Einstein was right
May 4, 2011 11:39 AM Subscribe
"There is a space-time vortex around Earth, and its shape precisely matches the predictions of Einstein's theory of gravity." NASA announces result of elaborate experiment to prove Einstein's inferences about space time. The engineering involved in this blows me away. More links within the article...
Uh, so how did they measure the gyros without touching them?
posted by GuyZero at 11:45 AM on May 4, 2011
posted by GuyZero at 11:45 AM on May 4, 2011
I'll measure your gyro without touching it.
posted by ZaneJ. at 11:47 AM on May 4, 2011 [9 favorites]
posted by ZaneJ. at 11:47 AM on May 4, 2011 [9 favorites]
The four gyroscopes in GP-B are the most perfect spheres ever made by humans. These ping pong-sized balls of fused quartz and silicon are 1.5 inches across and never vary from a perfect sphere by more than 40 atomic layers.
Color me impressed.
posted by Lutoslawski at 11:48 AM on May 4, 2011 [5 favorites]
Color me impressed.
posted by Lutoslawski at 11:48 AM on May 4, 2011 [5 favorites]
Wibbly-wobbly timey-wimey
posted by KingEdRa at 11:49 AM on May 4, 2011 [12 favorites]
posted by KingEdRa at 11:49 AM on May 4, 2011 [12 favorites]
These ping pong-sized balls of fused quartz and silicon
And they are un-hittable when I get a little top spin on them.
posted by GuyZero at 11:49 AM on May 4, 2011 [2 favorites]
And they are un-hittable when I get a little top spin on them.
posted by GuyZero at 11:49 AM on May 4, 2011 [2 favorites]
epic, epic, epic, researchers chanted. experts announced epic findings that were discovered to be epic.
posted by TwelveTwo at 11:49 AM on May 4, 2011
posted by TwelveTwo at 11:49 AM on May 4, 2011
Where can I get one of those gyroscopes? I've got a marble run to build.
posted by borkencode at 11:50 AM on May 4, 2011
posted by borkencode at 11:50 AM on May 4, 2011
NASA has balls. Perfect balls.
posted by Hairy Lobster at 11:50 AM on May 4, 2011 [24 favorites]
posted by Hairy Lobster at 11:50 AM on May 4, 2011 [24 favorites]
Explanation of gyro measurement here.
The answer comes through the phenomenon of superconductivity. Superconductivity provides a spin pointer which is neither optical nor mechanical as in conventional gyroscopes but magnetic. It also provides a sensitive non-interfering instrument to read the pointer, the Superconducting Quantum Interference Device (SQUID).
posted by empath at 11:51 AM on May 4, 2011
The answer comes through the phenomenon of superconductivity. Superconductivity provides a spin pointer which is neither optical nor mechanical as in conventional gyroscopes but magnetic. It also provides a sensitive non-interfering instrument to read the pointer, the Superconducting Quantum Interference Device (SQUID).
posted by empath at 11:51 AM on May 4, 2011
What's really interesting to me is that a spinning mass will deform the space around it. Wow.
posted by Xoebe at 11:51 AM on May 4, 2011
posted by Xoebe at 11:51 AM on May 4, 2011
the Superconducting Quantum Interference Device (SQUID).
I love physics acronyms.
posted by kmz at 11:53 AM on May 4, 2011 [5 favorites]
I love physics acronyms.
posted by kmz at 11:53 AM on May 4, 2011 [5 favorites]
I don't get it. So... there's this what around earth that does what, that Einstein somehow theorized it was there and it means what for whom?
(admittedly, whenever anyone mentions space/time anything, I think of Star Trek, but I am honestly confused here)
posted by Debaser626 at 11:56 AM on May 4, 2011
(admittedly, whenever anyone mentions space/time anything, I think of Star Trek, but I am honestly confused here)
posted by Debaser626 at 11:56 AM on May 4, 2011
Wow. I don't yet understand every single element, but wow.
posted by cashman at 11:59 AM on May 4, 2011
posted by cashman at 11:59 AM on May 4, 2011
There is a space-time vortex around Earth is going to be the next TimeCube.
posted by casarkos at 12:00 PM on May 4, 2011 [1 favorite]
posted by casarkos at 12:00 PM on May 4, 2011 [1 favorite]
Just as an amusing note with regard to the post's title, Dr. Will published a book named Was Einstein Right? some years back, all about the experimental tests going on then and the competing hypotheses.
posted by adipocere at 12:00 PM on May 4, 2011
posted by adipocere at 12:00 PM on May 4, 2011
Uh, so how did they measure the gyros without touching them?
They were coated with a *very* thin layer of Niobium, then chilled to 2K, which made the Niobium superconductive. Detecting the rotation of the gyros in this state is trival, use a SQUID.
The issue that this experiment ran into was noise -- there was a lot more torque in the gyros than they expected, the spheres developed an electrostatic axis (different from the rotational axis) which caused a torque effect, and dissipation of the magnetic field was much worse than expected, also causing torque. Given that the measurement that they were trying to make was the effect of the gravitational field and frame dragging, which they would see as torque on the gyro, this was a huge issue. After the initial data release, most thought we'd not get any useful data at all from this experiment -- both effects had torque forces similar to what the actual signal would be.
But the GP-B team pulled a clever. After the science phase, they deliberately misaligned the spacecraft and took data for a couple of days. This caused the torque caused by gravitational and frame dragging effects to shift axis, but the local sources in the spacecraft stayed the same. Then, they had to painstakingly analyze the difference, and then subtract the difference from the science data, leaving only the signal they were searching for.
This is a really amazing effort saving an experiment that would otherwise have failed. No result isn't a failure (maybe the effect doesn't exist!) but this would have been, in that with the extra noise, the signal would have been unreadable, so it could niether confirm nor deny the effect it was looking for.
I'm glad they were able to figure out the local torque effects and extract the gravitational ones -- and the numbers are spot on to General Relativity. They were out to confirm GR, and they found number that confirm.
Of course, now other people are going to take a very hard stare at thier data reduction to make sure they didn't introduce a bias.
posted by eriko at 12:00 PM on May 4, 2011 [47 favorites]
They were coated with a *very* thin layer of Niobium, then chilled to 2K, which made the Niobium superconductive. Detecting the rotation of the gyros in this state is trival, use a SQUID.
The issue that this experiment ran into was noise -- there was a lot more torque in the gyros than they expected, the spheres developed an electrostatic axis (different from the rotational axis) which caused a torque effect, and dissipation of the magnetic field was much worse than expected, also causing torque. Given that the measurement that they were trying to make was the effect of the gravitational field and frame dragging, which they would see as torque on the gyro, this was a huge issue. After the initial data release, most thought we'd not get any useful data at all from this experiment -- both effects had torque forces similar to what the actual signal would be.
But the GP-B team pulled a clever. After the science phase, they deliberately misaligned the spacecraft and took data for a couple of days. This caused the torque caused by gravitational and frame dragging effects to shift axis, but the local sources in the spacecraft stayed the same. Then, they had to painstakingly analyze the difference, and then subtract the difference from the science data, leaving only the signal they were searching for.
This is a really amazing effort saving an experiment that would otherwise have failed. No result isn't a failure (maybe the effect doesn't exist!) but this would have been, in that with the extra noise, the signal would have been unreadable, so it could niether confirm nor deny the effect it was looking for.
I'm glad they were able to figure out the local torque effects and extract the gravitational ones -- and the numbers are spot on to General Relativity. They were out to confirm GR, and they found number that confirm.
Of course, now other people are going to take a very hard stare at thier data reduction to make sure they didn't introduce a bias.
posted by eriko at 12:00 PM on May 4, 2011 [47 favorites]
There is a space-time vortex around Earth
Didn't the tenth Doctor use it as a tow-rope to haul the Earth back into its spot using the TARDIS?
posted by George_Spiggott at 12:03 PM on May 4, 2011 [1 favorite]
Didn't the tenth Doctor use it as a tow-rope to haul the Earth back into its spot using the TARDIS?
posted by George_Spiggott at 12:03 PM on May 4, 2011 [1 favorite]
This is why we need to keep funding basic R&D. The average person looks at this article and thinks, Who Cares? But it's more than just the science, which is amazing in and of itself. It's all the secondary technologies that are developed to get at the science! Just from this one experiment we get drag reduction technologies, magnetic shielding, and supergyros. Add those to your tech tree and smoke it.
posted by backseatpilot at 12:03 PM on May 4, 2011 [19 favorites]
posted by backseatpilot at 12:03 PM on May 4, 2011 [19 favorites]
Oh, numbers: Predicted by theory, frame drag should be 0.041 arc seconds a year. Measured: 0.039+- 0.007 arcsec/year. Geodetic Precession was predicted at 6.601 arcsec/year, and measured 6.600 +- 0.017arcsec/year.
Sweet fit.
posted by eriko at 12:05 PM on May 4, 2011 [10 favorites]
Sweet fit.
posted by eriko at 12:05 PM on May 4, 2011 [10 favorites]
Another interesting bit is that that experiment was launched 47 years ago. That is a long damn time to be running one experiment.
Hard to believe they could make stuff with such amazing precision in 1963.
posted by Malor at 12:12 PM on May 4, 2011
Hard to believe they could make stuff with such amazing precision in 1963.
posted by Malor at 12:12 PM on May 4, 2011
eriko, you made that make sense.
I bow before your powers of description.
posted by From Bklyn at 12:12 PM on May 4, 2011 [5 favorites]
I bow before your powers of description.
posted by From Bklyn at 12:12 PM on May 4, 2011 [5 favorites]
+1, well said sir.
posted by RolandOfEld at 12:19 PM on May 4, 2011
posted by RolandOfEld at 12:19 PM on May 4, 2011
Another interesting bit is that that experiment was launched 47 years ago
funding and research started that long ago, it wasn't launched until recently.
posted by empath at 12:22 PM on May 4, 2011
funding and research started that long ago, it wasn't launched until recently.
posted by empath at 12:22 PM on May 4, 2011
Here's a bit more about the Polhode motion they had to correct for. I don't know what is more incredible, that they had to model such an effect in the first place, or that they the instrument was generating data with such a level of sensitivity that they could come up with an accurate enough model to fully explain the deviations they were seeing.
posted by the painkiller at 12:22 PM on May 4, 2011
posted by the painkiller at 12:22 PM on May 4, 2011
the Superconducting Quantum Interference Device (SQUID)
A triumphant NASA spokesperson was quoted as saying: "I can get you what you want. You just have to talk to me. I'm your priest, your shrink, your main connection to the switchboard of souls. I'm the Magic Man, the Santa Claus of the Subconscious. You say it, you even think it, you can have it. You want a girl, you want two girls? I don't know what your thing is or what you're curious about... you want a guy? You want to be a girl... see what that feels like? You want a nun to tie you up? It's all do-able."
posted by Durn Bronzefist at 12:22 PM on May 4, 2011 [5 favorites]
A triumphant NASA spokesperson was quoted as saying: "I can get you what you want. You just have to talk to me. I'm your priest, your shrink, your main connection to the switchboard of souls. I'm the Magic Man, the Santa Claus of the Subconscious. You say it, you even think it, you can have it. You want a girl, you want two girls? I don't know what your thing is or what you're curious about... you want a guy? You want to be a girl... see what that feels like? You want a nun to tie you up? It's all do-able."
posted by Durn Bronzefist at 12:22 PM on May 4, 2011 [5 favorites]
Also: fucking outstanding.
posted by Durn Bronzefist at 12:29 PM on May 4, 2011
posted by Durn Bronzefist at 12:29 PM on May 4, 2011
NASA funding for Gravity Probe B began in the fall of 1963. That means Everitt and some colleagues have been planning, promoting, building, operating, and analyzing data from the experiment for more than 47 years—truly, an epic effort.
crikey
posted by memebake at 12:30 PM on May 4, 2011 [1 favorite]
crikey
posted by memebake at 12:30 PM on May 4, 2011 [1 favorite]
Hard to believe they could make stuff with such amazing precision in 1963.
Quartz without tooling marks? Meh, been done.
posted by rough ashlar at 12:47 PM on May 4, 2011
Quartz without tooling marks? Meh, been done.
posted by rough ashlar at 12:47 PM on May 4, 2011
I'm glad they were able to figure out the local torque effects and extract the gravitational ones -- and the numbers are spot on to General Relativity. They were out to confirm GR, and they found number that confirm.
this is strange framing,. this experiment is exactly the situation: low gravity medium distance where it would be really surprising if there were significant devations from gr. so surprising that they would have to be explainable by obscure effects. i'm not sure why they did this experiment at all... except that experimental physicists are an awful conservative bunch.
I think the point of this is that if you want to do geodesy to general relativistic precision you need to account for lag due to the finite propagation speed of gravitational '"force" i.e. frame dragging. this is just a super accurate measurement of that lag.
posted by ennui.bz at 12:52 PM on May 4, 2011
this is strange framing,. this experiment is exactly the situation: low gravity medium distance where it would be really surprising if there were significant devations from gr. so surprising that they would have to be explainable by obscure effects. i'm not sure why they did this experiment at all... except that experimental physicists are an awful conservative bunch.
I think the point of this is that if you want to do geodesy to general relativistic precision you need to account for lag due to the finite propagation speed of gravitational '"force" i.e. frame dragging. this is just a super accurate measurement of that lag.
posted by ennui.bz at 12:52 PM on May 4, 2011
As mentioned upthread, this project has been going on since 1964. Last I heard, there were more than 100 PhD's awarded for work on this project, and by their own estimate, they spent $750 mil over 47 years. Further, since science has advanced significantly in the 47 years since its inception, the scientific impact of it's results have waned significantly as other, much cheaper projects have effectively scooped them (see here for an example).
On the one hand, I'm excited that they are getting good press as any positive science story is a good one in my book, but on the other hand this really is more of a marketing victory than a scientific one. One way that this is evident is the way they market the work: Einstein is everywhere. I would propose a law that the more one mentions Einstein in relation to one's work, the less likely it is to be significant.
posted by artichoke_enthusiast at 12:53 PM on May 4, 2011 [1 favorite]
On the one hand, I'm excited that they are getting good press as any positive science story is a good one in my book, but on the other hand this really is more of a marketing victory than a scientific one. One way that this is evident is the way they market the work: Einstein is everywhere. I would propose a law that the more one mentions Einstein in relation to one's work, the less likely it is to be significant.
posted by artichoke_enthusiast at 12:53 PM on May 4, 2011 [1 favorite]
Hairy Lobster: NASA has balls. Perfect ice cold superconducting niobium coated shiny balls.
FTFM
posted by Hairy Lobster at 1:01 PM on May 4, 2011 [5 favorites]
FTFM
posted by Hairy Lobster at 1:01 PM on May 4, 2011 [5 favorites]
What the article said about the gyroscope wobbling wildly in the event horizon of a black hole brings me back to the image I have of the universe in light of the ontology that general relativity proposes, which consists of all of us in three dimensions being guided along rails we can't see, and whose fidelity I can't vouch for. It's just so cool to me that there is a higher-dimensional shape to things embedded in our three spatial dimensions that causes shit like this to happen.
posted by invitapriore at 1:26 PM on May 4, 2011
posted by invitapriore at 1:26 PM on May 4, 2011
Well, we already knew that you need Niobium balls to trap a quark.
posted by COBRA! at 1:29 PM on May 4, 2011
posted by COBRA! at 1:29 PM on May 4, 2011
Totally acceptable use of "epic." This kind of thing makes me proud to be human.
posted by polyhedron at 1:41 PM on May 4, 2011 [1 favorite]
posted by polyhedron at 1:41 PM on May 4, 2011 [1 favorite]
the ontology that general relativity proposes, which consists of all of us in three dimensions being guided along rails we can't see
More that we exist as a 4 dimensional life-line. There's nothing that really privileges one moment in your life over any other.
posted by empath at 1:54 PM on May 4, 2011
More that we exist as a 4 dimensional life-line. There's nothing that really privileges one moment in your life over any other.
posted by empath at 1:54 PM on May 4, 2011
this experiment is exactly the situation: low gravity medium distance where it would be really surprising if there were significant devations from gr. so surprising that they would have to be explainable by obscure effects. i'm not sure why they did this experiment at all... except that experimental physicists are an awful conservative bunch.
So, because most of a theory is tested and accepted, we shouldn't bother testing other aspects and consequences of the theory? If you think frame-dragging isn't interesting enough to warrant testing, I can only imagine what must you think of the Eötvös experiment.
posted by chrismear at 2:35 PM on May 4, 2011
More that we exist as a 4 dimensional life-line. There's nothing that really privileges one moment in your life over any other.
Yeah, that's definitely the big picture image. The part that really gets me, though, is how the shape of space-time influences movement in the "space" dimensions. I guess gravity is the most obvious example of that, but things like gravitational lensing and the gyroscope in the black hole point out some of the less intuitive consequences of that fact.
posted by invitapriore at 2:56 PM on May 4, 2011
Yeah, that's definitely the big picture image. The part that really gets me, though, is how the shape of space-time influences movement in the "space" dimensions. I guess gravity is the most obvious example of that, but things like gravitational lensing and the gyroscope in the black hole point out some of the less intuitive consequences of that fact.
posted by invitapriore at 2:56 PM on May 4, 2011
More that we exist as a 4 dimensional life-line. There's nothing that really privileges one moment in your life over any other.The fraction of my wave-function which decided to read Metafilter this afternoon laughs at your puny 4 dimensions. Oh, if only the portions of me from which these time-lines decohered could have read that, most of them would have been quite amused...
posted by roystgnr at 3:07 PM on May 4, 2011 [1 favorite]
That's it Science. I've had it with you.
I've read the linked article, and on some simple level, I understand that this is tremendously cool. But that's about as much as I can understand. So while I get that this is Important and Cool, I don't understand exactly how Important and Cool this is, so I'm moving to Plan B.
Plan B, for the record, is renounce science, accept that God created the Universe, and from that simple statement, everything else makes sense.
Hey God! Nice work on that space time vortex around Earth! To make it cooler, could it start and end in Cardiff, please?
posted by Effigy2000 at 3:08 PM on May 4, 2011 [1 favorite]
I've read the linked article, and on some simple level, I understand that this is tremendously cool. But that's about as much as I can understand. So while I get that this is Important and Cool, I don't understand exactly how Important and Cool this is, so I'm moving to Plan B.
Plan B, for the record, is renounce science, accept that God created the Universe, and from that simple statement, everything else makes sense.
Hey God! Nice work on that space time vortex around Earth! To make it cooler, could it start and end in Cardiff, please?
posted by Effigy2000 at 3:08 PM on May 4, 2011 [1 favorite]
Amazing. Also, the super spherical gyroscope balls look like they will be useful in Phantasm V.
posted by quarterframer at 3:09 PM on May 4, 2011
posted by quarterframer at 3:09 PM on May 4, 2011
the old physics joke
I thought it went "Assuming a perfectly spherical cow..."
posted by CheeseDigestsAll at 3:09 PM on May 4, 2011
I thought it went "Assuming a perfectly spherical cow..."
posted by CheeseDigestsAll at 3:09 PM on May 4, 2011
i'm not sure why they did this experiment at all
Because there had never been direct confirmation of geodetic precession or frame dragging in GR before -- there were measurements that had such large errors that they really couldn't confirm the theory. Some of them seemed more likely to disprove than prove, but once again, the errors were huge -- the signal they were looking for by theory is incredibly small. Kip Thorne described it thus: "In the realm of black holes and the universe, the language of general relativity is spoken, and it is spoken loudly. But in our tiny solar system, the effects of general relativity are but whispers."
GP-B has basically nailed down geodetic precession, and has come pretty close to nailing down frame dragging. Really, the only prediction of GR that doesn't have direct experimental evidence now is gravitation waves, though lord, not for a lack of trying. You think GB-P has problems with noise? Go read up on the history of LIGO, the Laser Interferometer Gravitational-wave Observatory, called (only slightly saracastically) the greatest noise detector mankind has ever built.
I thought it went "Assuming a perfectly spherical cow..."
...of uniform density and no charge....
posted by eriko at 3:11 PM on May 4, 2011 [2 favorites]
Because there had never been direct confirmation of geodetic precession or frame dragging in GR before -- there were measurements that had such large errors that they really couldn't confirm the theory. Some of them seemed more likely to disprove than prove, but once again, the errors were huge -- the signal they were looking for by theory is incredibly small. Kip Thorne described it thus: "In the realm of black holes and the universe, the language of general relativity is spoken, and it is spoken loudly. But in our tiny solar system, the effects of general relativity are but whispers."
GP-B has basically nailed down geodetic precession, and has come pretty close to nailing down frame dragging. Really, the only prediction of GR that doesn't have direct experimental evidence now is gravitation waves, though lord, not for a lack of trying. You think GB-P has problems with noise? Go read up on the history of LIGO, the Laser Interferometer Gravitational-wave Observatory, called (only slightly saracastically) the greatest noise detector mankind has ever built.
I thought it went "Assuming a perfectly spherical cow..."
...of uniform density and no charge....
posted by eriko at 3:11 PM on May 4, 2011 [2 favorites]
Basic question: Is this because the earth is spinning, or because the earth is spinning and is not uniform with respect to gravity (i.e. different densities at different spots, not a sphere, et cetera)?
posted by Flunkie at 3:35 PM on May 4, 2011
posted by Flunkie at 3:35 PM on May 4, 2011
There were other problems with the data - so much so, that NASA pulled funding from the data analysis in 2008. The Saudi Royal Family stumped up nearly all of the $3.2 million required to finish the job...
posted by Devonian at 4:36 PM on May 4, 2011
posted by Devonian at 4:36 PM on May 4, 2011
Eriko - given that the satellite was tracking one of the four gyros to within a nanometre and using microthrusters to maintain alignment of the craft wrt the gyros, how did it realign itself without making the balls crash? If there was just one ball, the spacecraft could realign itself around that, but I can't see what then happens to the other three.
posted by Devonian at 4:48 PM on May 4, 2011
posted by Devonian at 4:48 PM on May 4, 2011
They developed a "drag free" satellite that could brush against the outer layers of Earth's atmosphere without disturbing the gyros. They figured out how to keep Earth's magnetic field from penetrating the spacecraft. And they created a device to measure the spin of a gyro--without touching the gyro.
They're not just banging rocks together here, they know how to detect a space-time vortex.
posted by The Winsome Parker Lewis at 5:57 PM on May 4, 2011 [2 favorites]
They're not just banging rocks together here, they know how to detect a space-time vortex.
posted by The Winsome Parker Lewis at 5:57 PM on May 4, 2011 [2 favorites]
Basic question: Is this because the earth is spinning, or because the earth is spinning and is not uniform with respect to gravity (i.e. different densities at different spots, not a sphere, et cetera)? It's fundamentally due to the spin of the Earth. Even if Earth was as smooth as the gyros they were using, there would still be an effect.
Gravity Probe B is one of those projects that I've heard about for my entire scientific career (which, granted, is not as long as that might sound) and which, given the litany of problems that it's experienced, I honestly did not expect to actually get useful results. An example of their problems and resourcefulness: NASA pulled the plug on the funding for the data analysis in 2008, but the project leaders managed to convince the King Abdulaziz City of Science and Technology to fund them instead.
This gives me hope that one day we'll see results from LISA after all.
posted by Johnny Assay at 6:23 PM on May 4, 2011
Gravity Probe B is one of those projects that I've heard about for my entire scientific career (which, granted, is not as long as that might sound) and which, given the litany of problems that it's experienced, I honestly did not expect to actually get useful results. An example of their problems and resourcefulness: NASA pulled the plug on the funding for the data analysis in 2008, but the project leaders managed to convince the King Abdulaziz City of Science and Technology to fund them instead.
This gives me hope that one day we'll see results from LISA after all.
posted by Johnny Assay at 6:23 PM on May 4, 2011
Pardon my poor physics, but how does this prove spaceTIME -- what is the time element of this experiment? To me this reads "Gravity pulls gyroscope off axis".
posted by blargerz at 7:05 PM on May 4, 2011
posted by blargerz at 7:05 PM on May 4, 2011
I understand the experiment would have been impossible were the balls not floating in vessel containing 99.9999% pure "Tang."
posted by digsrus at 7:27 PM on May 4, 2011
posted by digsrus at 7:27 PM on May 4, 2011
Funny, I was just going to post an ASKMeFi about what our time dilation was due to the Earth's movement around the Sun and in the Milky Way...
I mean, how can we expect to life on other planets if we're slowed down in here?
posted by CarlRossi at 9:44 PM on May 4, 2011
I mean, how can we expect to life on other planets if we're slowed down in here?
posted by CarlRossi at 9:44 PM on May 4, 2011
This looks like an amazing result. Something I've never understood though is why the dimple in space-time is pointing down. Is that just a simplification of the model so that people can visualize it? Is there a dimpling in all directions? [In similar fashion, I've always wondered why the earth gets depicted as having a top and a bottom.]
No dimple/ bottom jokes.
posted by rudster at 12:02 AM on May 5, 2011
No dimple/ bottom jokes.
posted by rudster at 12:02 AM on May 5, 2011
Something I've never understood though is why the dimple in space-time is pointing down. Is that just a simplification of the model so that people can visualize it?
Exactly yes. The "rubber sheet" diagrams of curved space show space as a 2-dimensional surface embedded in a 3-dimensional space, but that's just to make it easier to visualize. Even though 4-dimensional spacetime is curved, there's no theoretical need for it to be embedded in some higher-dimensional uncurved space: curvature is something you can measure entirely within the space. The curvature around a (smooth, nonrotating, etc) body is symmetric in all directions, there isn't a "down".
The rubber-sheet model also misleadingly suggests that gravity pulls things into the dimple because the dimple points down, kind of requiring a metagravity by which gravity operates. That's not true, objects' motion is entirely due to the shape of the sheet, though to fully describe it requires that time, like space, is curved and visualizing that is even trickier.
(Some theories do postulate a higher-dimensional space in which our universe is a membrane, but that's much more speculative stuff than GR curvature.)
posted by hattifattener at 12:38 AM on May 5, 2011
Exactly yes. The "rubber sheet" diagrams of curved space show space as a 2-dimensional surface embedded in a 3-dimensional space, but that's just to make it easier to visualize. Even though 4-dimensional spacetime is curved, there's no theoretical need for it to be embedded in some higher-dimensional uncurved space: curvature is something you can measure entirely within the space. The curvature around a (smooth, nonrotating, etc) body is symmetric in all directions, there isn't a "down".
The rubber-sheet model also misleadingly suggests that gravity pulls things into the dimple because the dimple points down, kind of requiring a metagravity by which gravity operates. That's not true, objects' motion is entirely due to the shape of the sheet, though to fully describe it requires that time, like space, is curved and visualizing that is even trickier.
(Some theories do postulate a higher-dimensional space in which our universe is a membrane, but that's much more speculative stuff than GR curvature.)
posted by hattifattener at 12:38 AM on May 5, 2011
Threads like these are why I come to MetaFilter: smart people making sense of the amazingly 'above-my-head.' I've never been shy about what I do not know. Now I know a little more.
posted by NationalKato at 8:36 AM on May 5, 2011 [1 favorite]
posted by NationalKato at 8:36 AM on May 5, 2011 [1 favorite]
My non-geek friends and family often ask me about these bits of science news, wondering why we (taxpayers) fund them to find some obscure pointless result. I generally take the field in question (particle physics, molecular biology, etc.) and try to explain something familiar, like an MRI machine or DNA identification, then point out that perhaps experiment X will yield something awesome down the road.
In this case, the explanation was easy: GPS wouldn't work unless we understood a lot about relativity to correct its timing differences. In a Newtonian world, your phone couldn't tell you how to get to Starbucks. (Not that we need to correct GPS timing for the miniscule effects of frame-dragging, but the greater point is useful, I think.)
posted by introp at 9:44 AM on May 5, 2011
In this case, the explanation was easy: GPS wouldn't work unless we understood a lot about relativity to correct its timing differences. In a Newtonian world, your phone couldn't tell you how to get to Starbucks. (Not that we need to correct GPS timing for the miniscule effects of frame-dragging, but the greater point is useful, I think.)
posted by introp at 9:44 AM on May 5, 2011
But the GP-B team pulled a clever.
Where I come from we call this weighing the bag and it's hardly clever.
posted by Civil_Disobedient at 10:20 AM on May 5, 2011 [1 favorite]
Where I come from we call this weighing the bag and it's hardly clever.
posted by Civil_Disobedient at 10:20 AM on May 5, 2011 [1 favorite]
"The mass of Earth dimples this fabric, much like a great big fat person sitting in the middle of a trampoline," according to Prof. Buffalo Bill of Our Lady of the Lamb College.
posted by Eideteker at 11:27 AM on May 9, 2011
posted by Eideteker at 11:27 AM on May 9, 2011
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posted by Uther Bentrazor at 11:41 AM on May 4, 2011 [3 favorites]