are emitted by orbiting bodies and certain other accelerated masses. Right now, major international efforts are underway to detect gravitational waves directly. Once detection is possible, the scientists hope to use gravitational waves to “listen” to some of the most violent processes in the universe: merging black holes and/or neutron stars, or the core region of supernova explosions.

Just as regular astronomy uses light and other forms of electromagnetic radiation to learn about distant objects, gravitational wave astronomy will decipher the information contained within gravitational waves. And if you go by recent rumors, gravitational wave astronomy might already have kicked off in mid-September 2015.

What do gravitational waves do?

But what do gravitational waves do? For that, let us look at a simplified, entirely hypothetical situation. (The following are variations on images and animations originally published here on Einstein Online.) Consider particles drifting in space, far from any sources of gravity. Imagine that the particles (red) are arranged in a circle around a center (marked in black):

If a simple gravitational wave were to pass through this image, coming directly at the reader, distances between these particles would change rhythmically as follows:

Note the distinctive pattern: When the circle is stretched in the vertical direction, it is compressed in the horizontal direction, and vice versa. That’s typical for gravitational waves (“quadrupole distortion”).

It’s important to keep in mind that this animation, and the ones that will follow, exaggerate the gravitational wave’s effect quite considerably. The gravitational waves detectors such as aLIGO hope to measure are much, much weaker. If our hypothetical circle of particles were as large as the Earth’s orbit around the Sun, a realistic gravitational wave would distort it by less than the diameter of a hydrogen atom.

Gravitational waves moving through space

The animation above shows what could be called a “gravitational oscillation.” To see the whole wave, we need to consider the third dimension.

We talk about a wave when oscillations propagate through space. Consider a water wave: At each point of the surface, we have an oscillation, with the surface rising and falling rhythmically. But it’s only the fact that this oscillation propagates, and that we can see a crest moving over the surface, that makes this into a wave.

It’s the same with gravitational waves. To see that, we will look not at a single circle of freely floating particles, but at many such circles, stacked one behind the other, forming the surface of a cylinder:

In this image, it’s hard to see which points are in front and which in the back. Let us join each particle to its nearest neighbors with a blue line, and let us also fill out the area between those lines. That way, the geometry is much more obvious:

Just remember that neither the lines nor the whitish surface is physical. On the contrary, if we want the particles to be maximally susceptible to the effect of the gravitational wave, we should make sure they are truly floating freely, and certainly they shouldn’t be linked in any way!

Now, let us see what the same gravitational wave we saw before does to this assembly of particles. From this perspective, the wave is passing from the right-hand side in the back towards the left-hand side on the front: As you can see, the wave is propagating through space. For instance, the point where the vertical distances within the circle of particles is maximal is moving towards the observer. The wave nature can be seen even more clearly if we look at this cylinder directly from the side:

What the animations show is just one kind of simple gravitational wave (“linearly polarized”). Here is another kind (“circularly polarized”):

This, then, is what the gravitational wave hunters are looking for. Except that they do not have particles floating in free space. Instead, their detectors contain test masses (notably large mirrors) elaborately suspended here on Earth, with laser light to detect the minute distance changes caused by gravitational waves.

More realistic gravitational wave signals, which contain information about merging black holes or the bulk motion of matter inside a supernova explosion, are more complicated still. They combine many simple waves of different frequencies, and the strength of such waves (their amplitude) will change over time in a characteristic fashion.

In these animations, gravitational waves look a bit like wriggling space worms. But these space worms could become the astronomers’ best friends, carrying information about the cosmos that is hard or even impossible to obtain in any other way.

[Don’t miss the sequel: Gravitational wave detectors: how they work]

Update: Gravitational Waves Detected

February 1, 2016February 23, 2017 by Fraser Cain

What is the Higgs Boson?

What is this thing we keep hearing about – the Higgs Boson, and why is it important?

Continue reading “What is the Higgs Boson?”

January 13, 2016January 13, 2016 by Matt Williams

What Are The Uses Of Electromagnets?

The Large Hadron Collider at CERN. Credit: CERN/LHC

Electromagnetism is one of the fundamental forces of the universe, responsible for everything from electric and magnetic fields to light. Originally, scientists believed that magnetism and electricity were separate forces. But by the late 19th century, this view changed, as research demonstrated conclusively that positive and negative electrical charges were governed by one force (i.e. magnetism).

Since that time, scientists have sought to test and measure electromagnetic fields, and to recreate them. Towards this end, they created electromagnets, a device that uses electrical current to induce a magnetic field. And since their initial invention as a scientific instrument, electromagnets have gone on to become a regular feature of electronic devices and industrial processes.

Continue reading “What Are The Uses Of Electromagnets?”

December 15, 2015April 7, 2016 by Matt Williams

What Are The Parts Of An Atom?

A depiction of the atomic structure of the helium atom. Credit: Creative Commons

Since the beginning of time, human beings have sought to understand what the universe and everything within it is made up of. And while ancient magi and philosophers conceived of a world composed of four or five elements – earth, air, water, fire (and metal, or consciousness) – by classical antiquity, philosophers began to theorize that all matter was actually made up of tiny, invisible, and indivisible atoms.

Since that time, scientists have engaged in a process of ongoing discovery with the atom, hoping to discover its true nature and makeup. By the 20th century, our understanding became refined to the point that we were able to construct an accurate model of it. And within the past decade, our understanding has advanced even further, to the point that we have come to confirm the existence of almost all of its theorized parts.

Continue reading “What Are The Parts Of An Atom?”

November 16, 2015December 23, 2015 by Vanessa Janek

Cosmologist Thinks a Strange Signal May Be Evidence of a Parallel Universe

A simulation of galaxies during the era of deionization in the early Universe. Credit: M. Alvarez, R. Kaehler, and T. AbelCredit: M. Alvarez, R. Kaehler, and T. Abel

In the beginning, there was chaos.

Hot, dense, and packed with energetic particles, the early Universe was a turbulent, bustling place. It wasn’t until about 300,000 years after the Big Bang that the nascent cosmic soup had cooled enough for atoms to form and light to travel freely. This landmark event, known as recombination, gave rise to the famous cosmic microwave background (CMB), a signature glow that pervades the entire sky.

Now, a new analysis of this glow suggests the presence of a pronounced bruise in the background — evidence that, sometime around recombination, a parallel universe may have bumped into our own.

Although they are often the stuff of science fiction, parallel universes play a large part in our understanding of the cosmos. According to the theory of eternal inflation, bubble universes apart from our own are theorized to be constantly forming, driven by the energy inherent to space itself.

Like soap bubbles, bubble universes that grow too close to one another can and do stick together, if only for a moment. Such temporary mergers could make it possible for one universe to deposit some of its material into the other, leaving a kind of fingerprint at the point of collision.

Ranga-Ram Chary, a cosmologist at the California Institute of Technology, believes that the CMB is the perfect place to look for such a fingerprint.

This image, the best map ever of the Universe, shows the oldest light in the universe. This glow, left over from the beginning of the cosmos called the cosmic microwave background, shows tiny changes in temperature represented by color. Credit: ESA and the Planck Collaboration. — The cosmic microwave background (CMB), a pervasive glow made of light from the Universe’s infancy, as seen by the Planck satellite in 2013. Tiny deviations in average temperature are represented by color. Credit: ESA and the Planck Collaboration.

After careful analysis of the spectrum of the CMB, Chary found a signal that was about 4500x brighter than it should have been, based on the number of protons and electrons scientists believe existed in the very early Universe. Indeed, this particular signal — an emission line that arose from the formation of atoms during the era of recombination — is more consistent with a Universe whose ratio of matter particles to photons is about 65x greater than our own.

There is a 30% chance that this mysterious signal is just noise, and not really a signal at all; however, it is also possible that it is real, and exists because a parallel universe dumped some of its matter particles into our own Universe.

After all, if additional protons and electrons had been added to our Universe during recombination, more atoms would have formed. More photons would have been emitted during their formation. And the signature line that arose from all of these emissions would be greatly enhanced.

Chary himself is wisely skeptical.

“Unusual claims like evidence for alternate Universes require a very high burden of proof,” he writes.

Indeed, the signature that Chary has isolated may instead be a consequence of incoming light from distant galaxies, or even from clouds of dust surrounding our own galaxy.

SO is this just another case of BICEP2? Only time and further analysis will tell.

Chary has submitted his paper to the Astrophysical Journal. A preprint of the work is available here.

October 13, 2015December 23, 2015 by Vanessa Janek

Shape-shifting neutrinos earn physicists the 2015 Nobel

Super-Kamiokande, a neutrino detector in Japan, holds 50,000 tons of ultrapure water surrounded by light tubes. Credit: Super-Kamiokande Observatory

What do Albert Einstein, Neils Bohr, Paul Dirac, and Marie Curie have in common? They each won the Nobel prize in physics. And today, Takaaki Kajita and Arthur McDonald have joined their ranks, thanks to a pioneering turn-of-the-century discovery: in defiance of long-held predictions, neutrinos shape-shift between multiple identities, and therefore must have mass.

The neutrino, a slight whiff of a particle that is cast off in certain types of radioactive decay, nuclear reactions, and high-energy cosmic events, could be called… shy. Electrically neutral but enormously abundant, half the time a neutrino could pass through a lightyear of lead without interacting with a single other particle. According to the Standard Model of particle physics, it has a whopping mass of zero.

As you can imagine, neutrinos are notoriously difficult to detect.

But in 1956, scientists did exactly that. And just a few years later, a trio of physicists determined that neutrinos came in not just one, not two, but three different types, or flavors: the electron neutrino, the muon neutrino, and the tau neutrino.

The first annotated neutrino event. Image credit: — The neutrino was first detected in 1956 by Clyde Cowan and Frederick Reines. In 1970, scientists captured the first image of a neutrino track in a hydrogen bubble chamber. *Image: Argonne National Laboratory*

But there was a problem. Sure, scientists had figured out how to detect neutrinos—but they weren’t detecting enough of them. In fact, the number of electron neutrinos arriving on Earth due to nuclear reactions in the Sun’s core was only one-third to one-half the number their calculations had predicted. What, scientists wondered, was happening to the rest?

Kajita, working at the Super-Kamiokande detector in Japan in 1998, and McDonald, working at the Sudbury Neutrino Observatory in Canada in 1999, determined that the electron neutrinos were not disappearing at all; rather, these particles were changing identity, spontaneously oscillating between the three flavor-types as they traveled through space.

Moreover, the researchers proclaimed, in order for neutrinos to make such transformations, they must have mass.

This is due to some quantum funny business having to do with the oscillations themselves. Grossly simplified, a massless particle, which always travels at the speed of light, does not experience time—Einstein’s theory of special relativity says so. But change takes time. Any particle that oscillates between identities needs to experience time in order for its state to evolve from one flavor to the the next.

The interior structure of the Sun. Credit: Wikipedia Commons/kelvinsong — Neutrinos are produced in abundance during fusion reactions at the center of our Sun, and oscillate between three different types, or *flavors*, on their way to Earth. *Image: Wikipedia Commons/kelvinsong*

Kajita and McDonald’s work showed that neutrinos must have a mass, albeit a very small one. But neutrinos are abundant in the Universe, and even a small mass has a large effect on all sorts of cosmic phenomena, from solar nuclear physics, where neutrinos are produced en masse, to the large-scale evolution of the cosmos, where neutrinos are ubiquitous.

The neutrino, no longer massless, is now considered to play a much larger role in these processes than scientists had originally believed.

What is more, the very existence of a massive neutrino undermines the theoretical basis of the Standard Model. In fact, Kajita’s and McDonald’s discovery provided some of the first evidence that the Standard Model might not be as airtight as had been previously believed, nudging scientists ever more in the direction of so-called “new physics.”

This is not the first time physicists have been awarded a Nobel prize for research into the nature of neutrinos. In 1988, Leon Lederman, Melvin Schwartz, and Jack Steinberger were awarded the prize for their discovery that neutrinos come in three flavors; in 1995, Frederick Reines won a Nobel for his detection of the neutrino along with Clyde Cowan; and in 2002, a Nobel was awarded to Raymond David Jr., the oldest person ever to receive a the prize in physics, and Masatoshi Koshiba for their detection of cosmic neutrinos.

Kajita, of the University of Tokyo, and McDonald, of Queen’s University in Canada, were awarded the prestigious prize this morning at a news conference in Stockholm.