Both photons and gravitational waves propagate at the speed of light through the vacuum of empty... [+] space itself. Despite the fact that it isn't intuitive, there's no evidence that there's a physical medium, or aether, required for these entities to travel through.
All throughout the Universe, different types of signals propagate. Some of them, like sound waves, require a medium to travel through. Others, like light or gravitational waves, are perfectly content to traverse the vacuum of space, seemingly defying the need for a medium altogether. Irrespective of how they do it, all of these signals can be detected from the effects they induce when they eventually arrive at their destination. But is it really possible for waves to travel through the vacuum of space itself, without any medium at all to propagate through? That's what Wade Campbell wants to know, asking:
Back in the late 1800s, an "aether" was proposed as the medium that light travels through. We now don't believe that is the case. What is the evidence and/or proof that no aether exists?
It's an easy assumption to make, but a difficult assertion to disprove. Here's the story.
Whether through a medium, like mechanical waves, or in vacuum, like electromagnetic and... [+] gravitational waves, every ripple that propagates has a propagation speed. In no cases is the propagation speed infinite, and in theory, the speed at which gravitational ripples propagate should be the same as the maximum speed in the Universe: the speed of light.
Back in the earliest days of science before Newton, going back hundreds or even thousands of years we only had large-scale, macroscopic phenomena to investigate. The waves we observed came in many different varieties, including:
In the case of all of these waves, matter is involved. That matter provides a medium for these waves to travel through, and as the medium either compresses-and-rarifies in the direction of propagation (a longitudinal wave) or oscillates perpendicular to the direction of propagation (a transverse wave), the signal is transported from one location to another.
This diagram, dating back to Thomas Young's work in the early 1800s, is one of the oldest pictures... [+] that demonstrate both constructive and destructive interference as arising from wave sources originating at two points: A and B. This is a physically identical setup to a double slit experiment, even though it applies just as well to water waves propagated through a tank.
As we began to investigate waves more carefully, a third type began to emerge. In addition to longitudinal and transverse waves, a type of wave where each of the particles involved underwent motion in a circular path a surface wave was discovered. The rippling characteristics of water, which were previously thought to be either longitudinal or transverse waves exclusively, were shown to also contain this surface wave component.
All three of these types of wave are examples of mechanical waves, which is where some type of energy is transported from one location to another through a material, matter-based medium. A wave that travels through a spring, a slinky, water, the Earth, a string, or even the air, all require an impetus for creating some initial displacement from equilibrium, and then the wave carries that energy through a medium towards its destination.
A series of particles moving along circular paths can appear to create a macroscopic illusion of... [+] waves. Similarly, individual water molecules that move in a particular pattern can produce macroscopic water waves, and the gravitational waves we see are likely made out of individual quantum particles that compose them: gravitons.
It makes sense, then, that as we discovered new types of waves, we'd assume they had similar properties to the classes of waves we already knew about. Even before Newton, the aether was the name given to the void of space, where the planets and other celestial objects resided. Tycho Brahe's famous 1588 work,De Mundi Aetherei Recentioribus Phaenomenis, literally translates as "On Recent Phenomena in the Aethereal World."
The aether, it was assumed, was the medium inherent to space that all objects, from comets to planets to starlight itself, traveled through. Whether light was a wave or a corpuscle, though, was a point of contention for many centuries. Newton claimed it was a corpuscle, which Christiaan Huygens, his contemporary, claimed it was a wave. The issue wasn't decided until the 19th century, where experiments with light unambiguously revealed its wave-like nature. (With modern quantum physics, we now know it behaves like a particle also, but its wave-like nature cannot be denied.)
The results of an experiment, showcased using laser light around a spherical object, with the actual... [+] optical data. Note the extraordinary validation of Fresnel's theory's prediction: that a bright, central spot would appear in the shadow cast by the sphere, verifying the absurd prediction of the wave theory of light.
This was further borne out as we began to understand the nature of electricity and magnetism. Experiments that accelerated charged particles not only showed that they were affected by magnetic fields, but that when you bent a charged particle with a magnetic field, it radiated light. Theoretical developments showed that light itself was an electromagnetic wave that propagated at a finite, large, but calculable velocity, today known asc, the speed of light in a vacuum.
If light was an electromagnetic wave, and all waves required a medium to travel through, and as all the heavenly bodies traveled through the medium of space then surely that medium itself, the aether, was the medium that light traveled through. The biggest question remaining, then, was to determine what properties the aether itself possessed.
In Descartes' vision of gravity, there was an aether permeating space, and only the displacement of... [+] matter through it could explain gravitation. This did not lead to an accurate formulation of gravity that matched with observations.
One of the most important points about what the aethercouldn't be was figured out by Maxwell himself, who was the first to derive the electromagnetic nature of light waves. In an 1874 letter to Lewis Campbell, he wrote:
It may also be worth knowing that the aether cannot be molecular. If it were, it would be a gas, and a pint of it would have the same properties as regards heat, etc., as a pint of air, except that it would not be so heavy.
In other words, whatever the aether was or more accurately, whatever it was that electromagnetic waves propagated through it could not have many of the traditional properties that other, matter-based media possessed. It could not be composed of individual particles. It could not contain heat. It could not transfer energy through it. In fact, just about the only thing left that the aether was allowed to do was serve as a background medium through which things like light were permitted to travel.
If you split light into two perpendicular components and bring them back together, they will produce... [+] an interference pattern. If there's a medium that light is traveling through, the interference pattern should depend on how your apparatus is oriented relative to that motion.
All of this led to the most important experiment for detecting the aether: the Michelson-Morley experiment. If aether really were a medium for light to travel through, then the Earth should be passing through the aether as it rotated on its axis and revolved around the Sun. Even though we only revolve at a speed of around 30 km/s, that's a substantial fraction (about 0.01%) of the speed of light.
With a sensitive enough interferometer, if light were a wave traveling through this medium, we should detect a shift in light's interference pattern dependent on the angle the interferometer made with our direction of motion. Michelson alone tried to measure this effect in 1881, but his results were inconclusive. 6 years later, with Morley, they reached sensitivities that were just 1/40th the magnitude of the expected signal. Their experiment, however, yielded a null result; there was no evidence for the aether at all.
The Michelson interferometer (top) showed a negligible shift in light patterns (bottom, solid) as... [+] compared with what was expected if Galilean relativity were true (bottom, dotted). The speed of light was the same no matter which direction the interferometer was oriented, including with, perpendicular to, or against the Earth's motion through space.
Aether enthusiasts contorted themselves in knots attempting to explain this null result.
All of these possibilities, despite their arbitrary constants and parameters, were seriously considered right up until Einstein's relativity came along. Once the realization came about that the laws of physics should be, and in fact were, the same for all observers in all frames of reference, the idea of an "absolute frame of reference," which the aether absolutely was, was no longer necessary or tenable.
If you allow light to come from outside your environment to inside, you can gain information about... [+] the relative velocities and accelerations of the two reference frames. The fact that the laws of physics, the speed of light, and every other observable is independent of your reference frame is strong evidence against the need for an aether.
What all of this means is that the laws of physics don't require the existence of an aether; they work just fine without one. Today, with our modern understanding of not just Special Relativity but also General Relativity which incorporates gravitation we recognize that both electromagnetic waves and gravitational waves don't require any sort of medium to travel through at all. The vacuum of space, devoid of any material entity, is enough all on its own.
This doesn't mean, however, that we've disproven the existence of the aether. All we've proven, and indeed all we're capable of proving, is that if there is an aether, it has no properties that are detectable by any experiment we're capable of performing. It doesn't affect the motion of light or gravitational waves through it, not under any physical circumstances, which is equivalent to stating that everything we observe is consistent with it's non-existence.
Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum.... [+] (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero, and what appears to be the 'ground state' in one region of curved space will look different from the perspective of an observer where the spatial curvature differs. As long as quantum fields are present, this vacuum energy (or a cosmological constant) must be present, too.
If something has no observable, measurable effects on our Universe in any way, shape or form, even in principle, we consider that "thing" to be physically non-existent. But the fact that there's nothing pointing to the existence of the aether doesn't mean we fully understand what empty space, or the quantum vacuum, actually is. In fact, there are a whole slew of unanswered, open questions about exactly that topic plaguing the field today.
Why does empty space still have a non-zero amount of energy dark energy, or a cosmological constant intrinsic to it? If space is discrete at some level, does that imply a preferred frame of reference, where that discrete "size" is maximized under the rules of relativity? Can light or gravitational waves exist without space to travel through, and does that mean there is some type of propagation medium, after all?
As Carl Sagan famously said, "absence of evidence is not evidence of absence." We have no proof that the aether exists, but can never prove the negative: that no aether exists. All we can demonstrate, and have demonstrated, is that if the aether exists, it has no properties that affect the matter and radiation that we do observe.
Visit link:
Ask Ethan: Does The Aether Exist? - Forbes
- NASA-funded pulsed plasma rocket concept aims to send astronauts to Mars in 2 months - Space.com - May 21st, 2024 [May 21st, 2024]
- Ed Dwight, first African American candidate for space travel, takes off 60 years later - ABC News - May 21st, 2024 [May 21st, 2024]
- 90-Year-Old Man Breaks Space Travel Record: 'Everybody Needs to Do This' - Newsweek - May 21st, 2024 [May 21st, 2024]
- Mars in a Flash: How Pulsed Plasma Rockets Are Revolutionizing Space Travel - SciTechDaily - May 21st, 2024 [May 21st, 2024]
- Ed Dwight, the First Black Astronaut Candidate in the U.S., Finally Travels to Space at 90 Years Old - Smithsonian Magazine - May 21st, 2024 [May 21st, 2024]
- Ed Dwight, America's First Black Astronaut Candidate, Makes History by Finally Reaching Space at 90 - Yahoo New Zealand News - May 21st, 2024 [May 21st, 2024]
- After 60 years, the countrys first black astronaut candidate gets to travel to space - Washington Examiner - May 21st, 2024 [May 21st, 2024]
- Meet Ed Dwight, First Black Man Trained As Astronaut To Go To Space After 63 Years - NDTV - May 21st, 2024 [May 21st, 2024]
- The Billionaire Space Race Heats Up With Blue Origin's Latest Launch - Robb Report - May 21st, 2024 [May 21st, 2024]
- Startups have taken big strides this year to bring back space travel - Fortune - February 22nd, 2024 [February 22nd, 2024]
- Isolation and annoying co-workers: Solving the stress of a trip to Mars - Astronomy Magazine - February 22nd, 2024 [February 22nd, 2024]
- SPACE PERSPECTIVE UNVEILS THE FUTURE OF HUMAN SPACE TRAVEL - PR Newswire - February 22nd, 2024 [February 22nd, 2024]
- Space Perspective Unveils The Future Of Human Space Travel - Space Daily - February 22nd, 2024 [February 22nd, 2024]
- Brokaw: 'Constellation' is an unsettling story of space travel - Daily Herald - February 22nd, 2024 [February 22nd, 2024]
- The New Companies Developing Tech on the Space Coast - SpaceCoastDaily.com - February 22nd, 2024 [February 22nd, 2024]
- A space tourism milestone has been reached. Now, testing begins. - Travel Weekly - February 22nd, 2024 [February 22nd, 2024]
- Space Perspective Unveils Test Capsule, Marks Milestone in Titusville's Spaceflight Journey | TalkOfTitusville.com - Talk of Titusville - February 22nd, 2024 [February 22nd, 2024]
- Former West High student now heads tech startup making pharmaceuticals in space - Salt Lake Tribune - February 22nd, 2024 [February 22nd, 2024]
- Space travel: How does it feel to live and work on Mars? - Mint Lounge - February 22nd, 2024 [February 22nd, 2024]
- NASA's Vision for the Future: A New Space Station by 2030 - Medriva - February 22nd, 2024 [February 22nd, 2024]
- How antimatter engines could fly humans to other stars in just a few years - Business Insider Nederland - February 22nd, 2024 [February 22nd, 2024]
- Kam Ghaffarian's Moonshots - The New York Times - February 18th, 2024 [February 18th, 2024]
- Tiny robot's successful first surgery could have huge implications for space travel - ReadWrite - February 18th, 2024 [February 18th, 2024]
- Space Health Challenges and Innovations in Deep Space Travel - Medriva - February 18th, 2024 [February 18th, 2024]
- NASA is Done Setting Fires Inside its Doomed Cargo Spacecraft - Universe Today - February 18th, 2024 [February 18th, 2024]
- 'The Space Race' Review: Why Was NASA So White? - The New York Times - February 18th, 2024 [February 18th, 2024]
- The New Corporate Frontier: Implications of the Space Race on Ground-Based Telescopes and Astronomical Research - Medriva - February 18th, 2024 [February 18th, 2024]
- This Remotely Controlled Robot Will Conduct a Simulated Surgery on the International Space Station - Smithsonian Magazine - February 18th, 2024 [February 18th, 2024]
- Canadian Astronaut Jeremy Hansen: Reflecting on Canada's Role in Space Exploration and Preparing for Artemis II ... - Medriva - February 18th, 2024 [February 18th, 2024]
- Axiom Space's Ax-3 Mission: A Revolutionary Step in Commercial Space Travel - Medriva - January 23rd, 2024 [January 23rd, 2024]
- MBRSC to begin second Mars simulation mission on January 26 - SatelliteProME.com - January 23rd, 2024 [January 23rd, 2024]
- Starfield players outraged over missing space exploration feature - Dexerto - September 3rd, 2023 [September 3rd, 2023]
- This Alternate Method of Space Travel in Starfield is Way More Immersive Than Menus - GameRant - September 3rd, 2023 [September 3rd, 2023]
- Starfield: How to space travel and scan planets - App Trigger - September 3rd, 2023 [September 3rd, 2023]
- Why Do Almost Half of Moon Missions Fail? Here's Why Space Is ... - Inverse - September 3rd, 2023 [September 3rd, 2023]
- Researchers Discover Yet Another Way That Space Travel Kills You - The Debrief - September 3rd, 2023 [September 3rd, 2023]
- Moon landing rekindles interest in space exploration - New Zealand Herald - September 3rd, 2023 [September 3rd, 2023]
- What's it like to win a trip to space? - BBC - September 3rd, 2023 [September 3rd, 2023]
- UNLV Earns NASA Awards to Bolster Space-Related Research ... - UNLV NewsCenter - September 3rd, 2023 [September 3rd, 2023]
- 7 Best Ships To Unlock In Starfield - Screen Rant - September 3rd, 2023 [September 3rd, 2023]
- Starfield players agree that its first dozen hours are its weakest: 'OK ... - PC Gamer - September 3rd, 2023 [September 3rd, 2023]
- Buddhists Do Not Want Space Junk to Fall on Your Head - E-International Relations - September 3rd, 2023 [September 3rd, 2023]
- Will humans ever go to Mars? | Astronomy.com - Astronomy Magazine - September 3rd, 2023 [September 3rd, 2023]
- Unleashing Power of Tether Space Transport - Jammu Kashmir ... - Daily Excelsior - September 3rd, 2023 [September 3rd, 2023]
- Frustrated Starfield players say controversial low review scores are ... - Dexerto - September 3rd, 2023 [September 3rd, 2023]
- Saudi space mission to launch on May 21, first Arab woman astronaut to embark on historic journey to ISS - wknd. - May 18th, 2023 [May 18th, 2023]
- Saudi astronauts to launch space mission on May 21 - Saudi Gazette - May 18th, 2023 [May 18th, 2023]
- First Saudi space mission to launch on May 21 with Kingdoms first astronauts - Al Arabiya English - May 18th, 2023 [May 18th, 2023]
- Flying in space would slash Sydney to London journey time to just two hours - 9News - May 18th, 2023 [May 18th, 2023]
- Flights from Sydney to London take two hours with outer space ... - Innovation News Network - May 18th, 2023 [May 18th, 2023]
- The Final Frontier for the Faithful: Islamic Rulings on Space - E-International Relations - May 18th, 2023 [May 18th, 2023]
- Twitter is still vital for the space community. A former NASA astronaut ... - Space.com - May 18th, 2023 [May 18th, 2023]
- CNL Aims to Better Protect Canadian Astronauts Through New Project Funded by the Canadian Space Agency - Yahoo Finance - May 18th, 2023 [May 18th, 2023]
- SpaceX Announces Seat Reservations For Space Station Travel - Traveling Lifestyle - May 18th, 2023 [May 18th, 2023]
- Axiom-2 Mission Set to Launch with Diverse Crew of Private ... - Transcontinental Times - May 18th, 2023 [May 18th, 2023]
- New Mexico has surreal sand dunes, snowy mountains, space alien ... - Knoxville News Sentinel - May 18th, 2023 [May 18th, 2023]
- To Space and Back: Students Conduct Plant Science Research on ... - ISS National Lab - May 18th, 2023 [May 18th, 2023]
- NASA Tests Robot Snakes to Send to Other Planets - Newsweek - May 18th, 2023 [May 18th, 2023]
- HAL 9000 Is the Most Terrifying Movie A.I. - Collider - May 18th, 2023 [May 18th, 2023]
- Space Travel Market 2023 to 2029 Industry Analysis, Growth ... - Cottonwood Holladay Journal - May 18th, 2023 [May 18th, 2023]
- Virgin Galactic: Revolutionizing Space Travel and the Future of ... - Best Stocks - May 18th, 2023 [May 18th, 2023]
- Virgin Galactics first private space tourism flight to take off in June - Travel Tomorrow - May 18th, 2023 [May 18th, 2023]
- NASA PC-12 to conduct aerial flights over Cleveland roadways - AviationSource News - May 18th, 2023 [May 18th, 2023]
- Florida's 'Space Coast' Has Incredible Beaches, Food, and Dolphins Here's How to Plan a Trip - Yahoo Life - May 18th, 2023 [May 18th, 2023]
- Fast X adds Jason Momoa to the Vin Diesel-driven franchise for the first instalment of a series finale that already feels like its spinning its wheels... - May 18th, 2023 [May 18th, 2023]
- Airstreams new travel trailer fits a swanky studio apartment into less than 17 feet of living space - The Manual - May 18th, 2023 [May 18th, 2023]
- Steven Wright, Master of the One-Liner, Tries His Hand at a Novel - The New York Times - May 18th, 2023 [May 18th, 2023]
- Poop falling from the sky: Here's how often that happens - CBS News - May 18th, 2023 [May 18th, 2023]
- How will we react when the aliens arrive? - The Irish Times - May 18th, 2023 [May 18th, 2023]
- Luxury stores with the most beautiful interiors - Luxebook - May 18th, 2023 [May 18th, 2023]
- Is it really possible to travel back in time? - BBC Sky at Night Magazine - May 18th, 2023 [May 18th, 2023]
- The pros and cons of space colonization - Yahoo News - May 10th, 2023 [May 10th, 2023]
- In space, failure is an option often the only one - Nature.com - May 10th, 2023 [May 10th, 2023]
- Virgin Galactic Announces Return to Space, Crew | - Santa Fe Reporter - May 10th, 2023 [May 10th, 2023]
- A tour inside the Thailand's first space themed hotel - Manila Bulletin - May 10th, 2023 [May 10th, 2023]
- Buzz Aldrin named Brigadier General by Space Force - We Are The Mighty - May 10th, 2023 [May 10th, 2023]
- Virgin Orbit Failure Casts Cloud Over Space Voyages - Kiplinger's Personal Finance - May 10th, 2023 [May 10th, 2023]
- OPINION: A Return to Profitability for Commercial Aviation - Avionics ... - Aviation Today - May 10th, 2023 [May 10th, 2023]
- 12 Realistic Films About Space Travel and Making Contact With Aliens - Wealth Of Geeks - May 10th, 2023 [May 10th, 2023]
- Dont be fooled: 10 of the biggest travel myths, busted - Sydney Morning Herald - May 10th, 2023 [May 10th, 2023]