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Experiments Reveal That Deformed Rubber Sheet Is Not Like Spacetime

Unknown Lamer posted about 4 months ago | from the deformed-example dept.

Science 264

KentuckyFC writes "General relativity is mathematically challenging and yet widely appreciated by the public. This state of affairs is almost entirely the result of one the most famous analogies in science: that the warping of spacetime to produce gravity is like the deformation of a rubber sheet by a central mass. Now physicists have tested this idea theoretically and experimentally and say it doesn't hold water. It turns out that a marble rolling on deformed rubber sheet does not follow the same trajectory as a planet orbiting a star and that the marble's equations of motion lead to a strangely twisted version of Kepler's third law of planetary motion. And experiments with a real marble rolling on a spandex sheet show that the mass of the sheet itself creates a distortion that further complicates matters. Indeed, the physicists say that a rubber sheet deformed by a central mass can never produce the same motion of planet orbiting a star in spacetime. So the analogy is fundamentally flawed. Shame!"

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264 comments

The earth orbits the sun... (2, Funny)

Anonymous Coward | about 4 months ago | (#45882993)

like a car looking for a parking place.

Re:The earth orbits the sun... (1)

Tablizer (95088) | about 4 months ago | (#45883121)

like a car looking for a parking place.

Hopefully like the CA Bay Area, otherwise we'll eventually find a spot and bake to death, AZ parking style.

In soviet rubber (1, Funny)

Anonymous Coward | about 4 months ago | (#45882995)

Space time bends you!

true. (-1)

Anonymous Coward | about 4 months ago | (#45882997)

it is like a car.

Um... (5, Insightful)

MightyMartian (840721) | about 4 months ago | (#45883007)

I'm not sure the analogy was ever meant to be a rigorous and exact model, but more of a kind of way of visualizing space-time. All analogies break down if you try to map them exactly to the phenomenon you're trying to explain. After all, it's an analogy, not a model.

Re:Um... (2, Insightful)

joe_frisch (1366229) | about 4 months ago | (#45883063)

I have never like it as an analogy either. In the classic classroom rubber-sheet demonstration the marble rolls toward the bowling ball because the EARTH's gravity causes it to roll down hill. This is nothing at all like the way general relativity works.

General relativity requires a curvature of space-time, not just space. The best analogy I've seen comes from Kip Thorne (I think); Imagine 2 ants on the surface of an orange, both walking towards the "north" pole. Walking is an analogy to moving forward in time. After a while some "force" has brought them closer together (because they are near the pole).

Re:Um... (1)

noh8rz10 (2716597) | about 4 months ago | (#45883251)

what exactly did the experimental physicists test? did they test the behavior of marbles on rubber sheets? science is awesome!

I like it as an analogy because it captures the "gravity well" idea pretty good. also, I don't understand that ant thing at all.

Re:Um... (4, Interesting)

joe_frisch (1366229) | about 4 months ago | (#45883387)

The dented rubber sheet (done in earth's gravity) is a not too bad analogy for Newtonian gravity.

Let me try the "ant" analogy in a bit more detail:

The "orange" is curved space time. here we have 1 space like dimension and one time like dimension, curved into 3d.
The "ants" walk forward. This walking is the analogy to moving forward in time.

On a big flat surface, two ants that started near each other walking on parallel paths (both moving forward in time and at rest relative to each other) would stay the same distance apart.

On the curved orange though as the ants walk forward, they wind up getting closer: Imagine they start at the equator and both head due north. The start out parallel, and both walk in as straight a line as is possible on the surface. After a while they find themselves closer together - as if some mysterious force (gravity) is attracting them. (this is as they get to the north pole.

The orange analogy isn't all that great either because the curvature isn't shaped right for GR. Unfortunately humans aren't good at imagining curved 4-dimensional space.

If the rubber-sheet demo is done without earth's gravity it isn't a terrible analogy, but I don't think I've ever seen it show that way. It seems to always be shown as this curved surface where the EARTH's gravity causes the marbles to roll to the center.

 

Re:Um... (5, Informative)

Anonymous Coward | about 4 months ago | (#45883767)

If the rubber-sheet demo is done without earth's gravity it isn't a terrible analogy, but I don't think I've ever seen it show that way. It seems to always be shown as this curved surface where the EARTH's gravity causes the marbles to roll to the center.

If it's done without the Earth's gravity then nothing happens, the ball just fucking sits there, and nothing makes a "dent" in the rubber because... there's no gravity.

It's an analogy, not a physical model. You're supposed to ignore the presence of Earth's gravity when you look at it, and understand that the way the balls deform the surface is in some respects similar to how an object deforms space-time.

I can't say this enough: An ANALOGY is not the same thing as a MODEL. It's not supposed to be a physically accurate representation, you should NOT expect to roll a ball across the surface and get results that match actual real-world physics. That's why we call it an ANALOGY.

Re: Um... (1)

MrNaz (730548) | about 4 months ago | (#45883967)

That analogy is useful, however with the rubber sheet example there is the force to time misrepresented analogy. That ant example is just changes the time analogy to bring motion rather than force, and is also flawed thus. There really isn't a way to understand relativity without, well, understanding relativity.

Not that I have any idea what I'm taking about.

Re:Um... (1)

Anonymous Coward | about 4 months ago | (#45883307)

You misunderstand the analogy. Even if the marble doesn't roll "downhill" due to gravity, it till still follow a curved path because the rubber sheet is curved. A straight line along the curved sheet (which a massless marble would follow) is not a straight line in Cartesian coordinates.

Re:Um... (1)

joe_frisch (1366229) | about 4 months ago | (#45883339)

I agree, the marble will still follow a curve if it sticks to the rubber in zero-g - so the curvature does change its trajectory. Usually when this is shown though ,it is done in earth gravity and that is the largest effect on the marble. Even in zero-g, the analogy with GR is very thin because the curvature of the rubber sheet doesn't involve the time coordinate, so the effect on the marble's path doesn't really look like gravity in GR.

Done right the rubber sheet can be a barely OK analogy, as it is usually done though it is just confusing.

Re:Um... (3, Interesting)

nashv (1479253) | about 4 months ago | (#45883351)

In the analogy of the rubber sheet, the earth's gravitational acceleration is the passage of time.

Re:Um... (1)

Anonymous Coward | about 4 months ago | (#45883551)

I have never like it as an analogy either. In the classic classroom rubber-sheet demonstration the marble rolls toward the bowling ball because the EARTH's gravity causes it to roll down hill. This is nothing at all like the way general relativity works.

General relativity requires a curvature of space-time, not just space. The best analogy I've seen comes from Kip Thorne (I think); Imagine 2 ants on the surface of an orange, both walking towards the "north" pole. Walking is an analogy to moving forward in time. After a while some "force" has brought them closer together (because they are near the pole).

In the "rubber sheet" analogy, rolling the ball is the same thing as the ant walking in yours.
More to the point, it's an ANALOGY. It's not a model, it's not a representation, it's a visual aid used to help get the general idea across to people with limited technical understanding of what's actually going on.

It's not going to match up with reality, it was never supposed to. Just like talking about the internet as a "highway" or "pipes" has almost no resemblance at all to a real network. The higher-level concept is what the analogy is trying to get across, and for that it works just fine.

Re:Um... (1)

LordKronos (470910) | about 4 months ago | (#45883629)

I have never like it as an analogy either. In the classic classroom rubber-sheet demonstration the marble rolls toward the bowling ball because the EARTH's gravity causes it to roll down hill. This is nothing at all like the way general relativity works.

General relativity requires a curvature of space-time, not just space. The best analogy I've seen comes from Kip Thorne (I think); Imagine 2 ants on the surface of an orange, both walking towards the "north" pole. Walking is an analogy to moving forward in time. After a while some "force" has brought them closer together (because they are near the pole).

And yet, to someone like me (a non-physicist) the rubber sheet analogy makes a lot of sense to me, while the orange analogy....well, I'm not exactly sure where you are going with that because it helps me understand nothing. Maybe you just didn't explain it fully or correctly, but I'm not finding it very useful

Re:Um... (4, Insightful)

bloodhawk (813939) | about 4 months ago | (#45883067)

I'm not sure the analogy was ever meant to be a rigorous and exact model, but more of a kind of way of visualizing space-time. All analogies break down if you try to map them exactly to the phenomenon you're trying to explain. After all, it's an analogy, not a model.

^this, many analogies in science are made to give a layperson a general/basic understanding of the concepts at work. They were never meant to be or expected to be working mathematical models.

Re:Um... (1)

TeknoHog (164938) | about 4 months ago | (#45883125)

Yup, I always thought the model is a little dumb, because it needs a gravitational field perpendicular to the sheet to actually get deformed.

Re:Um... (1)

mdielmann (514750) | about 4 months ago | (#45883205)

Ah, so you too don't know the difference between a model and an analogy. In your car "model" of a Linux computer, what counts as the wheels?

Re:Um... (0)

Anonymous Coward | about 4 months ago | (#45883329)

Nah, you could get a similar effect in zero-g by putting a marble in between 2 taught rubber sheets.

BadAnalogyGuy (0)

Anonymous Coward | about 4 months ago | (#45883137)

Where is he when you need him??

Re:BadAnalogyGuy (0)

Anonymous Coward | about 4 months ago | (#45883241)

He's like not here.

Re:Um... (1)

Anonymous Coward | about 4 months ago | (#45883177)

Besides, the theoretical model is a frictionless and massless rubber sheet, not a real rubber sheet.

Re:Um... (1, Troll)

Jane Q. Public (1010737) | about 4 months ago | (#45883521)

Besides, the theoretical model is a frictionless and massless rubber sheet, not a real rubber sheet.

Physicists getting paid (likely tax money, too) for playing with marbles, to show that an analogy is only... an analogy.

I think I want that job.

Re:Um... (1)

msauve (701917) | about 4 months ago | (#45883213)

This just in... frictionless pucks don't exist either, and collisions in the real world don't perfectly maintain momentum.

This is old news (5, Informative)

Anonymous Coward | about 4 months ago | (#45883009)

This was figured out more than 100 years ago. A rubber sheet can be mapped to a scalar theory of gravity. If you made it past the first two lectures of a class on General Relativity, you would know that Relativity is a tensor theory. That is why it is so horrendously complicated.

Re:This is old news (1)

Em Adespoton (792954) | about 4 months ago | (#45883033)

This was figured out more than 100 years ago. A rubber sheet can be mapped to a scalar theory of gravity. If you made it past the first two lectures of a class on General Relativity, you would know that Relativity is a tensor theory. That is why it is so horrendously complicated.

Maybe they should be using a tensor bandage instead of a rubber sheet then? :D

If you have a better idea ... (1)

cgoodric (1311355) | about 4 months ago | (#45883011)

It's probably the closest and most easily understood real-world analogy you're going to get.

Re:If you have a better idea ... (0)

Anonymous Coward | about 4 months ago | (#45883049)

How about an analogy containing a pair of trousers?

Re:If you have a better idea ... (0)

Anonymous Coward | about 4 months ago | (#45883135)

Well we all understand the Trousers of Time, Archchancellor, but I don't see what that has to do with the Bursar and a rubber sheet?

Re:If you have a better idea ... (0)

Anonymous Coward | about 4 months ago | (#45883381)

I'm all ears.

Re:If you have a better idea ... (0)

Anonymous Coward | about 4 months ago | (#45883707)

No good, most people don't have a good grasp of Trouser Calculus.

That's new? (0)

Anonymous Coward | about 4 months ago | (#45883013)

I thought that would have been known by now.
Call me a troll if you like, but this is not exactly a revelation or news in any form to me.

and there is no santa claus (0)

Anonymous Coward | about 4 months ago | (#45883017)

for shame!

Thought experiments (3, Insightful)

cold fjord (826450) | about 4 months ago | (#45883019)

Thought experiments using analogues like the rubber sheet are often useful for visualization, organizing your thoughts, or providing a template to work on, but that doesn't mean that they necessarily provide a picture that is correct in all respects. The fact that they aren't accurate in all respects doesn't mean that they aren't useful representations.

Somebody shit the bed on this one... (1)

Anonymous Coward | about 4 months ago | (#45883021)

Let's come up with a real complicated illustration for laymen to explain how space time might work. Perhaps a ladybug in a drinking fountain or something.

Works for the public (3, Insightful)

BringsApples (3418089) | about 4 months ago | (#45883025)

Maybe it's just a general analogy for general relativity that's easy to understand, and not to be taken so so literally. Did they bother to come up with another analogy? Didn't think so. What dicks.

Old News (0, Redundant)

Anonymous Coward | about 4 months ago | (#45883029)

This was figured out more than 100 years ago. A rubber sheet can be mapped to a scalar theory. However, as anyone who has made it past the first two lectures of a course on General Relativity would know, Relativity is a tensor theory. That is why it is so horrendously complicated.

I don't think .... (5, Insightful)

therealkevinkretz (1585825) | about 4 months ago | (#45883031)

... that anyone who had a grasp of high school phsyics, and who understood the analogy - of 3D matter flattened to represent a 2D metaphor for our real 3D world, which lives in 4D spacetime - or who understood that gravity attracted mass towards mass and not towards the "down" direction perpendicular to the sheet - would think for a second that such a demonstration would create the same exact trajectory as actual interaction between 3D objects in 4D spacetime.

Re:I don't think .... (4, Insightful)

avandesande (143899) | about 4 months ago | (#45883171)

I don't think the scientists did either- I think this was more of a 'fun' experiment to see what happens when you actualize the analogy.

Re:I don't think .... (1)

Anonymous Coward | about 4 months ago | (#45883317)

... that anyone who had a grasp of high school phsyics

The number of high school students who truly understand (as opposed to memorized facts about) what you call "high school physics" is absolutely minuscule, so I think calling it "high school physics" is a bit misleading.

Stupid (3, Insightful)

Anonymous Coward | about 4 months ago | (#45883037)

No analogy is perfect. However relativity is sufficiently complex that I don't know if any analogy would be perfect at all. This analogy at least provides a general sense of the way it works, it may not be 100% accurate but's relatively (see what I did there) close enough to provide a general understanding.

Why did they bother? (3, Interesting)

AbsoluteXyro (1048620) | about 4 months ago | (#45883039)

Who seriously expected the physics of a marble rolling on a rubber sheet to exactly match the physics of a planetary body in orbit? Who thought the analogy was ever meant to make that statement? It's still a pretty good analogy for giving a layperson the gist of how gravity works, and I seriously doubt it was ever meant to do any more than just that.

Re:Why did they bother? (1)

fido_dogstoyevsky (905893) | about 4 months ago | (#45883357)

Who seriously expected the physics of a marble rolling on a rubber sheet to exactly match the physics of a planetary body in orbit? Who thought the analogy was ever meant to make that statement? It's still a pretty good analogy for giving a layperson the gist of how gravity works, and I seriously doubt it was ever meant to do any more than just that.

So in class I can still use a room full of mousetraps loaded with ping pong balls as an analogy for a nucular chain reaction?

Flawed, but not useful? (3)

steelfood (895457) | about 4 months ago | (#45883045)

All analogies are flawed in some way. They're analogies. They're not the actual thing. If the rubber sheet's characteristics match that of spacetime exactly, it probably is spacetime.

But even if it's not exact, I think it's still a useful way to illustrate to the general relativity-illiterate (yours truly being among them) what the theory is all about, and why it's significant. General relativistic effects are not something that can be demonstrated (easily) in the classroom. Putting a marble on a rubber sheet is.

Re:Flawed, but not useful? (4, Funny)

Darinbob (1142669) | about 4 months ago | (#45883273)

Analogies are like rubber sheets in that they have to be deformed to match their models.

Whiskey. Tango. Foxtrot. (1)

mmell (832646) | about 4 months ago | (#45883051)

Uh, that whole 'spacetime is like a rubber sheet' thing was just a bad metaphor used to attempt to explain the (relativistic) effect of mass on the 'shape' of space. I don't recall ever seeing studies on the effects of vulcanizing on the elasticity of space (cue the Star Trek jokes). Think about it - using gravity to explain gravity? That sounds like teching the tech to me.

Re:Whiskey. Tango. Foxtrot. (0)

Anonymous Coward | about 4 months ago | (#45883151)

The rubber sheet analogy isn't using gravity to explain gravity. The marble goes into the divot in the sheet not because it's lower and therefore pulled in there by gravity, but because the surface of the sheet is curved.

If you had a "sticky marble" and took the rubber sheet into orbit and deformed it, the marble would still curve toward the divot. Not because gravity pulls it there but because the sheet is curved. That's the whole point of the analogy.

To think that the "real" gravity acting from outside is what causes the marble to curve its path is to misunderstand the analogy.

Re:Whiskey. Tango. Foxtrot. (1)

GigaplexNZ (1233886) | about 4 months ago | (#45883217)

So what if the sheet is curved? Banking on a race track corner works due to gravity, not because of the shape of the curve.

Re:Whiskey. Tango. Foxtrot. (1)

Anonymous Coward | about 4 months ago | (#45883801)

Wrong, kind of. Yes a bit and no a bit.

Think about a 90 degree bank. Or a loop. Or a motorbike in a sphere of death (with a bike with magnetic tyres in free fall with no gravity) . They work in spite of gravity or the lack of. More to do with Centripetal acceleration than gravity for example.

Which is kind of what space time is talking about, its the shape of space that bends the path.

  But you should explain this while you are using your flawed analogy. Explain why its flawed. Teaching physics is less like teaching and telling someone facts as it is hypnotising them and talking about zen like questions to use confusion to further understanding of a concept or principle. Here look at this tennis ball go near to the bowling ball on the rubber mat. Lets see if we can make a gravitational slingshot happen and make the tennis ball travel faster. How is that possible? Do photons exist if they aren't observed? Cat is in a box is it alive/dead? What's the biggest thing that can be alive dead? If photons have no mass why does gravity affect them? What is mass? What is gravity?

  Then you guide them on their journey of introspective self discovery. They should end up with a Feynman like state of uncertainty where they aren't really sure about anything and know they know nothing about a lot of things. They should have a blank look of deep thought and a 1000 mile stare on their faces. Then you explain they only have read the first letter of a 1000 km thick book about physics, and that first character is a word that tries to start of explaining an approximation of what physics is.

I hate having people tell me how to teach. In my state we have a dot point that says "use the water analogy to teach electricity". Most teachers say water = electricity and thats that. They don't understand themselves the limitation of the water analogy. Then they write a test to see if the student has memorised a fact which is wrong.

  Physics isn't like chemistry or Biology or history or any other stamp collecting subject. Its not even like mathematics. Memorising physics facts will get you nothing.

  Physics you should come out a bit confused and not sure of anything, because really, you can't be sure of anything, just a level of confidence of what you are observing.

Re:Whiskey. Tango. Foxtrot. (0)

Anonymous Coward | about 4 months ago | (#45883943)

Banking on a race track corner works due to gravity, not because of the shape of the curve.

Gravity is pretty much the same everywhere on Earth. Racetracks have different curve shapes. Your hypothesis seems flawed. Inertia is probably a better answer as to why banking works.

Analogy vs Model (4, Informative)

EdmundSS (264957) | about 4 months ago | (#45883055)

No. A rubber sheet is a flawed *model* for the shape of spacetime; as an *analogy*, it's still reasonable...

All analogies are fundamentally flawed (5, Interesting)

Koen Lefever (2543028) | about 4 months ago | (#45883059)

Analogies help to understand something... up to a certain point.

It only illustrates the basic concepts. After that, one has to go beyond the analogy and do the math.

I remember a poster on a door at the math department of my university (parafrazing from memory): "Do not try to visualize a space with more than 3 dimensions. Nobody can do that, trying will just twist your mind. Just use the formulas with the correct number of variables and leave it at that."

It's an analogy for lay people... (1)

Hellbuny (444564) | about 4 months ago | (#45883065)

So that lay people can wrap their head around a very hard concept. One would think that this would be clearer to the person who wrote the paper. And if they offered an analogy that was as easy to use as an entry point to this very complex set of concepts, they would come off less as d-bags.

Re:It's an analogy for lay people... (1)

Anonymous Coward | about 4 months ago | (#45883285)

Lay people can't wrap their pathetic little heads around very hard concepts such as this. Flawed analogies just give them a flawed 'understanding,' which makes the whole ordeal useless.

For Pete's Sake! (5, Funny)

Tablizer (95088) | about 4 months ago | (#45883077)

Next they are gonna to tell me my Fisher Price bath boats are not sufficient for planning naval invasions.

Re:For Pete's Sake! (1)

Anonymous Coward | about 4 months ago | (#45883131)

Of course not, don't be silly. Now Lego, that's another matter entirely. Lego is the stuff of military dominance!

Re:For Pete's Sake! (1)

jc42 (318812) | about 4 months ago | (#45883201)

Next they are gonna to tell me my Fisher Price bath boats are not sufficient for planning naval invasions.

Of course not, don't be silly. Now Lego, that's another matter entirely. Lego is the stuff of military dominance!

So we should be watching Denmark very closely ...

Re:For Pete's Sake! (1)

Anonymous Coward | about 4 months ago | (#45883165)

Welcome to Slashdot, Mr. Bush!

This article is troll (1, Insightful)

BringsApples (3418089) | about 4 months ago | (#45883085)

From TFA:

But the truth is that this work cannot diminish the extraordinary utility of this analogy. And so the public love affair with general relativity is safe. Long may it continue!

So what's the damn point?

"So what's the damn point?" (0)

Anonymous Coward | about 4 months ago | (#45883195)

Funding for tenured physics professors.

Rubber sheet analogy explained (5, Funny)

Anonymous Coward | about 4 months ago | (#45883087)

Suppose that you had a big rubber sheet stretched out, and onto that sheet you place a ball. Now suppose that there's a force that pulls the ball down, creating a depression in the sheet. Well, gravity is a lot like that force. Really a lot like it.

spacetime has more than two dimensions (0)

Anonymous Coward | about 4 months ago | (#45883089)

A deformed rubber sheet is a two dimensional simplification. Of course it's inadequate.

You forgot to add the dark matter (1)

WillAffleckUW (858324) | about 4 months ago | (#45883091)

Obviously it's not like space-time.

You forgot to add the Dark Matter.

It's in the third shelf from the left.

Attack the Slashdot summary, not the article (2)

MobyDisk (75490) | about 4 months ago | (#45883099)

So the analogy is fundamentally flawed. Shame!

The analogy is not fundamentally flawed. The Slashdot summary is. There is nothing wrong with doing this kind of test, it's kind of "mythbusters" semi-science. It's kinda nifty. The problem, as usual, is the over-reporting of science in an attempt to create pithy quotable summaries.

The experts have spoken (3, Interesting)

steveha (103154) | about 4 months ago | (#45883103)

In other news, experts pointed out that rubber sheets provide a two-dimensional surface, while the real spacetime continuum provides three spatial dimensions and one of time. Experts also pointed out that rubber sheets have nonzero friction with rolling marbles, while empty space has zero friction; and that the rubber sheets do not provide the time dilation effects that gravity provides.

Experts also pointed out that the whole rubber sheet thing is what is known as an "analogy" and pretty much by definition is inexact.

Personally, I found the article interesting, but the tongue-in-cheek "Shame!" of the summary a bit over the top.

P.S. From TFA:

But the truth is that this work cannot diminish the extraordinary utility of this analogy. And so the public love affair with general relativity is safe. Long may it continue!

That's pretty neat... (1)

katterjohn (726348) | about 4 months ago | (#45883109)

... but I'm not sure how it's a "Relativity Shock" as the second links suggests.

Upon thinking about a marble rolling on a rubber sheet I immediately see two big differences between it and a planet moving in space: (i) the marble.. well.. rolls along the sheet, which planets don't do while moving through space; and (ii) the rubber sheet doesn't propagate disturbances at the speed of light (or anywhere close to it).

I think most of us grasped this intuitively (2)

istartedi (132515) | about 4 months ago | (#45883113)

I think most of us grasped this intuitively on some level. If nothing else, a ball rolling on a sheet is always going to experience friction. It doesn't orbit. It spirals in. It's "like" relativity. Then if you get into serious physics you learn the equations that are not merely "like" but *are* relativity.

Duh... (1)

Anonymous Coward | about 4 months ago | (#45883117)

1. You have to first assume that the rubber sheet has no mass.

2. Then you have to assume some other things

3. ...

4. Profit!!!

Water Analogy (1)

Anonymous Coward | about 4 months ago | (#45883123)

Know what else? The water circuit analogy to electrical theory falls apart under scrutiny. And the easter bunny isn't real.

Obligatory XKCD (5, Informative)

Anonymous Coward | about 4 months ago | (#45883145)

Obligatory XKCD

http://xkcd.com/895/ [xkcd.com]

Re:Obligatory XKCD (1)

FuzzNugget (2840687) | about 4 months ago | (#45883389)

Woah... using an analogy containing an analogy of an analogy to explain why analogies are flawed.

Yo dawg.

massless frictionless sheet (0)

Anonymous Coward | about 4 months ago | (#45883149)

didn't you ever do those silly physics questions.

"Bobby is in a charged glider over an infinte ground plane.."

Nothing wrong with analogy... (2)

blahplusplus (757119) | about 4 months ago | (#45883157)

... when we use analogies we're dealing with the most relevant information to communicate an idea. There is certainly nothing wrong with the analogy because it was never intended to communicate the whole complexity of the phenomenon, it was always meant as a starting point.

When we use analogy we're talking in ratio's and proportion, we're saying the phenomena is a X percent like this macroscopic phenomenon that everyone knows, but of course it is more complex then that, but that's a rough approximation of what is happening.

Nobody of any intelligence should get pedantic about it because that was never the intent of the communicator to begin with. I hate these ignorant pedants that stupidly misunderstand the intent of the person who originally made the analogy. You're not being smart, you've proven you don't get anything at all about communication of complex ideas.

We 'layer' people in to understanding by giving them basic models to get across general rough approximations and then we ease them into the deeper complexities, contradictions and unknowns.

I help her drink her wine (1)

Tablizer (95088) | about 4 months ago | (#45883183)

I suppose they are going to tell my rubber girlfriend is not representative of.......naaaaah, who cares!

Idiots looking for a grade? (1)

CHIT2ME (2667601) | about 4 months ago | (#45883193)

I hope these guys get a good grade proving something which should be a no-brainer for an 8 year old. I also hope that no tax money was used in these efforts!!!

It's conceptual (1)

wjcofkc (964165) | about 4 months ago | (#45883219)

I never envisioned that the universe was literally like a rubber sheet or any object creating an indentation in a material due to its weight. But I still get the basic idea. That's the point, it communicates the basic idea in a way the average people can comprehend. Besides, most people are now exposed to this example through a computer rendered simulation, not a rubber sheet.

Its like dealing with the mythbusters (1)

Karmashock (2415832) | about 4 months ago | (#45883231)

The point of the rubber sheet analogy is to discuss the SHAPE of the surface which is a stand in for forces of gravitation.

As such, even if following the analogy you shouldn't use an actual rubber sheet because it will be distorted by the marble itself. Rather, use a hard surface modeled on what a rubber sheet would do with that deformation.

Will that be perfect? Probably not but will be less of a failure then this spandex idea.

Model (1)

Erik WP (3406995) | about 4 months ago | (#45883287)

A marble rolling on rubber is affected by a great deal more than just gravity. It's only a model, not Camelot. Next on the news: scientists find out that one dimension isn't equal to a dot and two dimensions isn't equal to a line.

analogy (0)

Anonymous Coward | about 4 months ago | (#45883337)

No shit they're different. It's an analogy, not the same thing. Of it were perfectly the same, it wouldn't be an analogy, it would be the same thing. The analogy still serves its purpose.

DUMB ARSES! (0)

Anonymous Coward | about 4 months ago | (#45883439)

What a bunch of monkeys that don't know the meaning of 'analogy'.

Completely silly. (1)

Lumpy (12016) | about 4 months ago | (#45883563)

It was used only as a visual aid to be able to teach mere mortals about gravity.

Will someone please smack these researchers, they obviously have zero social skills or understand you have to find a simple way of explaining things to the normals without their eyes glossing over and wandering away.

Everyone agrees (0)

Anonymous Coward | about 4 months ago | (#45883729)

I'm pleasantly surprised that everyone seems to have thought like me...

And that's

"Huh? It was never supposed to be an accurate model, just a way to visualize it in a rough sense. Nobody ever suggested the math would actually work out"

Doesn't Hold Water? (1)

cervesaebraciator (2352888) | about 4 months ago | (#45883739)

Now physicists have tested this idea theoretically and experimentally and say it doesn't hold water.

In my experience, rubber sheets are actually very good at holding water. I'm guessing one of these guys has a wife who, due to the number of years her husband spent on his Ph.D., is feeling the old biological clock ticking and she's taken a needle to every rubber she can find.

bending space versus gravitrons (0)

Anonymous Coward | about 4 months ago | (#45883927)

so even though the formula for gravity is the same as the formula for light intensity, we just turn a blind eye and say it is more likely that gravity is caused by a bending of an inperceivable dimension rather than there simply being gravitrons that are emitted by objects with mass?

Science centres figured this out decades ago ... (1)

MacTO (1161105) | about 4 months ago | (#45884019)

I've seen models created out of hardened plastic that more realistically reflect the curvature of space. It still isn't perfect since you still have friction, but it does a decent job of demonstrating orbits.

The true advantage of stretched rubber sheets is that it is a cheap and easy demonstration to create. That was especially important in the days before computer simulations or even television.

Only possibilities are: (1)

Ol Olsoc (1175323) | about 4 months ago | (#45884061)

Ancient Aliens!

Creationism!

All science is wrong!

Feel free to add other crap. Seriously, how many analogies are exact? An object makes a dent in time/space, and another object reacts to that dent.

Remember, the analogy is there to give an idea on how to understand space/time, not for people who already understand space /time to figure out how rubber sheets work. That's for kinky people and kids with bedwetting problems to figure out.

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