Gravitational waves are disturbances in space-time, the very fabric of the universe, that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction. The simplest example is a binary system, where a pair of stars or compact objects (like black holes) orbit their common center of mass.
We can think of gravitational effects as curvatures in space-time. Earth’s gravity is constant and produces a static curve in space-time. A gravitational wave is a curvature that moves through space-time much like a water wave moves across the surface of a lake. It is generated only when masses are speeding up, slowing down or changing direction.
Did you know Earth also gives off gravitational waves? Earth orbits the sun, which means its direction is always changing, so it does generate gravitational waves, although extremely weak and faint.
What do we learn from these waves?
Observing gravitational waves would be a huge step forward in our understanding of the evolution of the universe, and how large-scale structures, like galaxies and galaxy clusters, are formed.
Gravitational waves can travel across the universe without being impeded by intervening dust and gas. These waves could also provide information about massive objects, such as black holes, that do not themselves emit light and would be undetectable with traditional telescopes.
Just as we need both ground-based and space-based optical telescopes, we need both kinds of gravitational wave observatories to study different wavelengths. Each type compliments the other.
Ground-based: For optical telescopes, Earth’s atmosphere prevents some wavelengths from reaching the ground and distorts the light that does.
Space-based: Telescopes in space have a clear, steady view. That said, telescopes on the ground can be much larger than anything ever launched into space, so they can capture more light from faint objects.
How does this relate to Einstein’s theory of relativity?
The direct detection of gravitational waves is the last major prediction of Einstein’s theory to be proven. Direct detection of these waves will allow scientists to test specific predictions of the theory under conditions that have not been observed to date, such as in very strong gravitational fields.
In everyday language, “theory” means something different than it does to scientists. For scientists, the word refers to a system of ideas that explains observations and experimental results through independent general principles. Isaac Newton’s theory of gravity has limitations we can measure by, say, long-term observations of the motion of the planet Mercury. Einstein’s relativity theory explains these and other measurements. We recognize that Newton’s theory is incomplete when we make sufficiently sensitive measurements. This is likely also true for relativity, and gravitational waves may help us understand where it becomes incomplete.
A century after being proposed by physicist Albert Einstein, scientists have made the first detection of gravitational waves – massive celestial objects on the move causing spacetime itself to ripple – a historic discovery that opens up an entirely new way of studying the cosmos.
The detection was made by the twin LIGO interferometers on Sept. 14, 2015, located in Livingston, La., and Hanford, Wash., just two days after the system was significantly upgraded to boost its sensitivity.
Gravitational radiation has been directly detected. The first-ever detection was made by both facilities of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Washington and Louisiana simultaneously last September. After numerous consistency checks, the resulting 5-sigma discovery was published today. The measured gravitational waves match those expected from two large black holes merging after a death spiral in a distant galaxy, with the resulting new black hole momentarily vibrating in a rapid ringdown.
A phenomenon predicted by Einstein, the historic discovery confirms a cornerstone of humanity’s understanding of gravity and basic physics. It is also the most direct detection of black holes ever. The featured illustration depicts the two merging black holes with the signal strength of the two detectors over 0.3 seconds superimposed across the bottom. Expected future detections by Advanced LIGO and other gravitational wave detectors may not only confirm the spectacular nature of this measurement but hold tremendous promise of giving humanity a new way to see and explore our universe.
Somewhere very far away, a long time ago, two black holes smashed into each other.
One was around 36 times more massive than the Sun, and the other 29 times more massive.
So devastatingly powerful was this event that it did something that might not even be obvious to most of us: it sent a sort of ‘quake’ through the fabric of spacetime.
The power radiated by the combining of the black holes is estimated to be more than the combined light power of all the stars and galaxies in the observable universe.
This ripple event is something known as a ‘gravitational wave’ and we’ve known about them for a very long time ~ sort of.
Einstein predicted their existence long ago as a consequence of the theory of general relativity, but up until now we’ve never had a direct observation of them.
A team of researchers from an international collaboration known as LIGO (Laser Interferometry Gravitational-Wave Observatory) seems to have been the first to observe.
Using lasers, LIGO found a subtle stretching and squeezing of spacetime itself was going on. How this happened is actually a remarkably simple concept:
First they shot a laser beam into a tunnel, that got split into two directions:
Here’s an ‘L’ shape to help you imagine the two tunnels it split into.
Next, once both lasers reached the end of their respective tunnels, they bounced back towards the spot where they split so that they could recombine.
A way to think about this is both lasers racing towards the lower-left corner of the ‘L’ again.
Here’s the rub:
Light can be thought of as a wave, with ripples and peaks etc. The waveform of these two laser beams, when combined add into each other.
If the two laser beams have the same wavelength (as they should if there’s no gravitational waves disturbing spacetime) the two split beams will recombine again into the original beam. It looks like this:
If the two laser beams get somehow disturbed and the waves peak on one as the other crests, the resulting combined beam will be that they simply cancel out:
So in the end, if the LIGO researchers detect alterations to their laser when the two beams recombine, they can tell if spacetime’s subtle ripples have morphed the lasers.
The consequences of this discovery are profound.
It, in a sense, opens up the universe to an entire new branch of physics: the universe of gravity.
Ever hear of dark matter? How about dark energy?
These two things are bound to get close scrutiny now as they’re both a part of what’s known as the ‘dark universe’ - basically neither phenomena interact with light (meaning one can’t see them), making it tough to learn much about them.
Yet much of the universe seems to be comprised of these ‘unseeable’ things.
If this discovery holds up, there’s almost certainly a Nobel Prize in the works.
Why? They may have - and I do mean maybe, not did - well…
The folks at LIGO may have just illuminated the 96% of the universe that’s been invisible to our senses for so long. We’ll have to wait and see.
(Image credit: NASA, NSF/LIGO and Brews Ohare respectively)
Because of opposing gravitational forces, if the moon stopped orbiting and fell from the sky, it would only exert a few pounds of pressure on the region including the Earth’s crust, and any human would be able to push it back upward as easily as a balloon.
What if we told you that what you think of as “the present” is actually slightly in the past? Basically, your life isn’t a live feed: It’s a delayed broadcast that your brain is constantly editing and censoring for your convenience.
The delay isn’t much – what’s 80 milliseconds between you and your brain? Nothing, right? Well, a group of neuroscientists disagree. They’ve come up with some freaky time-altering experiments to prove that this difference can change your perspective of cause and effect. For example, in one experiment the volunteers were told to press a button that would cause a light to flash, with a short delay. After 10 or so tries, the volunteers were beginning to see the flash immediately after they pressed the button – their brains had gotten used to the delay and decided to edit it out. Yes, that’s a thing your brain can do.
But that’s not the freaky part. When the scientists removed the delay, the volunteers reported seeing the flash before they pressed the button. Their brains, in trying to reconstruct the events, messed up and switched the order. They were seeing the consequence first and the action second.