Catching Waves

I’m afraid this post isn’t about the best surf spots out there but a different type of waves, gravitational waves – big news for physicists in the last year. In 1915 they were predicted by Einstein as a product of his theory of general relativity and in 2015, on the theory’s 100th anniversary, their existence was verified – but what is all the fuss about and how did the long awaited detection come about? Let’s recap.

Now if you’ve read some of my previous posts you’ll be familiar with the term ‘spacetime’ the continuum (or manifold to speak mathematically) of the four dimensions – three of space and one of time. As we know, masses create distortion or ‘bending’ of their surrounding spacetime – just like a bowling ball creates a dip if placed on a trampoline. If masses then accelerate the continual changing in the distortion of their surrounding spacetime will cause ripples to occur – just like the ripples produced on the surface of a pond when a pebble is dropped in it or a duck accelerates through the water. These outward ripples act like waves and transporting energy in the form of gravitational radiation. These waves are very similar to electromagnetic waves, which transport a form of radiant energy, for example visible light. These electromagnetic waves travel at a speed of c, colloquially ‘the speed of light’ and hey presto so do gravitational waves. In a nutshell gravitational waves can be thought of as ripples in the curvature of spacetime due to the acceleration of masses.

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Now what is the effect of these gravitational waves? Well the ripples in the fabric of spacetime signify the changing of the amount of space between objects. Because it is spacetime itself that is rippling it is spacetime itself that is being distorted by the acceleration of the masses. If two objects A and B had a certain amount of space between them, a gravitational wave could cause this space to expand or contract. But there is a catch. How do we measure such shifting of space? A conventional ruler wouldn’t work! Think about it, if we put a marker on the floor by A and a marker on the floor by B the gravitational wave will cause the space between the markers on the floor to also expand or contract relative to each other and hence we would notice no difference! We need a special ruler and for this we use the speed of light. If the space between two objects expands light will take longer to travel from one object to the other and it is through measurements like these we can detect the waves. Cue the LIGO experiment – Laser Interferometer Gravitational-Wave Observatory.

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The LIGO experiment has 4 kilometre long tunnels and uses lasers to measure the changes in the distance between the ends of the tunnels. The tunnels are set up perpendicular to each other so that when a gravitational waves passes through one of the tunnels is contracted and the other is expanded. Now the source masses and precision involved in order to produce a valid detection are very high .Gravitational waves are produced whenever any masses accelerate – for example if two sharks whirl around a circle, gravitational waves will occur (as well as water waves of course!). However the gravitational force is the weakest of all the fundamental forces and seeing as the mass of the sharks is very small on the astronomical scale of things the magnitude of these gravitational waves will be pretty much negligible. We need big masses in order to produce detectable waves, i’m talking black hole heavy.

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The waves given off by the cataclysmic final merger of two distant black holes (GW150914), reached Earth after travelling over a billion lightyears, as a ripple in spacetime that changed the length of a 4km LIGO arm by a ten thousandth of the width of a proton – this is a noticying the difference of a few parts in 10^-23 meters! If you can’t visualise the sheer infinitesimal scale of these numbers try this – it is proportionally equivalent to changing the distance from us to the nearest star outside the Solar System (Alpha Centauri) by one hair’s width and being able to measure this!  My mind is blown, if yours isn’t you must have inhumanly fat hairs on your head. And on top of all this you need an amazing data analysis capabilities to cancel out all the random noise that could interfere with the signal -like identifying a whisper in a noisy room. All these factors make even the most extreme gravitational waves uncatchable on Earth by any means other than the most sophisticated detectors, like LIGO, who confirmed their findings last year.

Now that we know with certainty that gravitational waves are out there, more advanced versions of LIGO are to be created such as LISA – a space-based gravitational wave detector operating on much larger scales than LIGO which, being in space, won’t have to worry about things such as seismic effects messing up the readings. Our ability to scour the skies for gravitational waves opens up a completely new way to study the universe, almost like discovering a new sense with which to investigate our surroundings. The waves will reveal the cataclysmic explosions and collisions occurring throughout the far reaches of the universe. A plethora of events such as spinning neutrons stars, supernova, black holes emit gravitational waves and now that our ears are opened we can finally tune into the sound of orchestral universe.

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15 responses to “Catching Waves

  1. I had heard the flexible membrane metaphor previously but your mention set me thinking and since a flexible membrane, like a pendulum, set me wondering about the concept. The gravity wave experiment depended upon a massive time-space distortion when two black holes collided but there seems to be an assumption that there is a neutral point in time-space which we identify with what we call present time (which is assumed to be an illusion in a static space time volume). A couple of thoughts occurred to me. These waves in space-time are obviously no illusion ut a real bounce of whatever the hell is out there and if the bounce is real, is it possible to bounce that heavy mass at the bottom of a black hole out again into standard space….and what direction would it bounce towards? The gravity wave indicates some vague possibility there but the force strong enough to bounce a black hole seems it would be forever beyond the human efforts to accomplish but lots of other impossibilities have been accomplished like the election of Trump. Bouncing a black hole might be a slam-dunk in comparison.

    On Thu, Feb 23, 2017 at 1:16 PM, Rationalising The Universe wrote:

    > Mekhi posted: “I’m afraid this post isn’t about the best surf spots out > there but a different type of waves, gravitational waves – big news for > physicists in the last year. In 1915 they were predicted by Einstein as a > product of his theory of general relativity and in 2” >

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    • Hi Jiisand, so to address your first point about time – I don’t myself see it as a neutral point in space time which is the present, instead because we humans all co-exist in an environment which resides in the same gravitational potential we all agree on how we measure the passing of time. So for us we can all agree on what is happening in the present moment. It’s not that our spot in the universe is the neutral point but that we all experience the same passing of time, hence from our perspective we can define what we all mutually agree on as happening now as the present in the universe. Secondly, yes the gravitational waves are indeed real distortions of space-time. However all the waves do is stretch and compress the space between objects so I do not believe they could be used as a means of permanently displacing an object away from an other, or ‘bouncing the heavy mass out of the black hole’ as you say. Obviously if we have a very large mass we can exert a gravitational force to attract the object towards us but when faced against a black hole as our adversary we have no chance in winning! I hope this makes pseudo-sense!

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  2. Precision beyond my wildest dreams ; detecting the undetectable. One question ; a large rock will make bigger ripples than a pebble but if the pebble is a lot nearer it will out ripple the rock. So why not go for smaller nearer disturbances? In fact aren’t disturbances everywhere so how do we know we have distinguished them?

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  3. To me, gravity seems to be an example of “spooky action at a distance”, two masses, physically unconnected, yet drawing each other closer.

    The wave would seem to me to be a kind of vibration, as each of the two black holes came closer and then farther from the Earth, as the black holes whirled around each other.

    Propagation. Does propagation follow the same speed changes as a bowling ball dropped from the leaning tower of Pisa? I mean, the speed of falling increases by some formula, does that same formula apply to the disturbance in the Earth’s position caused by the two black holes?

    And the Earth would be affected to a lesser or greater degree by the movement of all cosmological objects, according to their mass and distance?

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