Beyond Spacetime: Gravitational Waves Might Reveal Extra-Dimensions

gw-ripples
NASA (edit by Ian O’Neill)

We are well and truly on our way to a new kind of astronomy that will use gravitational waves — and not electromagnetic waves (i.e. light) — to “see” a side of the universe that would otherwise be invisible.

From crashing black holes to wobbling neutron stars, these cosmic phenomena generate ripples in spacetime and not necessarily emissions in the electromagnetic spectrum. So when the Laser Interferometer Gravitational-wave Observatory (LIGO) made its first gravitational wave detection in September 2015, the science world became very excited about the reality of “gravitational wave astronomy” and the prospect of detecting some of the most massive collisions that happen in the dark, billions of light-years away.

Like waves rippling over the surface of the ocean, gravitational waves travel through spacetime, a prediction that was made by Albert Einstein over a century ago. And like those ocean waves, gravitational waves might reveal something about the nature of spacetime.

We’re talking extra-dimensions and a new study suggests that gravitational waves may carry an awful lot more information with them beyond the characteristics of what generated them in the first place.

Our 4-D Playing Field

First things first, remember that we interact only with four-dimensional spacetime: three dimensions of space and one dimension of time. This is our playing field; we couldn’t care less whether there are more dimensions out there.

Unless you’re a physicist, that is.

And physicists are having a hard job describing gravity, to put it mildly. This might seem weird considering how essential gravity is for, well, everything. Without gravity, no stars would form, planets wouldn’t coalesce and the cosmos would be an exceedingly boring place. But gravity doesn’t seem to “fit” with the Standard Model of physics. The “recipe” for the universe is perfect, except it’s missing one vital ingredient: Gravity. (It’s as if a perfect cake recipe is missing one crucial ingredient, like flour.)

There’s another weird thing about gravity: Although it’s very important in our universe (yes, there might be more than one universe, but I’ll get to that later), it is actually the weakest of all forces.

But why so weak? This is where string theory comes in.

String theory (and, by extension, superstring theory) predicts that the universe is composed of strings that vibrate at different frequencies. These strings form something like a vast, superfine noodle soup and these strings thread through many dimensions (many more than our four-dimensions) creating all the particles and forces that we know and love.

Now, the possible reason why gravity is so weak when compared with the other fundamental forces could be that gravity is interacting with many more dimensions that are invisible to us 4-D beings. Although string theory is a wonderful mathematical tool to describe this possibility, there is little physical evidence to back up this superfine noodly mess, however.

But as already mentioned, if string theory holds true, it would mean that our universe contains many more dimensions than we regularly experience. (The unifying superstring theory, called “M-theory”, predicts a total of 11 dimensions and may provide the framework that unifies the fundamental forces and could be the diving board that launches us into the vast ocean that is the multiversebut I’ll stop there, I’ve said too much.)

Groovy. But what the heck has this got to do with gravitational waves? As gravitational waves travel through spacetime, they might be imprinted with information about these extra dimensions. Like our wave analogy, as the sea washes over a beach, the frequency of the waves increase as the water becomes shallower — the ocean waves are imprinted with information about how deep the water is. Could gravitational waves washing over (or, more accurately, through) spacetime also create some kind of signature that would reveal the presence of very, very tiny extra-dimensions as predicted by superstring theory?

Possibly, say researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam, Germany.

“Physicists have been looking for extra dimensions at the Large Hadron Collider at CERN but up to now this search has yielded no results,” says Gustavo Lucena Gómez, second author of a new study published in the Journal of Cosmology and Astroparticle Physics. “But gravitational wave detectors might be able to provide experimental evidence.”

Beyond Spacetime?

The researchers suggest that these extra-dimensions might modify the signal of gravitational waves received by detectors like LIGO and leave a very high-frequency “fingerprint.” But as this frequency would be exceedingly high — of the order of 1000 Hz — it’s not conceivable that the current (and near-future) ground-based gravitational wave detectors will be sensitive enough to even hope to detect these frequencies.

However, extra-dimensions might modify the gravitational waves in a different way. As gravitational waves propagate, they stretch and shrink the spacetime they travel through, like this:

gw-waves-wave

The amount of spacetime warping might therefore be detected as more gravitational wave detectors are added to the global network. Currently, LIGO has two operating observing stations (one in Washington and one in Louisiana) and next year, the European Virgo detector will start taking data.

More detectors are planned elsewhere, so it’s possible that we may, one day, use gravitational waves to not only “see” black holes go bump in the night, we might also “see” the extra-dimensions that form the minuscule tapestry of the fabric beyond spacetime. And if we can do this, perhaps we’ll finally understand why gravity is so weak and how it really fits in with the Standard Model of physics.

Want to know more about gravitational waves? Well, here’s an Astroengine YouTube video on the topic:

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When Black Holes Collide… Astroengine Is Now On YouTube!

So… it begins!

Astroengine has finally been launched on YouTube, kicking off with a summary of the recent gravitational wave discovery by LIGO. I’m aiming to produce at least one video a week and I’d really like to make it as viewer-driven as possible. So if you have any burning space science questions or any critique about the videos I’m posting, please reach out!

But for now, you know what to do: like, subscribe and enjoy!

Holographic Universe: Fermilab to Probe Smallest Space-Time Scales

Conceptual design of the Fermilab holometer (Fermilab)
Conceptual design of the Fermilab holometer (Fermilab)

During the hunt for the predicted ripples in space-time — known as gravitational waves — physicists stumbled across a rather puzzling phenomenon. Last year, I reported about the findings of scientists using the GEO600 experiment in Germany. Although the hi-tech piece of kit hadn’t turned up evidence for the gravitational waves it was seeking, it did turn up a lot of noise.

Before we can understand what this “noise” is, we need to understand how equipment designed to look for the space-time ripples caused by collisions between black holes and supernova explosions.

Gravitational wave detectors are incredibly sensitive to the tiniest change in distance. For example, the GEO600 experiment can detect a fluctuation of an atomic radius over a distance from the Earth to the Sun. This is achieved by firing a laser down a 600 meter long tube where it is split, reflected and directed into an interferometer. The interferometer can detect the tiny phase shifts in the two beams of light predicted to occur should a gravitational wave pass through our local volume of space. This wave is theorized to slightly change the distance between physical objects. Should GEO600 detect a phase change, it could be indicative of a slight change in distance, thus the passage of a gravitational wave.

While looking out for a gravitational wave signal, scientists at GEO600 noticed something bizarre. There was inexplicable static in the results they were gathering. After canceling out all artificial sources of the noise, they called in the help of Fermilab’s Craig Hogan to see if his expertise of the quantum world help shed light on this anomalous noise. His response was as baffling as it was mind-blowing. “It looks like GEO600 is being buffeted by the microscopic quantum convulsions of space-time,” Hogan said.

Come again?

The signal being detected by GEO600 isn’t a noise source that’s been overlooked, Hogan believes GEO600 is seeing quantum fluctuations in the fabric of space-time itself. This is where things start to get a little freaky.

According to Einstein’s view on the universe, space-time should be smooth and continuous. However, this view may need to be modified as space-time may be composed of quantum “points” if Hogan’s theory is correct. At its finest scale, we should be able to probe down the “Planck length” which measures 10-35 meters. But the GEO600 experiment detected noise at scales of less than 10-15 meters.

As it turns out, Hogan thinks that noise at these scales are caused by a holographic projection from the horizon of our universe. A good analogy is to think about how an image becomes more and more blurry or pixelated the more you zoom in on it. The projection starts off at Planck scale lengths at the Universe’s event horizon, but its projection becomes blurry in our local space-time. This hypothesis comes out of black hole research where the information that falls into a black hole is “encoded” in the black hole’s event horizon. For the holographic universe to hold true, information must be encoded in the outermost reaches of the Universe and it is projected into our 3 dimensional world.

But how can this hypothesis be tested? We need to boost the resolution of a gravitational wave detector-type of kit. Enter the “Holometer.”

Currently under construction in Fermilab, the Holometer (meaning holographic interferometer) will delve deep into this quantum realm at smaller scales than the GEO600 experiment. If Hogan’s idea is correct, the Holometer should detect this quantum noise in the fabric of space-time, throwing our whole perception of the Universe into a spin.

For more on this intriguing experiment, read the Symmety Magazine article “Hogan’s holometer: Testing the hypothesis of a holographic universe.”

Detecting Gravitational Waves on the Cheap

Forget building gravitational wave detectors costing hundreds of millions of dollars (I’m looking at you, LIGO), make use of the most accurate cosmic timekeepers instead and save a bundle.

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) is a proposal that involves closely monitoring the regular flashes of spinning neutron stars (or pulsars) to detect very slight “shimmers” in their signal. Although the physics is crazy-complex, by tracking these shimmers over a suitably distributed number of pulsars could reveal the passage of gravitational waves.

However, there’s a problem with this plan; pulsars are notoriously tricky stellar objects, as my colleague Jennifer Ouellette points out:

The problem is that you need to closely monitor rapidly-spinning millisecond pulsars, which are (a) tough to find (only 150 have been found over nearly three decades since pulsars were first discovered), and (b) not very plentiful in the part of the night sky of interest to scientists (northern hemisphere). They tend to clump together in globular star clusters, which makes them useless for detecting gravitational waves.

However, according to results announced by the National Radio Astronomy Observatory (NRAO) at this week’s American Astronomical Society (AAS) meeting in Washington D.C., they’ve discovered 17 new pulsars with the help of NASA’s Fermi Gamma-Ray Space Telescope.

In addition to recent Fermi telescope pulsar discoveries, it would appear that the number of potential targets for NANOGrav are increasing, making a stronger case for the 10 year, $65 million project…

You have to wonder whether building the Laser Interferometer Gravitational-Wave Observatory (LIGO) was worth it (but you can’t be too careful, some terrorist organizations might want to use gravitational waves for evil, so it would be good if we detected them first).

Source: Discovery News

Did Gravitational Waves Ring a Bell in 1987?

Gravitational waves generated by a binary system (MIT)
Gravitational waves generated by a binary system (MIT)

The hunt for gravitational waves continue, but unfortunately all gravitational wave hunters around the world are churning up nothing. Just noise. Could it be that this consequence of Einstein’s theory of General Relativity is horribly flawed? Probably not. Still, the search for these elusive waves has foxed physicists for many years. It has even come to the point that the laser interferometers used in an attempt to detect the tiny (and I mean TINY) changes in distances (as when the gravitational wave passes through us, space-time experiences a minuscule compression or expansion) have become so precise, the director of Fermilab thinks a German-UK gravitational wave detector is starting to detect the quanta of space-time itself.

However, do you ever get the feeling that we might be trying too hard? What if gravitational waves have already been detected? Say if these notoriously difficult ripples in space-time were detected over 20 years ago without using a laser interferometer? It turns out that an overlooked scientist may have found the answer to the gravitational wave problem by using nothing more than some aluminium bars and a well-timed supernova…
Continue reading “Did Gravitational Waves Ring a Bell in 1987?”

Is the Universe a Holographic Projection?

Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)
Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)

Could our cosmos be a projection from the edge of the observable Universe?

Sounds like a silly question, but scientists are seriously taking on this idea. As it happens, a gravitational wave detector in Germany is turning up null results on the gravitational wave detection front (no surprises there), but it may have discovered something even more fundamental than a ripple in space-time. The spurious noise being detected at the GEO600 experiment has foxed physicists for some time. However, a particle physicist from the accelerator facility Fermilab has stepped in with his suspicion that the GEO600 “noise” may not be just annoying static, it might be the quantum structure of space-time itself
Continue reading “Is the Universe a Holographic Projection?”

Can Gravitational Waves be Used for Evil?

Theoretical gravitational waves generated after a black hole collision. Can we surf them?
Theoretical gravitational waves generated after a black hole collision. Can we surf them?

Gravitational waves are a theoretical consequence of a propagating energy disturbance through space-time. They are predicted by Einstein’s general relativity equations, and astrophysicists are going to great pains to try to detect the faint signature from the passage of these waves through local space. Unfortunately, even though millions of dollars have been spent on international experiments, the gravitational wave remains in equation form; there is little (direct) evidence to support their existence.

However, this doesn’t stop the US military from worrying about them and commissioned a 40-page report into whether high frequency gravitational waves could be used by an enemy. Excuse me? Gravitational waves… as a weapon?
Continue reading “Can Gravitational Waves be Used for Evil?”