Sound can travel through space, contrary to popular belief. However, to explain why this is, we need to start first by asking what sound is.
What is sound?
We are surrounded by sounds from the moment we are born until we breathe our last breath. However, few people ever really ask what sound is.
The University of Toronto
defines sound as being:
“Sound is a pressure wave which is created by a vibrating object.”
If we look at this definition, it is apparent that we need two things to make sound possible. We need a pressure wave, and we need a vibrating object. The pressure wave comes from whatever is creating the sound. A tiny baby’s cries will generate pressure waves, in the same way that a drill used at a construction site creates pressure waves.
These pressure waves send vibrations through a medium, and that creates sound. The medium is the transporting solution to hearing sound. Most often, our medium for sound is air.
The tiny baby’s cries will vibrate through the air, sending pressure waves that are picked up by our ears. Likewise, the construction drill sends vibrations through the air, which our ears pick up.
The vibration particles move similarly to the movements of a wave, and they are called longitudinal waves. These longitudinal waves create compressions and rarefactions within the air.
Amplitude and Volume
The amount of work needed to generate the motion energy of the vibration particles is measured by the amplitude of a sound. Amplitude is a wave’s maximum variation in air pressure.
So, what is the relationship between volume and amplitude?
That’s a complicated question. The relationship between the measured amplitude of a sound, and our impression of how loud it is, is very complex and depends on many factors.
Not to mention that loudness is subjective, meaning that what I would consider loud, you might not. The relative loudness of two sounds is related to the ratio of their intensities.
Now let’s discuss this in more detail. If a sound has twice as great an amplitude, does it sound twice as loud to us? Generally, the answer is no. This is because of the following reasons:
- Our subjective sense of how loud a sound is is not directly proportional to amplitude.
- Our sense of how loud a sound varies greatly depending on the frequency of the sounds.
So even though there is a correlation between amplitude and volume, it is not perfectly linear. This is because our ears can perceive a vast range of sound pressure.
According to the Environmental Protection Department of Hong Kong, “The softest sound a normal human ear can detect has a pressure variation of 20 micro-Pascals, abbreviated as µPa, which is 20 x 10-6 Pa (“20 millionth of a Pascal”) and is called the Threshold of Hearing.” That softest sound has about a millionth amplitude in comparison to the loudest sound we can hear.
Since discussing amplitude with such a vast range of 0 to one million, it makes sense to compare amplitudes on a logarithmic scale. Therefore, decibels are commonly used to compare the ratio between two amplitudes, and it is abbreviated as dB.
Can Sound Travel Through Space?
The 1979 hit movie, Alien, had a tagline, “In Space, no one can hear your scream.” That fit the movie’s plot perfectly as it created a more intense atmosphere for viewers. Is it correct, though? It seems that in certain circumstances, sound can be bounced between objects in a vacuum after all, which would mean that there are possibilities where you could hear someone scream in space. As mentioned earlier, sound waves travel vibrations of particles in mediums such as air, water, or metal. Therefore, it makes sense to assume that the sound waves can’t travel through space since there are no atoms or molecules to vibrate.
In space, where there aren’t many particles that can vibrate and create the conventional sound waves we know on Earth. Even if there were regular sound waves in space, they would be influenced by other elements in space such as solar flares, supernovae, black hole mergers, and other cosmic catastrophes. The lack of space particles has led scientists to believe that sound can’t travel through space for centuries. However, due to LIGO’s first positive detection result, we have discovered another type of compression-and-rarefaction that only requires the fabric of space itself to travel through, which are gravitational waves. This incredible breakthrough makes it possible for us to hear the Universe for the first time in the history of humankind.
What is the LIGO Project?
LIGO (“The Laser Interferometer Gravitational-Wave Observatory”) is a project searching for distortions in space-time that could indicate the passage of gravitational waves.
What is the purpose of the LIGO Project?
The LIGO Project’s mission is to detect gravitational waves from some of the most violent and energetic processes in the Universe. The data LIGO collects has phenomenal effects on many areas of physics. These areas include gravitation, relativity, astrophysics, cosmology, particle physics, and nuclear physics.
How does LIGO work?
In space, the gravitational waves cause space to stretch in one direction while simultaneously compressing in a vertical direction. In LIGO, the result is one arm of the interferometer gets longer while the other gets shorter. Then it happens vice versa and keeps happening back and forth as long as the wave is passing.
Who funds LIGO?
It is undeniable that LIGO has unmeasurable advantages for the human race and unimaginable costs, and we can’t help but wonder who picks up the bill. NSF(National Science Foundation) funds LIGO, while it is operated jointly by Caltech and MIT.
Understanding Gravitational waves
According to General Relativity, Gravitational waves had to exist for our theory of gravity to be consistent. It is in complete contrast to Newton’s gravity, where any two masses orbiting one another would remain in that configuration forever. Einstein’s theory of gravity was to conserve energy; energy must be carried away in the form of gravitational waves. These waves are fragile, and their effects on the objects in space-time would be next to zero.
However, if you know how to listen for them in the same way the components of a radio understand how to listen for long-frequency light waves, you can not only detect these signals but hear them just as you would hear any other sound. Amplitude and frequency waves are no different from any other wave. General Relativity makes bold predictions for what these waves could sound like, with the most prominent wave-generating signals are the easiest ones to detect. What sound would create the largest amplitude in space? It would be the spiral of two black holes into each other.
LIGO’s first event
Just a few days after advanced LIGO began collecting data for the first time, in September of 2015, a massive, suspicious signal was detected. It came as a surprise because it would have carried so much energy in a 200-millisecond burst that it would have outshone all the stars in the observable universe combined, and yet that signal turned out to be robust. The energy from that burst was created by two black holes of different masses, 36 and 29 solar masses, merging into a single 62 solar mass. If you are doing the math, you’d realize that 36 + 29 doesn’t equal 62. So, you might wonder where the missing three solar masses disappeared to. Instead, they were converted into pure energy resulting in gravitational waves rippling through space. That was LIGO’s first event ever detected.
Now, a few years later, LIGO is still a very successful project. Not only have black holes merging with other black holes been detected, but the future of gravitational wave astronomy is exciting and healthy, with new detectors opening up our ears to new types of sounds. LISA(The Laser Interferometer Space Antenna), space interferometers will make it possible to hear even lower frequency sounds because of longer baselines. These will include sounds like neutron star mergers, feasting super large black holes, and unifications with vastly unequal masses. LISA uses pulsar timing arrays that can measure even lower frequencies. Combining new techniques will assist humanity in our quest for the oldest gravitational waves of all. We might be able to not only detect but even hear the ancient waves predicted by cosmic inflation dating all the way back to the beginning of our Universe.
6 facts about gravitational waves that are out of this world
1. Gravitational waves are actually just ripples in space-time
Einstein’s theory of General Relativity concluded that gravity is not a force reaching out through the universe, but instead, it’s a purely bending of space-time. Thus, when an object accelerates, it changes the space-time around it. The result is that distortion traveling away from the source at the speed of light.
2. Insanely heavy objects create gravitational waves.
Now, when we say insanely heavy, just how much weight are we talking about? The first proof that gravitational waves exist came from a binary pulsar, two neutron stars that weighed about the Sun’s mass, that orbited each other. The pulsars are losing energy because the pulsar’s orbit is slowly becoming smaller. That energy is precisely the amount predicted by general relativity that the pulsars would give off in gravitational waves.
3. The effect of gravitational waves is minuscule.
Since gravitational waves are simply ripples in space-time, they cause the distance between two points to alter slightly.
4. Measuring gravitational waves is exceptionally complicated.
Detecting a change in the distance much smaller than the proton requires excellent precision. Therefore, each LIGO installation is a laser interferometer that is made up of two underground pipes. Each of these pipers is 1.3 meters wide and 4 km long and set in an L-shape. The pipes’ inside is a vacuum. Therefore, when a gravitational wave passes through LIGO, one instrument’s arm gets longer, and the other gets shorter. As a result, a laser beam is then split in half and sent down the two pipes.
After that, it is reflected, and then it gets recombined, so the two beams cancel each other out in a destructive interference if no gravitational wave is present. However, if there is a gravitational wave, the beams will not be canceling each other out. To detect a gravitational wave, the rays are bounced between the two arms about 400 times, that that the light travels a distance of 1,600 km.
5. LIGO is extremely sensitive
LIGO detects such a slight change in distance that it can detect many other vibrations, too. Gravity gradient noise is one source of noise that changes Earth’s gravitational field when a pulse passes through the ground close to the mirrors. These mirrors that reflect the light weigh 40 kg and hang by silica fibers in a suspension system. To ensure that LIGO detects gravitational waves and not just passing cars, there are two LIGO installations—one is stationed in Louisiana, and the other in Washington. A gravitational wave shows up at both structures.
6. Gravitational Wave astronomy can show us a whole new side to the Universe.
If supermassive black holes merged in a faraway galaxy, it could be observed by LIGO. Scientists also expect that if a neutron star is non-spherical, the gravitational waves could be observed, thereby revealing much about the star’s structure. Being able to look at the Universe in a new way shows astronomers something that wasn’t expected. Therefore, gravitational wave astronomy will most likely show us something we haven’t even thought of. That is a fascinating prospect, not just for scientists but for the whole human race.
Conclusion
New technology on Earth and in space has shown us that there’s so much to hear that it is clear that we’ve only just started listening for the first time. A universe of sounds is ready to be explored.