An October 2014 gravity map of the Earth's oceans using data from the European Space Agency's CryoSat mission and the CNES-NASA Jason-1 satellite. Findings include "continental connections" between South American and Africa, and evidence of seafloor spreading in the Gulf of Mexico that took place 150 million years ago. The red dots are volcanoes. Credit: Scripps Institution of Oceanography
Volcanoes! Seafloor spreading! Hidden ridges and mountains! These are the wonders being revealed in new maps of Earth’s sea floor. And no, it didn’t require a deep-sea dive to get there. Instead we got this information from a clever use of gravity (combining the data of two satellites making measurements from orbit.)
The data has caught the attention of Google, which plans to use this data for its upcoming ocean maps release. Scientists also say the information will tell us more about the 80% of the ocean floor that is either unexamined or obscured by thick sand.
So here’s where the data came from. The Scripps Institution of Oceanography combined information from two satellites — the European Space Agency’s ongoing CryoSat mission and the now defunct Jason-1 satellite from NASA and the French space agency CNES, which was decommissioned in 2013 after nearly 12 years of operations.
CryoSat is designed to map the thickness of ice using a radar altimeter (which is a clue to the effects of climate change). But this altimeter can be used all over the world, including to look at how high the sea floor is. Jason-1, for its part, was told to look at the Earth’s gravity field in the last year of its mission. And what a world pops out when this data is used.
A 2014 view of the Earth’s sea floor using data from the European Space Agency’s CryoSat mission and the CNES-NASA Jason-1 satellite. Credit: Scripps Institution of Oceanography
“The effect of the slight increase in gravity caused by the mass of rock in an undersea mountain is to attract a mound of water several meters high over the seamount. Deep ocean trenches have the reverse effect,” ESA wrote in a statement. “These features can only be detected by using radar altimetry from space.”
Some of the new findings include finding new bridges between Africa and South America and uncovering seafloor spreading that happened in the Gulf of Mexico 150 million years ago. Results based on the study, led by Scripps’ David Sandwell, recently appeared in the journal Science.
Long-time readers of Universe Today may also recall a gravity map from ESA’s Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), which revealed Earth’s gravity as a lumpy potato shape in 2011.
Is there any place in the Universe where there’s truly nothing? Consider the gaps between stars and galaxies? Or the gaps between atoms? What are the properties of nothing?
I want you to take a second and think about nothing. Close your eyes. Picture it in your mind. Focus. Fooooocus. On nothing….It’s pretty hard, isn’t it? Especially when I keep nattering at you.
Instead, let’s just consider the vast spaces between stars and galaxies, or the gaps between atoms and other microscopic particles. When we talk about nothing in the vast reaches between of space, it’s not actually, technically nothing. Got that? It’s not nothing. There’s… something there.
Even in the gulfs of intergalactic space, there are hundreds or thousands of particles in every cubic meter. But even if you could rent MegaMaid from a Dark Helmet surplus store, and vacuum up those particles, there would still be wavelengths of radiation, stretching across vast distances of space.
There’s the inevitable reach of gravity stretching across the entire Universe. There’s the weak magnetic field from a distant quasar. It’s infinitesimally weak, but it’s not nothing. It’s still something.
Philosophers, and some physicists, argue that *that* nothing isn’t the same as “real” nothing. Different physicists see different things as nothing, from nothing is classical vacuum, to the idea of nothing as undifferentiated potential.
Even if you could remove all the particles, shield against all electric and magnetic fields, your box would still contain gravity, because gravity can never be shielded or cancelled out. Gravity doesn’t go away, and it’s always attractive, so you can’t do anything to block it. In Newton’s physics that’s because it is a force, but in general relativity space and time *are* gravity.
Quantum theory includes strange particles like these quarks, seen here in a three-dimensional computer-generated simulation. PASIEKA/SPL
So, imagine if you could remove all particles, energy, gravity… everything from a system. You’d be left with a true vacuum. Even at its lowest energy level, there are fluctuations in the quantum vacuum of the Universe. There are quantum particles popping into and out of existence throughout the Universe. There’s nothing, then pop, something, and then the particles collide and you’re left with nothing again. And so, even if you could remove everything from the Universe, you’d still be left with these quantum fluctuations embedded in spacetime.
There are physicists like Lawrence Krauss that argue the “universe from nothing”, really meaning “the universe from a potentiality”. Which comes down to if you add all the mass and energy in the universe, all the gravitational curvature, everything… it looks like it all sums up to zero. So it is possible that the universe really did come from nothing. And if that’s the case, then “nothing” is everything we see around us, and “everything” is nothing.
What do you think? How do you wrap your head around the idea of nothing? Tell us in the comments below. And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Anyone who lives close to ocean is familiar with the tides. And you probably know they have something to do with the Moon. But how do the tides work? Do other planets experience tides?
Just what the heck are tides? Some kind of orbit jiggle jello effect from the magic Etruscan space-whale song? Is it an unending slap-back of gravitometric Malthusian resonance originating from the core of the Sun’s crystalline liver-light organelles? Is it all the plankton agreeing to paddle in the same direction at their monthly oceanic conferences?
As certain as I am that you enjoy my word terminology salads, with apologies to Papa Bear, we both know tides are caused by the gravitational interaction with the Moon. You would think we’d have only one high tide and one low tide, with the Moon pulling the Earth’s water towards it. Moon goes one side, water rushes over to that side, moon goes to other side, water chases around to follow it. But the tides make the water levels appear to rise twice a day, and lower twice a day in 6 hour increments. So, it’s clearly more complicated than that.
The gravity from the Moon does pull the water towards it. That’s what gives you the highest tide of the day. It’s a bulge of water that follows the Moon around and around as the Earth rotates. This makes sense to us. But then Earth itself is pulled with a little less gravity than the water towards the Moon and, the water on the opposite side of the Earth is pulled with even less gravity, and so you wind up with another bulge on the opposite side of the Earth.
So from our perspective, you end up with a bulge of water towards the Moon, and a bulge away from it. The part of the Earth with the water getting pulled towards the Moon experiences a high tide, and same with the part on the opposite side of the Earth with the other bulge. Correspondingly, the parts of the Earth at right angles are experiencing low tides.
It would be hard enough to predict with a simple spherical Earth covered entirely by water, but we’ve got continents and coastlines, and that makes things even more complicated. The levels that the tides rise and fall depend quite a bit on how easily the water can move around in a region. That’s why you can get such big tides in places like the Bay of Fundy in Canada.
The Moon over Gulf Islands National Seashore near Navarre Beach, Florida. Credit: Mindi Meeks.
Our Sun also contributes to the tides. Surprisingly, it accounts for about 30% of the them. So when the Sun and the Moon are lined up in the sky, you get the highest high tides and the lowest low tides – these are Spring Tides. And then when the Sun and Moon are at right angles, you get the lowest high tides and the highest low tides. These are Neap Tides.
Tidal forces can be very powerful. They can tear galaxies apart and cause moons to get shredded into pieces. Perhaps the most dramatic example is how Jupiter’s enormous gravity pulls on Io so strongly that its surface rises and falls by 100 meters. This is 5 times greater than the Earth’s biggest water tides. This constant rise and fall heats up the moon, giving it non-stop volcanism.
What do you think? Share your favorite tidal science fact in the comments below. And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
We’re total litterbugs. Here on Earth, and out in space. What are some strategies that have been developed to clean up all that junk in space and make it safer to explore?
Humans are great at lots of things. We’ve built amazing landmarks, great works of art, and have a legacy of unique cultures and languages spanning the globe…
We’re also great at not cleaning up after ourselves. As if the oceanic garbage patches weren’t enough, humans are actually filling space with junk too.
That’s okay, right? Space might be infinite, and if you average the amount of stuff we know about versus the amount of space, there’s barely anything out there at all. Space can handle all that junk, right? Right? Sure it can! Space is just fine. Don’t you worry for one second about space. Space is big. Sure it’d kill us in a heartbeat, but it’s got no feelings to hurt! It’s just space!
Now I’m going to encourage you to be a little selfish, as this actually a problem for us. I know, it’s hard to believe that somehow, with our baked-in levels of neglect, we’re creating a global problem for us and future generations. I feel like this our thing now. It’s what defines us. Our littering up of space might prevent humans from ever being able to escape our planet again.
Here’s the deal. In the decades that humans have been launching stuff into space, nobody ever thought too hard about what we should do about our rockets and satellites after we’re done with them. It’s not like you can ever fill up space.
Astronomers are currently tracking 19,000 individual objects larger than 5 cm, and there are likely more than 300,000 objects smaller than 1 cm. All this stuff sticks around and continues to orbit the Earth. Over time debris collides with more debris, creating smaller and smaller pieces of space junk.
Some scientists are concerned that we might reach a point where this junk forms an impenetrable shield of shrieking metal around the Earth, that would tear apart any spacecraft that tries to leave our planet. I like to call this the “Spacelitter Singularity”. It’s an unstoppable cascade of collisions and chaos that converts the area around the Earth into a relentless blender of progressively smaller and smaller high velocity projectiles. Which would be bad.
Image plot of space junk. Image credit: NASA
So, how do we avoid that? How can we minimize the amount of space junk we throw into orbit? And how can get rid of the garbage that’s already out there? For starters, anyone launching stuff into space needs to minimize the amount of debris they generate. Rockets should maneuver back into the atmosphere to burn up. Astronauts need to keep track of their tools and gloves.
Engineers would also need to plan out what will happen to their spacecraft at the end of their lives. Instead of letting them just die, mission controllers need to be able to maneuver spacecraft into a safer parking orbit, or alternately, back into the atmosphere.
Something will need to be done with the space junk that’s already out there, chopping itself into smaller and smaller pieces. One idea is to have a one-up, one-down policy rule for companies. For every spacecraft they launch, they collect and de-orbit another spacecraft in roughly the same orbit. Or we could create a special junk removal spacecraft.
Space Junk. Image credit: Jonas Bendiksen/Eurasianet.org
These would use efficient ion engines to track and dock with pieces of space junk, collecting them together. Once the spacecraft had collected enough material, or run out of fuel, it could be safely de-orbited, or possibly transform into garbage truck Voltron.
The most awesome idea I’ve come across is to build a space-based laser system that could target and fire on pieces of space debris as they go by. Small pieces would be vaporized, and larger objects would be slowed down as the vaporization would act as a decelerating thrust, lowering their orbit. That’s right, one solution is to build a real life game of Asteroids.
Once again, a lack of forethought has a created a problem that will trouble future generations. Getting into space in the first place is super hard, and cleaning it up is going to take more work than we ever thought.
What do you think? How should we clean up space to make it safe for future generations of space faring humans? Tell us in the comments below.
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Have you ever heard that spacecraft can speed themselves up by performing gravitational slingshot maneuvers? What’s involved to get yourself going faster across the Solar System.
Let’s say you want to go back in time and prevent Kirk from dying on the Enterprise B.
You could use a slingshot maneuver. You’d want to be careful that you don’t accidentally create an alternate reality future where the Earth has been assimilated by the Borg, because Kirk wasn’t in the Nexus to meet up with Professor Picard and Sir Iandalf Magnetopants, while they having the best time ever gallivanting around New York City.
*sigh* Ah, man. I really love those guys. What was I saying? Oh right. One of the best ways to increase the speed of a spacecraft is with a gravitational slingshot, also known as a gravity assist.
There are times that fantasy has bled out too far into the hive mind, and people confuse a made up thing with an actual thing because of quirky similarities, nomenclature and possibly just a lack of understanding.
So, before we go any further a “gravitational slingshot” is a gravity assist that will speed up an actual spacecraft, “slingshot maneuver” is made up bananas nonsense. For example, when Voyager was sent out into the Solar System, it used gravitational slingshots past Jupiter and Saturn to increase its velocity enough to escape the Sun’s gravity.
So how do gravitational assists work? You probably know this involves flying your spacecraft dangerously close to a massive planet. But how does this help speed you up? Sure, as the spacecraft flies towards the planet, it speeds up. But then, as it flies away, it slows down again. Sort of like a skateboarder in a half pipe.
This process nets out to zero, with no overall increase in velocity as your spacecraft falls into and out of the gravity well. So how do they do it? Here’s the trick. Each planet has an orbital speed travelling around the Sun.
As the spacecraft approaches the planet, its gravity pulls the much lighter spacecraft so that it catches up with the planet in orbit. It’s the orbital momentum from the planet which gives the spacecraft a tremendous speed boost. The closer it can fly, the more momentum it receives, and the faster it flies away from the encounter.
To kick the velocity even higher, the spacecraft can fire its rockets during the closest approach, and the high speed encounter will multiply the effect of the rockets. This speed boost comes with a cost. It’s still a transfer of momentum. The planet loses a tiny bit of orbital velocity.
If you did enough gravitational slingshots, such as several zillion zillion slingshots, you’d eventually cause the planet to crash into the Sun. You can use gravitational slingshots to decelerate by doing the whole thing backwards. You approach the planet in the opposite direction that it’s orbiting the Sun. The transfer of momentum will slow down the spacecraft a significant amount, and speed up the planet an infinitesimal amount.
Messenger’s complicated flyby trajectory. Credit: NASA
NASA’s MESSENGER spacecraft made 2 Earth flybys, 2 Venus flybys and 3 Mercury flybys before it was going slowly enough to make an orbital insertion around Mercury. Ulysses, the solar probe launched in 1990, used gravity assists to totally change its trajectory into a polar orbit above and below the Sun. And Cassini used flybys of Venus, Earth and Jupiter to reach Saturn with an efficient flight path.
Nature sure is trying to make it easy for us. Gravitational slingshots are an elegant way to slow down spacecraft, tweak their orbits into directions you could never reach any other way, or accelerate to incredible speeds.
It’s a brilliant dance using orbital mechanics to aid in our exploration of the cosmos. It’s a shining example of the genius and the ingenuity of the minds who are helping to push humanity further out into the stars.
What do you think? What other places is the general comprehension between actual facts and fictional knowledge blurring, just like the “slingshot maneuver” and “gravitational slingshot”?
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Have you ever heard that people go crazy during a full Moon? What’s going on to cause all this lunacy? Or maybe, just maybe, it’s all a myth and nothing special ever happens during full moons.
If I went crazy, like real actual cluster-cuss crazy, you might call me a lunatic. Or you might say I suffered from lunacy. What does that even mean? This word comes from lunaticus, meaning “of the moon” or moonstruck. It was more popular during the late 1800’s, yet it still hangs around.
Surely it must still be an important and useful diagnostic medical term. As when the Moon is full, everyone goes crazy. It’s called the lunar effect. Everyone knows that. Right?
People have theorized for thousands of years that the Moon has all kinds of impacts on us. It affects fertility, crime rates, dog attacks, and increases blood loss during surgery. It must be a full Moon, they say. Full moon tomorrow night! All the crazies will be out! they say.
So what causes all this moon madness. What makes us sprout metaphorical canines and race around in a fugue state hungry for manflesh when the moon is full? Are we experiencing tidal forces from the Moon on our internal organ juices? Is it a result of us evolving lockstep with the lunar cycle? Perhaps the light coming from the Moon affects our visual cortex in a way to stimulate the animalistic parts of the brain? It has been with us for so long as a belief, there must be something to it. Right?
Nope, it’s all a myth. All of it. Tidal effects on behaviour aren’t happening. We experience two high and two low tides every day, and it has nothing to do with the phase of the Moon. In fact, your body experiences more gravity from your chair than it does from the Moon. If the motion of blood was somehow that reactive, should you step into a full elevator everyone would pass out with all the blood rushing to their extremities pulled by your gravity.
No way! You say! It’s true! Because the Moon is closer when it’s full, and its tug on our “materia” and “humors” is stronger. Unfortunately for this theory, our Moon travels an elliptical orbit, and the time when the Moon is closest has nothing to do with when it’s full.
The Moon can be full and close – supermoon. Or it can be full but farther away – minimoon.
Full Moon Rising Over Northwest Georgia on June 22nd, 2013. Credit and copyright: Stephen Rahn.
In 1985, a team of scientists did a meta study, looking at 37 separate research papers that attempted to study the Moon’s impact on all aspects of humanity. They found papers that demonstrated a correlation, and then promptly found the mistakes in the research. They found absolutely no evidence. We don’t get into more car accidents. Hospital rooms aren’t more crowded. Werewolves aren’t apparently a thing.
We do notice the coincidences, when something strange occurs and there happens to be a full Moon. But we don’t notice all the times when there wasn’t a full Moon. To learn more about this, I’d suggest heading over to the wonderful blog “You are not so smart” by David McRaney, and reading up on “Confirmation Bias”.
So, where did this idea come from? Historians suspect it’s possible that the brightness of a full moon disturbed people’s sleep schedules.
I’m partial to the idea that in history, the full Moon was a high time for people to be active at night, favoring work or travel by the light of the full moon. So, perhaps there were more accidents.
But not any more. People are superstitious about mundane things like black cats, ladders and broken mirrors, it’s not surprising they’re superstitious about our beautiful and bright companion prettying up the sky almost every night.
What do you think? What’s your favorite full moon superstition? Tell us in the comments below.
Goodbye Moon. Every year, the Moon slips a few centimeters away from us, slowing down our day. Why is the Moon drifting away from us, and how long will it take before the Earth and the Moon are tidally locked to each other?
We had a good run, us and the Moon. Grab your special edition NASA space tissues because today we’re embarking on a tale of orbital companionship, childhood sweethearts and heartache.
You could say we came from the same part of town. A long time ago the Mars-sized object Theia, collided with the Earth and the Moon was formed out of the debris from the collision.
We grew up together. Counting from the very beginning, this relationship has lasted for 4.5 billion years. We had some good times. Some bad times. Gravitationally linked, arm in arm, inside our solar family sedan traversing the galaxy.
But now, tragedy. The Moon, OUR Moon, is moving on to brighter horizons. We used to be much closer when we were younger and time seemed to fly by much faster. In fact, 620 million years ago, a day was only 21 hours long. Now they’ve dragged out to 24 hours and they’re just getting longer, and the Moon is already at a average distance of 384,400 km. It almost feels too far away.
If we think back far enough to when we were kids, there was a time when a day was just 2 – 3 hours long, and the Moon was much closer. It seemed like we did everything together back then. But just like people, massive hunks of rock and materials flying through space change, and their relationships change as well.
Our therapist told us it wasn’t a good idea to get caught up on minutiae, but we’ve done some sciencing using the retroreflector experiments placed by Apollo astronauts, and it looks as though the Moon has always had one foot out the door.
Today it’s drifting away at 1-2 cm/year. Such heartache! We just thought it seemed like the days were longer, but it’s not just an emotional effect of seeing our longtime friend leaving us, there’s a real physical change happening. Our days are getting 1/500th of a second longer every century.
I can’t help but blame myself. If only we knew why. Did the Moon find someone new? Someone more attractive? Was it that trollop Venus, the hottest planet in the whole solar system? It’s really just a natural progression. It’s nature. It’s gravity and tidal forces.
And no, that’s not a metaphor. The Earth and the Moon pull at each other with their gravity. Their shapes get distorted and the pull of this tidal force creates a bulge. The Earth has a bulge facing towards the Moon, and the Moon has a more significant bulge towards the Earth.
A series of photos combined to show the rise of the July 22, 2013 ‘super’ full moon over the Rocky Mountains, shot near Vail, Colorado, at 10,000ft above sea level in the White River National Forest. Moon images are approximately 200 seconds apart. Credit and copyright: Cory Schmitz
These bulges act like handles for gravity, which slows down their rotation. The process allowed the Earth’s gravity to slow the Moon to a stop billions of years ago. The Moon is still working on the Earth to change its ways, but it’ll be a long time before we become tidally locked to the Moon.
This slowing rotation means energy is lost by the Earth. This energy is transferred to the Moon which is speeding up, and as we’ve talked about in previous episodes the faster something orbits, the further and further it’s becomes from the object it’s orbiting.
Will it ever end? We’re so attached, it seems like it’ll take forever to figure out who’s stuff belongs to who and who gets the dog. Fear not, there is an end in sight. 50 billion years from now, 45 billion years after the Sun has grown weary of our shenanigans and become a red giant, when the days have slowed to be 45 hours long, the Moon will consider itself all moved into its brand new apartment ready to start its new life.
What about the neighbors down the street? How are the other orbital relationships faring. I know there’s a lot of poly-moon-amory taking place out there in the Solar System. We’re not the only ones with Moons tidally locked. There’s Phobos and Deimos to Mars, many of the moons of Jupiter and Saturn are, and Pluto and Charon are even tidally locked to each other, forever. Now’s that’s real commitment. So, in the end. The lesson here is people and planets change. The Moon just needs its space, but it still wants to be friends.
What do you think? If you were writing a space opera about the Earth and the Moon break-up, what was it that finally came between them? Tell us in the comments below.
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.”
