We’re familiar with the sky on Tatooine with its twin suns. But could a planet actually orbit two stars at the same time? Could you have a planet in a multiple star system with 4, 6 or more suns?
Hey kids, you remember Star Wars right? Tatooine ring any bells? Lots of sand Tusken raiders walking single file. Banthas sweating all over the place like some crazy mammoth-goat breeding experiment gone horribly awry?
Tatooine was an arid desert planet, it had 2 suns and 3 moons. It’s not the only fictional planet to orbit multiple suns. In Nightfall by Isaac Asimov, planet Lagash had 6 suns. Could something like this be possible?
Interestingly, most stars in the Milky Way are in multiple star systems. You can easily have double, triple, or quadruple systems. There are even star clusters with hundreds or even thousands of stars. Just imagine the crazy chaotic gravitational interactions in a multiple star system.
So, could they have planets? Yes. There are circumbinary systems, where stars orbit each other their planets orbit outside, circling them both. Since the stars orbit one another so closely, it’s the gravitational equivalent of a single star. From an orbiting planet, the stars would always appear together in the sky.
To date, we have discovered 17 of these systems. Then there are wide binary systems, which are far more dangerous for planets. Here the planets orbit one main star, and there’s another star which maintains a distant orbit much further out. You don’t want to live there. The gravitational interactions are chaotic and lead to mayhem. In simulations, planets which aren’t tightly orbiting a star are ejected out of the system, or crashed into other planets or stars.
Artist’s impression of the Cygnus-X1 binary. Credit: NASA / Honeywell Max-Q Digital Group / Dana Berry
We might already be detecting highly elliptical orbits from disrupted planets just like these. A triple star system was recently discovered in the constellation Cygnus: HD 188753. Here, a pair of stars are tightly bound, and these are in a wide binary arrangement with a sun-mass star. A planet closely orbits the primary star, but all other planets were likely ejected.
In the year 2012, a planet was found around Alpha Centauri B, and PH1 was the first quadruple star system to be discovered to have a planet. Kepler 47 is a multi-star, multi-planet system. Two stars orbit one another every 7.45 days. Here, the gas giant Kepler 47c orbits the stars every 303 days and is even located in the habitable zone. This sounds like perfect concept art for a Vin Diesel film, or artwork airbrushed on the side of a van.
Kepler-16b is but one example of an uncanny world. It orbits two suns. Credit: Discovery
Finally, In 2011, the Kepler-16 system was found to have a circumbinary planet in the habitable zone. So, two stars, closely orbiting each other and a Saturn-mass, Kepler 16b orbiting the two. Astronomers informally called this a real Tatooine.
What do you think? Would you want to live on a desert world like Tatooine or Arrakis? Tell us your thoughts in the comments below.
It feels like you just can’t get away from clingy gravity. Even separated by distances of hundreds of millions of light years, gravity is reaching out to all of us. Is there a place you could go to get away from gravity entirely?
Fortunately for our space intolerant tissues and terrible oxygen dependency withdrawal symptoms, gravity binds us to our sweet, cozy home with breathable air, the Earth. Its collective mass is trying to accelerate you towards its center, that way, at 9.8 meters per second squared. But the Earth isn’t the only one looking to cuddle.
You’re also being pulled at by the Moon, and if it weren’t for the Earth here, that pull could hurl you far off into deep space, or crash you into its cold dusty surface. In fact, as the Moon passes overhead, you’re being imperceptibly tugged upwards. This possessive tug o war isn’t just between the moon, and the earth fighting over you like an older brother keeping a small doll out of reach a younger sibling.
The Sun is also in on this shenanigan. Gravity from there is pulling at you from a distance of 150 million km. Well, aren’t we popular. So how far would you have to go to escape this gravitational custody battle completely?
Even At 2.5 million light years distance, gravity is still reaching out and being a clingy creeper. The Milky Way and Andromeda are pulling towards each other. The gravity between these two bodies is strong enough to overcome the expansion of the universe. Which will result in a galactic smash-up derby a few billion years from now.
There’s no end to it. Gravity appears to be madly greedy and long armed. Members of the Virgo Super cluster are connected to each other, and they’re dozens of millions of light-years apart. Objects in the Pisces-Cetus Super cluster complex are even connected to each other by our invisible and obnoxiously possessive friend. And they are hundreds of millions of light years apart…
In fact, you’re so popular that you are gravitationally pulled towards even most distant object in the observable Universe. And they, in turn, are linked to you. As a result, without the outward expansion and acceleration of the Universe, everything would fall inward to a common center of gravity. Newton thought that gravity was instantaneous and if the Sun disappeared, the Earth would immediately fly away. Einstein realized that gravity is distortions of spacetime caused by mass. And as it turns out, gravity moves at the speed of light.
Artist’s impression of gravitational waves. Image credit: NASA
If the Sun disappeared, Earth would continue to follow the curved spacetime distortion for 8 whole minutes. Interactions between massive objects, like when black holes collide, cause ripples in spacetime called gravitational waves. As a gravitational wave passes through, you get warped in spacetime, like a wave in the water. The amount is so slight we’ve never seen them directly. However, the decay of pulsar orbits have shown them indirectly.
The ground-based LIGO experiment might someday detect a gravitational wave, but there’s been no luck so far. The Space-based LISA experiment should detect gravitational waves with more precision. The first version will launch in 2015, but the real experiment probably won’t be operational until 2030.
Everybody wants a piece, and I don’t know about you, I just want to be left alone. Gravity’s is reach is amazingly far. It’s everywhere, all the time, and it’s having none of that. What do you think? If you had the power to remove yourself from Gravity’s pull, what would you do? Tell us in the comments below.
Image of the Andromeda Galaxy, showing Messier 32 to the lower left, which is currently merging with Andromeda. Credit: Wikipedia Commons/Torben Hansen
In a Universe that’s expanding apart, isn’t it strange that Andromeda is actually drifting towards us? Dr. Thad Szabo from Cerritos College explains why this is happening.
“I’m Thad Szabo, and I teach astronomy and physics at Cerritos College.”
Is Andromeda drifting towards us?
“The reason that we see Andromeda moving toward us is because it’s nearby enough, and the Milky Way is massive enough and Andromeda is massive enough that they’re gravity is strong enough that there is not enough space between them that the space was able to expand and push them apart against the force of gravity. So if you take the Milky Way, all of its stars and all of its gas and dust, all of its dark matter, you’re looking at something that’s a trillion times the mass of the sun. You have the same for Andromeda, and they’re less than a mega parsec apart – to Andromeda, its about 2.2 billion light years. And so with that distance and that much mass, that’s close enough that gravity is drawing them together. Most galaxies, because they’re so distant, you do see them moving away due to the expansion of the universe.”
“But actually M81, which is about 12 million light years away, is also moving towards the Milky Way. It’s the most distant galaxy that doesn’t show red shift. So there’s enough gravity in this local group – I guess the local group is typically the Milky Way galaxy, the Andromeda galaxy, the Triangulum galaxy, and however many tens of dwarf galaxies that we’ve either discovered or haven’t discovered yet. But there’s also a bubble of about ten to twenty major size galaxies extending out to about fifteen million light years or so, and that’s kind of right on the border between where the expansion of the universe would drive things apart and where the gravity is strong enough to hold things together.”
Since black holes are the most powerful gravitational spots in the entire Universe, can they distort light so much that it actually goes into orbit? And what would it look like if you could survive and follow light in this trip around a black hole?
I had this great question in from a viewer. Is it possible for light to orbit a black hole?
Consider this thought experiment, first explained by Newton. Imagine you had cannon that could shoot a cannonball far away. The ball would fly downrange and then crash into the dirt. If you shot the cannonball harder it would fly further before slamming into the ground. And if you could shoot the cannonball hard enough and ignore air resistance – it would travel all the way around the Earth. The cannonball would be in orbit. It’s falling towards the Earth, but the curvature of the Earth means that it’s constantly falling just over the horizon.
This works not only with cannonballs, astronauts and satellites, but with light too. This was one of the big discoveries that Einstein made about the nature of gravity. Gravity isn’t an attractive force between masses, it’s actually a distortion of spacetime. When light falls into the gravity well of a massive object, it bends to follow the curvature of spacetime.
Distant galaxies, the Sun, and even our own Earth will cause light to be deflected from its path by their distortion of spacetime. But it’s the incredible gravity of a black hole that can tie spacetime in knots. And yes, there is a region around a black hole where even photons are forced to travel in an orbit. In fact, this region is known as the “photon sphere”.
From far enough away, black holes act like any massive object. If you replaced the Sun with a black hole of the same mass, our Earth would continue to orbit in exactly the same way. But as you get closer and closer to the black hole, the orbiting object needs to go faster and faster as it whips around the massive object. The photon sphere is the final stable orbit you can have around a black hole. And only light, moving at, well, light speed, can actually exist at this altitude.
Artist impression of a black hole. Credit: ESO/L. Calçada
Imagine you could exist right at the photon sphere of a black hole. Which you can’t, so don’t try. You could point your flashlight in one direction, and see the light behind you, after it had fully orbited the black hole. You would also be bathed in the radiation of all the photons captured in this region. The visible light might be pretty, but the x-ray and gamma radiation would cook you like an oven.
Below the photon sphere you would see only darkness. Down there is the event horizon, light’s point of no return. And up above you’d see the Universe distorted by the massive gravity of the black hole. You’d see the entire sky in your view, even stars that would be normally obscured by the black hole, as they wrap around its gravity. It would be an awesome and deadly place to be, but it’d sure beat falling down below the event horizon.
If you could get down into the photon sphere, what kind of experiments would you want to do? Tell us in the comments below.
The movie ‘Gravity’ ended up being a force to reckon with at the 86th Academy Awards on Sunday, with the space thriller pulling in seven Oscars — including Best Director.
Starring Sandra Bullock and George Clooney, the movie followed the aftermath of an orbital disaster. Despite criticism from some about the movie’s accuracy, the film picked up 10 nominations and numerous good vibes from critics. (The movie has a 97% “Fresh” rating on Rotten Tomatoes). You can see congratulations from NASA astronauts Mike Massimino and Cady Coleman below the jump.
“Like any other human endeavor, a film is a transformative experience, and I want to thank Gravity because for many of us involved in this film, it was definitely a transformative experience,” said director Alfonso Cuarón in his acceptance speech last night (March 2).
“And it’s good because it took so long, if not, it would be a waste of time. It really sucks,” he joked, “because for a lot of people, the transformative experience was wisdom. For me, it was just the colour of my hair.”
Among the people Cuarón paid tribute to was Sandra Bullock, who was nominated for ‘Best Lead Actress’ but lost out to Cate Blanchett, who won for her performance in Blue Jasmine.
Sandra Bullock in a still from the movie ‘Gravity.’ Credit: Regency Enterprises/Warner Bros. Entertainment
“You’re Gravity,’ Cuarón said to Bullock from the stage. “You’re the soul, heart of the film. You’re a most amazing collaborator and one of the best people I’ve ever met.”
The movie attracted 7 wins of its 10 Oscar nominations, failing to earn ‘Best Picture’ (which went to 12 Years A Slave), ‘Achievement in Production Design’ (given to American Hustle). and ‘Best Lead Actress’ Its wins were:
Best director (Alfonso Cuarón);
Achievement in cinematography (Emmanuel Lubezki);
Achievement in film editing (Alfonso Cuarón and Mark Sanger);
Achievement in music written for motion pictures (Original score) (Steven Price);
Achievement in sound editing (Glenn Freemantle);
Achievement in sound mixing (Skip Lievsay, Niv Adiri, Christopher Benstead and Chris Munro);
Achivement in visual effects (Tim Webber, Chris Lawrence, Dave Shirk and Neil Corbould).
Shepherd moon Prometheus hovers just inside the reflective F ring
Lit by eerie, reflected light from Saturn’s F ring (and a casting a faint shadow through a haze of icy “mist”) Saturn’s moon Prometheus can be seen in the raw image above, captured by Cassini’s narrow-angle camera on Feb. 5 from a distance of 667,596 miles (1,074,392 km). It’s also receiving some light reflected off Saturn, which is off frame at the top (where the outermost edge of the A ring and the Keeler gap can be seen.)
As the potato-shaped Prometheus approaches the ring it yanks fine, icy material in towards itself, temporarily stretching the bright particles into long streamers and gaps and even kicking up bright clumps in the ring. It’s a visual demonstration of gravity at work! Watch an animation of this below, made from images acquired just before and after the one above:
Streamers and clumps created by the passing Prometheus on Feb. 5, 2014. (NASA/JPL/SSI. Animation by Jason Major.)
At its longest Prometheus is about 92 miles (148 km) across, but only 42 miles (68 km) in width. It circles Saturn in a wave-shaped, scalloping orbit once every 14.7 hours.
This artist’s impression shows the exotic double object that consists of a tiny, but very heavy neutron star that spins 25 times each second, orbited every two and a half hours by a white dwarf star. The neutron star is a pulsar named PSR J0348+0432 that is giving off radio waves that can be picked up on Earth by radio telescopes. Although this unusual pair is very interesting in its own right it is also a unique laboratory for testing the limits of physical theories. This system is radiating gravitational radiation, ripples in spacetime. Although these waves cannot be yet detected directly by astronomers on Earth they can be detected indirectly by measuring the change in the orbit of the system as it loses energy. As the pulsar is so small the relative sizes of the two objects are not drawn to scale.
When we think of gravity, we typically think of it as a force between masses. When you step on a scale, for example, the number on the scale represents the pull of the Earth’s gravity on your mass, giving you weight. It is easy to imagine the gravitational force of the Sun holding the planets in their orbits, or the gravitational pull of a black hole. Forces are easy to understand as pushes and pulls.
But we now understand that gravity as a force is only part of a more complex phenomenon described the theory of general relativity. While general relativity is an elegant theory, it’s a radical departure from the idea of gravity as a force. As Carl Sagan once said, “Extraordinary claims require extraordinary evidence,” and Einstein’s theory is a very extraordinary claim. But it turns out there are several extraordinary experiments that confirm the curvature of space and time.
The key to general relativity lies in the fact that everything in a gravitational field falls at the same rate. Stand on the Moon and drop a hammer and a feather, and they will hit the surface at the same time. The same is true for any object regardless of its mass or physical makeup, and this is known as the equivalence principle.
Since everything falls in the same way regardless of its mass, it means that without some external point of reference, a free-floating observer far from gravitational sources and a free-falling observer in the gravitational field of a massive body each have the same experience. For example, astronauts in the space station look as if they are floating without gravity. Actually, the gravitational pull of the Earth on the space station is nearly as strong as it is at the surface. The difference is that the space station (and everything in it) is falling. The space station is in orbit, which means it is literally falling around the Earth.
The International Space Station orbiting Earth. Credit: NASA
This equivalence between floating and falling is what Einstein used to develop his theory. In general relativity, gravity is not a force between masses. Instead gravity is an effect of the warping of space and time in the presence of mass. Without a force acting upon it, an object will move in a straight line. If you draw a line on a sheet of paper, and then twist or bend the paper, the line will no longer appear straight. In the same way, the straight path of an object is bent when space and time is bent. This explains why all objects fall at the same rate. The gravity warps spacetime in a particular way, so the straight paths of all objects are bent in the same way near the Earth.
So what kind of experiment could possibly prove that gravity is warped spacetime? One stems from the fact that light can be deflected by a nearby mass. It is often argued that since light has no mass, it shouldn’t be deflected by the gravitational force of a body. This isn’t quite correct. Since light has energy, and by special relativity mass and energy are equivalent, Newton’s gravitational theory predicts that light would be deflected slightly by a nearby mass. The difference is that general relativity predicts it will be deflected twice as much.
Description of Eddington’s experiment from the Illustrated London News (1919).
The effect was first observed by Arthur Eddington in 1919. Eddington traveled to the island of Principe off the coast of West Africa to photograph a total eclipse. He had taken photos of the same region of the sky sometime earlier. By comparing the eclipse photos and the earlier photos of the same sky, Eddington was able to show the apparent position of stars shifted when the Sun was near. The amount of deflection agreed with Einstein, and not Newton. Since then we’ve seen a similar effect where the light of distant quasars and galaxies are deflected by closer masses. It is often referred to as gravitational lensing, and it has been used to measure the masses of galaxies, and even see the effects of dark matter.
Another piece of evidence is known as the time-delay experiment. The mass of the Sun warps space near it, therefore light passing near the Sun is doesn’t travel in a perfectly straight line. Instead it travels along a slightly curved path that is a bit longer. This means light from a planet on the other side of the solar system from Earth reaches us a tiny bit later than we would otherwise expect. The first measurement of this time delay was in the late 1960s by Irwin Shapiro. Radio signals were bounced off Venus from Earth when the two planets were almost on opposite sides of the sun. The measured delay of the signals’ round trip was about 200 microseconds, just as predicted by general relativity. This effect is now known as the Shapiro time delay, and it means the average speed of light (as determined by the travel time) is slightly slower than the (always constant) instantaneous speed of light.
A third effect is gravitational waves. If stars warp space around them, then the motion of stars in a binary system should create ripples in spacetime, similar to the way swirling your finger in water can create ripples on the water’s surface. As the gravity waves radiate away from the stars, they take away some of the energy from the binary system. This means that the two stars gradually move closer together, an effect known as inspiralling. As the two stars inspiral, their orbital period gets shorter because their orbits are getting smaller.
Decay of pulsar period compared to prediction (dashed curve). Data from Hulse and Taylor, Plotted by the author.
For regular binary stars this effect is so small that we can’t observe it. However in 1974 two astronomers (Hulse and Taylor) discovered an interesting pulsar. Pulsars are rapidly rotating neutron stars that happen to radiate radio pulses in our direction. The pulse rate of pulsars are typically very, very regular. Hulse and Taylor noticed that this particular pulsar’s rate would speed up slightly then slow down slightly at a regular rate. They showed that this variation was due to the motion of the pulsar as it orbited a star. They were able to determine the orbital motion of the pulsar very precisely, calculating its orbital period to within a fraction of a second. As they observed their pulsar over the years, they noticed its orbital period was gradually getting shorter. The pulsar is inspiralling due to the radiation of gravity waves, just as predicted.
Illustration of Gravity Probe B. Credit: Gravity Probe B Team, Stanford, NASA
Finally there is an effect known as frame dragging. We have seen this effect near Earth itself. Because the Earth is rotating, it not only curves spacetime by its mass, it twists spacetime around it due to its rotation. This twisting of spacetime is known as frame dragging. The effect is not very big near the Earth, but it can be measured through the Lense-Thirring effect. Basically you put a spherical gyroscope in orbit, and see if its axis of rotation changes. If there is no frame dragging, then the orientation of the gyroscope shouldn’t change. If there is frame dragging, then the spiral twist of space and time will cause the gyroscope to precess, and its orientation will slowly change over time.
Gravity Probe B results. Credit: Gravity Probe B team, NASA.
We’ve actually done this experiment with a satellite known as Gravity Probe B, and you can see the results in the figure here. As you can see, they agree very well.
Each of these experiments show that gravity is not simply a force between masses. Gravity is instead an effect of space and time. Gravity is built into the very shape of the universe.
Think on that the next time you step onto a scale.
The Universe is always surprising us with how little we know about… the Universe. It’s continuously presenting us with stuff we never imagined, or even thought possible. The search for extrasolar planets is a great example.
Since we started, astronomers have turned up over a thousand of them. These planets can be gigantic worlds with many times the mass of Jupiter, all the way down to little tiny planets smaller than Mercury. Astronomers are also finding one type of world that feels both familiar and yet totally alien… the super earth.
In the strictest sense, a super earth is just a planet with more mass than Earth, but less than a larger planet like Uranus or Neptune. So, you could have super earths made of rock and metal, or even ice and gas. These planets could have oceans and atmospheres, or made of nothing but hydrogen and helium. The goal, of course, is to find a rocky super earth located in the habitable zone. This is the region where the planets are the right distance from the star for liquid water to be present.
The first discovery of a potentially habitable super earth was in the star system Gliese 581.
Here, astronomers found 2 planets orbiting within the habitable zone. Gliese 581 c has a mass of 5 times the Earth, and orbits on the overly warm side of the habitable zone and, Gliese 581 d is 7.7 times the mass of the Earth, and is on the cold side of the zone.
We’ve now found dozens of super earths. One recent discovery, Kepler 11-b, has only 4 times the mass of the our planet and just 1.5 times its size.
You’re probably wondering about the gravity. The exact gravity depends on the ratio of the planet’s size to its mass. If you could stand on the surface of a super earth, you’d probably feel a higher gravity. Considering these planets can have 5 or more times the mass of Earth. But less gravity than you’d expect.
An increase in size makes a big difference. For example, if you could stand on the surface of Kepler 11-b, which is about 1.5 times bigger but a whopping 4 times more massive, you’d feel only 1.4 times the pull of Earth’s gravity.
Artist’s impression of the trio of super earths. Image credit: ESO
Here’s the big question. Could a super earth support life?
Aquatic life would be no problem. Once you’re in the ocean, the effects of gravity are balanced out by the buoyancy of water. How well life could survive on land and in the air depends on the gravity of the world. With higher gravity, plants and animals wouldn’t be able to grow as tall. Animals would need thicker legs to support their weight. If the atmosphere was denser, likely because of the higher gravity, flying creatures could move more slowly with larger wingspans.
If intelligent life does develop on a heavy gravity world, it will have a much harder time getting into space. Reaching orbital velocity is already tremendously difficult from Earth. Just imagine how much more difficult it would be to launch rockets if everything was twice as heavy.
So, a big thank you to the astronomers showing us that there are all kinds of crazy worlds out there.
Albert Einstein during a lecture in Vienna in 1921.
Credit: National Library of Austria/F Schmutzer/Public Domain
One of the benefits of being an astrophysicist is your weekly email from someone who claims to have “proven Einstein wrong”. These either contain no mathematical equations and use phrases such as “it is obvious that..”, or they are page after page of complex equations with dozens of scientific terms used in non-traditional ways. They all get deleted pretty quickly, not because astrophysicists are too indoctrinated in established theories, but because none of them acknowledge how theories get replaced.
For example, in the late 1700s there was a theory of heat known as caloric. The basic idea of caloric was that it was a fluid that existed within materials. This fluid was self-repellant, meaning it would try to spread out as evenly as possible. We couldn’t observe this fluid directly, but the more caloric a material has the greater its temperature.
Ice-calorimeter from Antoine Lavoisier’s 1789 Elements of Chemistry. (Public Domain)
From this theory you get several predictions that actually work. Since you can’t create or destroy caloric, heat (energy) is conserved. If you put a cold object next to a hot object, the caloric in the hot object will spread out to the cold object until they reach the same temperature. When air expands, the caloric is spread out more thinly, thus the temperature drops. When air is compressed there is more caloric per volume, and the temperature rises.
We now know there is no “heat fluid” known as caloric. Heat is a property of the motion (kinetic energy) of atoms or molecules in a material. So in physics we’ve dropped the caloric model in terms of kinetic theory. You could say we now know that the caloric model is completely wrong.
Except it isn’t. At least no more wrong than it ever was.
The basic assumption of a “heat fluid” doesn’t match reality, but the model makes predictions that are correct. In fact the caloric model works as well today as it did in the late 1700s. We don’t use it anymore because we have newer models that work better. Kinetic theory makes all the predictions caloric does and more. Kinetic theory even explains how the thermal energy of a material can be approximated as a fluid.
This is a key aspect of scientific theories. If you want to replace a robust scientific theory with a new one, the new theory must be able to do more than the old one. When you replace the old theory you now understand the limits of that theory and how to move beyond it.
In some cases even when an old theory is supplanted we continue to use it. Such an example can be seen in Newton’s law of gravity. When Newton proposed his theory of universal gravity in the 1600s, he described gravity as a force of attraction between all masses. This allowed for the correct prediction of the motion of the planets, the discovery of Neptune, the basic relation between a star’s mass and its temperature, and on and on. Newtonian gravity was and is a robust scientific theory.
Then in the early 1900s Einstein proposed a different model known as general relativity. The basic premise of this theory is that gravity is due to the curvature of space and time by masses. Even though Einstein’s gravity model is radically different from Newton’s, the mathematics of the theory shows that Newton’s equations are approximate solutions to Einstein’s equations. Everything Newton’s gravity predicts, Einstein’s does as well. But Einstein also allows us to correctly model black holes, the big bang, the precession of Mercury’s orbit, time dilation, and more, all of which have been experimentally validated.
So Einstein trumps Newton. But Einstein’s theory is much more difficult to work with than Newton’s, so often we just use Newton’s equations to calculate things. For example, the motion of satellites, or exoplanets. If we don’t need the precision of Einstein’s theory, we simply use Newton to get an answer that is “good enough.” We may have proven Newton’s theory “wrong”, but the theory is still as useful and accurate as it ever was.
Unfortunately, many budding Einsteins don’t understand this.
Binary waves from black holes. Image Credit: K. Thorne (Caltech) , T. Carnahan (NASA GSFC)
To begin with, Einstein’s gravity will never be proven wrong by a theory. It will be proven wrong by experimental evidence showing that the predictions of general relativity don’t work. Einstein’s theory didn’t supplant Newton’s until we had experimental evidence that agreed with Einstein and didn’t agree with Newton. So unless you have experimental evidence that clearly contradicts general relativity, claims of “disproving Einstein” will fall on deaf ears.
The other way to trump Einstein would be to develop a theory that clearly shows how Einstein’s theory is an approximation of your new theory, or how the experimental tests general relativity has passed are also passed by your theory. Ideally, your new theory will also make new predictions that can be tested in a reasonable way. If you can do that, and can present your ideas clearly, you will be listened to. String theory and entropic gravity are examples of models that try to do just that.
But even if someone succeeds in creating a theory better than Einstein’s (and someone almost certainly will), Einstein’s theory will still be as valid as it ever was. Einstein won’t have been proven wrong, we’ll simply understand the limits of his theory.
Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He’s also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts.
In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip.
What is the ‘Big Rip?’
If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990’s, you have the supernova surveys that are looking deeper into space than we’ve ever looked before, and measuring distances accurately to greater distances than we’ve ever seen before. Something really surprising came out, and that was what we’ll now use “dark energy” now to explain, and that is that the acceleration is not actually slowing down – it’s not even stopped. It’s actually getting faster, and if you look at the most distant objects, they’re actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result.
One of the ideas of trying to explain it is to use the “cosmological constant,” which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn’t like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn’t supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size.
Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute – no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble’s data to come up with the idea of what we now call the Big Bang.
So, the expansion’s happening – wait, it’s getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart.
However, there’s a possibility that it doesn’t work like that. There’s actually a little bit of experimental evidence right now that, although it’s not well-established, that there’s a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won’t matter – that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms.
So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you’ll have a universe with nothing left. That’s the ‘Big Rip’ – if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart.
You can find more information from Dr. Thad Szabo at his YouTube channel.
