The fabric of expanding space means that the farther away a galaxy is, the faster it appears to... [+] recede from us. However, that doesn't mean that galaxies are actually moving through the Universe at speeds faster than light; the fabric of space itself is continuously changing in properties.
One of the fundamental rules we all learn in physics set forth by Einstein more than 100 years ago is that there's an ultimate speed limit that everything in the Universe must obey: the speed of light. That fundamental speed, 299,792,458 m/s, is the speed at which all massless particles must travel through the vacuum of space. If you have mass, you can only approach (but never reach) that speed; if you travel through a medium instead of a vacuum, you can only travel slower than that ultimate cosmic limit. But if that's true, then how come we can see objects in our Universe, which began with a Big Bang some 13.8 billion years ago, that are up to 46 billion light-years away? That's at the heart of Robert Lipinski's question, which asks:
Why does the fabric of space-and-time expand faster than the speed of light?
It's one of the most difficult concepts in all of physics to understand, but we're up to the challenge. Let's find out.
One revolutionary aspect of relativistic motion, put forth by Einstein but previously built up by... [+] Lorentz, Fitzgerald, and others, that rapidly moving objects appeared to contract in space and dilate in time. The faster you move relative to someone at rest, the greater your lengths appear to be contracted, while the more time appears to dilate for the outside world. This picture, of relativistic mechanics, replaced the old Newtonian view of classical mechanics, but also carries tremendous implications for theories that aren't relativistically invariant, like Newtonian gravity.
When Einstein put forth the notion of Special Relativity in 1905, it was as straightforward as it was revolutionary. It began by considering a phenomenon we've all interacted with: a light wave. For many decades, Einstein and his contemporary had known that light is an electromagnetic wave: an energy-carrying wave with oscillating, in-phase electric and magnetic fields. And, in a vacuum, it always moved at the same speed: the speed of light.
This last part was the most troubling to scientists. If you were on a train moving at 100 miles-per-hour (161 km/hr) and you threw a baseball at 100 miles-per-hour (161 km/hr) in the forward direction, that ball would move at 200 miles-per-hour (322 km/hr) from the perspective of someone on solid ground. But light didn't work that way; it always moves at the same speed through the vacuum of empty space, from every perspective imaginable.
If the arm lengths are the same and the speed along both arms is the same, then anything traveling... [+] in both of the perpendicular directions will arrive at the same time. But if there's an effective headwind/tailwind in one direction over the other, or the arm lengths change relative to one another, there will be a lag in the arrival times.
This was demonstrated to great precision in the 1880s by scientist Albert Michelson and his assistant, Edward Morley. In their experiment, they took a beam of coherent light (of the same wavelength) and passed it through a beam splitter: a device that splits the light into two perpendicular components. The light then travels down both paths of identical lengths until it strikes a mirror, reflects back, and gets recombined to create an interference pattern.
Now, here's the key point: if one path is shorter than the other, or if the light moves faster (or slower) in one direction than the other, the interference pattern will shift. This happens to enormous precision in the LIGO and Virgo gravitational wave detectors, where passing gravitational waves change the path length of the two different directions. But, even with the motion of the Earth relative to the Sun at ~30 km/s, the interference pattern seen in the Michelson-Morley experiment never changed.
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.
This taught us something incredibly important: the velocity of light is independent of any relative motion through space. No matter who you are, where you are, how quickly or in what direction you travel through the Universe, you will always observe all light waves traveling through space at that same universal speed limit: the speed of light in a vacuum. If you and the source move away from one another, the light's wavelength gets redshifted; if you mutually move towards one another, the wavelength gets blueshifted. But the speed of light itself never changes through the vacuum of space.
This idea was revolutionary when Einstein proposed it, with many professional physicists (wrongfully) resisting it for decades. The opposition made it no less true, however. But the big prize still remained: to incorporate gravitation into the equation.
Countless scientific tests of Einstein's general theory of relativity have been performed,... [+] subjecting the idea to some of the most stringent constraints ever obtained by humanity. The presence of matter and energy in space tells spacetime how to curve, and that curved spacetime tells matter and energy how to move.
Before Einstein, gravitation was a Newtonian phenomenon. According to Newton, space and time were absolute, rather than relative, entities. The gravitational force of attraction between any two masses had to propagate infinitely fast, rather than limited by the speed of light.
The bigger revolution that Einstein brought to physics was the overthrow of this picture of gravitation. Sure, you could use Newtonian gravity as a very good approximation for almost all conditions, but in situations where matter or energy passed close to a large mass, Newton wouldn't give you the correct answers.
Mercury's orbit precessed more than Newton predicted. Light passing close to the Sun during an eclipse bent by a greater amount than Newton could explain.
The results of the 1919 Eddington expedition showed, conclusively, that the General theory of... [+] Relativity described the bending of starlight around massive objects, overthrowing the Newtonian picture. This was the first observational confirmation of Einstein's General Relativity, and appears to align with the 'bent-fabric-of-space' visualization.
As the evidence clearly showed, Einstein's General Relativity where mass and energy curved space and that curved space determined the motion of mass and energy had superseded Newtonian gravity. This new conceptualization of gravitation and of the fabric of space-and-time itself brought another revelation along with it: the fact that the fabric of the Universe, if it was full of roughly equal amounts of matter and energy everywhere, could not be static and unchanging.
Instead, as observationsas early as the 1920s began to definitively show, there was a systematic relationship between an object's distance from us and the amount that its light was observed to redshift. Sure, galaxies move through space relative to one another, but only at speeds up to a few thousand km/s. Yet when we view the actual redshifts of distant galaxies, they correspond to recession speeds much, much greater than those values.
The distance/redshift relation, including the most distant objects of all, seen from their type Ia... [+] supernovae. The data strongly favors an accelerating Universe. Note how the y-axis includes speeds that exceed the speed of light, but this doesn't tell the full story about what's actually going on with the expanding Universe.
The reason we're seeing these cosmic redshifts scale with distance, as scientists quickly came to realize, is because the fabric of the Universe itself is expanding. Just like raisins in a leavening loaf of raisin bread dough, the every galaxy in the Universe all see the other galaxies moving away from them, with the more distant raisins (or galaxies) appearing to move away at faster rates.
But why is this?
It isn't because the raisins are moving relative to the dough that they're embedded in, nor is it because the individual galaxies are moving through the fabric of space. Rather, it's owing to the fact that the dough itself just like the fabric of space itself is expanding, and the raisins (or galaxies) are just along for the ride.
The 'raisin bread' model of the expanding Universe, where relative distances increase as the space... [+] (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what's been known all the way back since the 1920s.
Meanwhile, because these objects are galaxies, they're filled with light-emitting stars. They emit light continuously from the moment they first turn on, but we can only observe them from the moment that light first arrives at our eyes after journeying through the Universe.
Not the Newtonian Universe, mind you: the expanding, Einsteinian one.
This means that there are galaxies out there whose light is only just now arriving here on Earth for the first time, after journeying through the Universe for more than 13 billion years. The first stars and galaxies formed just a few hundred million years after the Big Bang, and we've discovered galaxies from as far back as when the Universe was just 3% of its present age. And yet, that light has been so severely redshifted by the expanding Universe that the light was ultraviolet when it was emitted, but is already far into the infrared by the time we can observe it.
This simplified animation shows how light redshifts and how distances between unbound objects change... [+] over time in the expanding Universe. Note that the objects start off closer than the amount of time it takes light to travel between them, the light redshifts due to the expansion of space, and the two galaxies wind up much farther apart than the light-travel path taken by the photon exchanged between them.
If we were to ask, from our perspective, what this means for the speed of this distant galaxy that we're only now observing, we'd conclude that this galaxy is receding from us well in excess of the speed of light. But in reality, not only is that galaxy not moving through the Universe at a relativistically impossible speed, but it's hardly moving at all! Instead of speeds exceeding 299,792 km/s (the speed of light in a vacuum), these galaxies are only moving through space at ~2% the speed of light or less.
But space itself is expanding, and that accounts for the overwhelming majority of the redshift we see. And space doesn't expand at a speed; it expands at a speed-per-unit-distance: a very different kind of rate. When you see numbers like 67 km/s/Mpc or 73 km/s/Mpc (the two most common values that cosmologists measure), these are speeds (km/s) per unit distance (Mpc, or about 3.3 million light-years).
The restriction that "nothing can move faster than light" only applies to the motion of objects through space. The rate at which space itself expands this speed-per-unit-distance has no physical bounds on its upper limit.
The size of our visible Universe (yellow), along with the amount we can reach (magenta). The limit... [+] of the visible Universe is 46.1 billion light-years, as that's the limit of how far away an object that emitted light that would just be reaching us today would be after expanding away from us for 13.8 billion years. However, beyond about 18 billion light-years, we can never access a galaxy even if we traveled towards it at the speed of light.
It might seem strange to consider all that this implies. Because we have dark energy, the expansion rate will never drop to zero; it will remain at a positive, finite value. It means that even though only 13.8 billion years have passed since the Big Bang, we can observe light from objects that are already 46.1 billion light-years away. And it means that beyond a fraction of that distance about 18 billion light-years no object launched today from Earthcould ever reach it.
But no object is actually moving through the Universe faster than the speed of light. The Universe is expanding, but the expansion doesn't have a speed; it has a speed-per-unit-distance, which is equivalent to a frequency, or an inverse time. One of the most surprising facts about the Universe is that if you do the conversions and take the inverse of the expansion rate, you can calculate the "time" that you get out.
The answer? Approximately 13.8 billion years: the age of the Universe. There isn't a fundamental reason for that fact; it's just a fascinating cosmic coincidence.
- Watch the Virgin Galactic Spaceship Soar at the Edge of Space - Robb Report - May 24th, 2021
- Travelling Through a Wormhole in Space May Be Possible, New Research Suggests - Gadgets 360 - May 24th, 2021
- As Interest In Space Tourism Booms, New Research Shows What May Happen To The Body In Space - Forbes - May 24th, 2021
- Space exploration China lands a rover on Mars - The Economist - May 24th, 2021
- A Serene Shore Resort, Except for the SpaceX Ball of Fire - The New York Times - May 24th, 2021
- ETF Battles: Want to Invest in Space Travel and Exploration? Try these 3 ETFs - TheStreet - May 24th, 2021
- Stronger together: Moving from space exploration to nuclear utilities - Modern Diplomacy - May 24th, 2021
- The ARKX ETF: Investing in the Final Frontier - ETF Trends - May 24th, 2021
- Heres how NASA will search for water on the Moon - Yahoo Entertainment - May 24th, 2021
- What We Know About Chinas Mars Rover Zhurong Landing - The New York Times - May 24th, 2021
- China says Martian rover takes first drive on surface of Red Planet - Reuters - May 24th, 2021
- An aspiring Irish astronaut is currently on a simulated moon mission - Siliconrepublic.com - May 24th, 2021
- To the moon...literally: Should you buy into the future of space travel? - Global Banking And Finance Review - May 24th, 2021
- SpaceX's dearMoon mission has pitted two brothers against each other. One of the siblings said he was shocked - Business Insider India - May 24th, 2021
- Virgin Galactic Shares Rocket Higher: What Investors Should Know - Benzinga - May 24th, 2021
- Warp Drives and Negative Energy: Physicists Give Chances of Faster-Than-Light Space Travel a Boost - SciTechDaily - May 18th, 2021
- LSU student from Zachary provide work that will make NASA mission to moon in 2022 - The Advocate - May 18th, 2021
- Connecting the Dots of History: Recognizing an Oklahoman's contribution to the U.S. space program - Oklahoman.com - May 18th, 2021
- The $10 billion Space telescope that will help us travel back in time - Euronews - May 18th, 2021
- Helen Sharman: Thirty years since first Briton went to space - BBC News - May 18th, 2021
- A Florida Kayak Excursion That's Like Paddling through the Milky Way - Red Tr... - Red Tricycle - May 18th, 2021
- SpaceX Files Paperwork for First Spaceship Orbital Flight: Texas to Hawaii - Weatherboy - May 18th, 2021
- Malachy Clerkin: Sport is all about fun - like hitting a golf ball on the moon - The Irish Times - May 18th, 2021
- If Earth falls, will interstellar space travel be our salvation? - Yahoo News - May 16th, 2021
- Not just Earth, humans are polluting space too. Heres how we can stop - ThePrint - May 16th, 2021
- OPINION: SpaceX is making history The Appalachian - The Appalachian Online - May 16th, 2021
- Air and Space Museum in Spotlight as X-wing Exhibition Announced - The Great Courses Daily News - May 16th, 2021
- US Intel Chief: Chinese Space Station is a Threat to National Security - Futurism - May 16th, 2021
- Warp drives: Physicists give chances of faster-than-light space travel a boost - EarthSky - May 11th, 2021
- First American In Space: The Flight of Alan B. Shepard - National Air and Space Museum - May 11th, 2021
- The second Israeli in space: "I'm aware of the risks, but not afraid of the dangers" - Geektime - May 11th, 2021
- Star Wars X-Wing Starfighter Lands at the National Air and Space Museum - Smithsonian Magazine - May 11th, 2021
- Want to become a space tourist? You finally can if you have $250,000 and a will to sign your life away - The Conversation AU - May 11th, 2021
- Space tourism is here 20 years after the first stellar tourist, Jeff Bezos' Blue Origin plans to send civilians to space - The Conversation US - May 9th, 2021
- Southwestern to explore the health effects of space travel at the next Physics and Astronomy Lecture - Coos Bay World - May 9th, 2021
- Israeli Mission to Test Tech for Next Generation of Space Travel - Bloomberg - May 9th, 2021
- A bottle of wine aged in space could sell for $1 million how and why it tastes different than Earth-bound wine - CNBC - May 9th, 2021
- Bringing sci-fi concepts to real space exploration | Stanford News - Stanford University News - May 9th, 2021
- #SpaceWatchGL Opinion: Five reasons why astronomy is important to our future in space. - SpaceWatch.Global - May 9th, 2021
- Veteran NASA Astronaut Jeff Williams talks about the future of space travel, Mars, and a Woman on the Moon - CW39 - May 9th, 2021
- Smithsonian Will Display Star Wars X-Wing Fighter - The New York Times - May 9th, 2021
- NASAs Defunct Space Runway Will Be Used By a New Spaceplane in 2022 - Observer - May 9th, 2021
- 60 years ago, Alan Shepard became the first American in space | US Embassy & Consulates in Italy - US Embassy Rome - May 9th, 2021
- 44 Israeli Research Projects Headed For Space On Rakia Mission - NoCamels - Israeli Innovation News - May 9th, 2021
- Elon Musk is right about the inevitable risks and rewards of space travel - The Independent - May 9th, 2021
- Breaking News - discovery+ Documents Backyard Engineers Pursuing Their Dreams of Space Flight in All-New Limited Series "Homemade... - May 1st, 2021
- The Food Tech Show: The Future of Space Food - The Spoon - May 1st, 2021
- Light This Candle: What You Need to Know About Alan Shepard's Historic Spaceflight - National Air and Space Museum - May 1st, 2021
- Virgin Galactic Reschedules First Quarter 2021 Financial Results and Conference Call In Response to Recent SEC Guidance Relating to Warrants Issued by... - May 1st, 2021
- Mars helicopter Ingenuity snaps epic photo of rover tracks, will attempt 3rd flight Sunday - Space.com - May 1st, 2021
- Stanford alumna Kate Rubins returns to Earth after six months of being in space - The Stanford Daily - May 1st, 2021
- Space Tourism 20 Years in the Making Is Finally Ready for Launch - Nextgov - April 29th, 2021
- Warp drives: Physicists give chances of faster-than-light space travel a boost - The Conversation US - April 29th, 2021
- New warp drive research dashes faster than light travel dreams, but reveals stranger possibilities - Space.com - April 29th, 2021
- NASA's Mars helicopter Ingenuity will attempt its boldest flight yet today - Space.com - April 29th, 2021
- Space tourism is now a reality if youre filthy rich - The Next Web - April 29th, 2021
- Its theoretically possible to travel faster than light using the warp drives seen in Star Trek - Scroll.in - April 29th, 2021
- The explanation behind warp speed Popular Science - Popular Science - April 29th, 2021
- Meet the startup reaching for the moon to make oxygen - ISRAEL21c - April 29th, 2021
- Experts Study People Working in Antarctica As a Proxy for Astronauts - Business Insider - April 29th, 2021
- Successful carbon dioxide into oxygen conversion 'is the key' to space travel - Sky News Australia - April 29th, 2021
- Hypersonix joins the space race with hydrogen fuel - H2 View - April 21st, 2021
- So a helicopter flew on Mars for the first time. A space physicist explains why that's such a big deal - The Mandarin - April 21st, 2021
- Space Travel Reality Show Partnered With NASA, Featured On Colbert - Forbes - April 19th, 2021
- NASA chooses SpaceX to land next astronauts on the Moon Spaceflight Now - Spaceflight Now - April 19th, 2021
- Intriguing Warp Drive Research Dashes Faster Than Light Travel Dreams But Reveals Stranger Possibilities - SciTechDaily - April 19th, 2021
- Everett's own spaceman thrilled to join all-civilian mission | HeraldNet.com - The Daily Herald - April 19th, 2021
- Sitting in a tin can: why sci-fi films are finally telling astronaut life like it is - The Guardian - April 19th, 2021
- New warp drive research dashes faster than light travel dreams but reveals stranger possibilities - The Conversation AU - April 19th, 2021
- New Warp Drive Research Dashes Faster-Than-Light Travel Dreamsbut Reveals Stranger Possibilities - Singularity Hub - April 19th, 2021
- NASA Astronaut Kate Rubins and Crewmates Return From ISS After 185 Days in Space - autoevolution - April 19th, 2021
- I Watched the First Space Shuttle Flight 40 Years Ago | Flagpole - Flagpole Magazine - April 19th, 2021
- The new trailer for Fast 9 teases space travel, a cameo from Paul Walker, and more! - News24 - April 19th, 2021
- Is SpaceX Really Worth $74 Billion? Forbes - Forbes - April 19th, 2021
- Travel deep into the forest with the "Queen of the Forest Canopy" and out into space with the first woman of color in space - fox13now.com - April 19th, 2021
- Comments on: A new step in the space race: China travels to the stars - Commentary Box Sports - April 19th, 2021
- Erik Lindbergh: Right Now is the 'Most Exciting Time' in Aviation - ERAU News - April 19th, 2021
- It looks like the busiest season ever for campsites but there should be space for everyone - Telegraph.co.uk - April 19th, 2021
- Virgin Galactics Mirror-Like Spaceship Brings Us One Step Closer to Space Travel - Robb Report - March 31st, 2021
- An Astronaut's Heart Shrank From Space Travel, Study Finds - The New York Times - March 31st, 2021