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/sci/ - Science & Math


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3496120 No.3496120 [Reply] [Original] [archived.moe]

This image describes a theory of how gravity works.

The larger mass warps the fabric of space time, causing the smaller body to "roll" down the slope thus being pulled towards the larger body.

Isn't this inherently wrong though since the only reason things roll down the slope is because of gravity in the first place? It is like using a word in its own definition.

>> No.3496136

It's an ANALOGY.

>> No.3496138

You're thinking Euclidean. The geometry of the universe is more complicated

>> No.3496140
File: 35 KB, 692x313, teaching_physics.png [View same] [iqdb] [saucenao] [google] [report]
3496140

>> No.3496146

>>3496136
I know that. It's what I have an issue with.

>> No.3496158

>>3496146
Deal with it.

Things like these are meant to explain phenomena to stupid people with no knowledge of math. Don't like it? Learn math and write down Einstein's field equations.

>> No.3496159
File: 32 KB, 740x308, applied.png [View same] [iqdb] [saucenao] [google] [report]
3496159

>>3496140
where are these comics from? they are amazing but i only see them on 4chan

>> No.3496160
File: 15 KB, 320x260, cast.jpg [View same] [iqdb] [saucenao] [google] [report]
3496160

>>3496136
heh heh you said anal

>> No.3496167

>>3496159
xkcd. I find most of them are shitty personally.

>> No.3496168

>>3496159
xkcd.com

OP:
It's a layman's analogy, designed for the common man. If you really want to understand what's going on, learn physics

>> No.3496169

>>3496159
xkcd.com

>> No.3496171

>>3496120
I made this thread yesterday with no replies

From my understanding it only makes sense mathematically

But yes, it's like saying electricity is like a stream of electrons flowing through a materical and calling it an analogy

>> No.3496173
File: 55 KB, 740x312, certainty.png [View same] [iqdb] [saucenao] [google] [report]
3496173

>>3496159

>> No.3496175

>>3496171
But that is an analogy. Electricity isn't ACTUALLY water

>> No.3496178

>>3496173
this shit is golden

>> No.3496191

No. Take a one-dimensional example:

Make a spacetime diagram of two objects initially at rest and some distance apart. The diagram just looks like two vertical lines. Now, if the surface of the diagram is curved, it's impossible to draw the lines parallel - by drawing the geodesic (shortest path through the the curved space) the two lines eventually intersect.

>> No.3496192

I made a thread like this a long time ago OP. Got the same replies as you. The general consensus is that it's a completely stupid analogy which doesn't make any logical sense if you think about at all.

It's used in a huge amount of shows about space and shit though, you wouldn't believe how common it is.

>> No.3496199

>>3496192
That's not true. It makes lots of sense.

See >>3496191

>> No.3496201

SMBC > xkcd

>> No.3496225

>>3496201
Amen.

>> No.3496237

>>3496191
This entirely blew my mind, thank you /sci/

>> No.3496238
File: 179 KB, 800x600, 1288648981465.jpg [View same] [iqdb] [saucenao] [google] [report]
3496238

this is now a comic thread

>> No.3496249
File: 36 KB, 150x153, Fig_8_2[1].jpg [View same] [iqdb] [saucenao] [google] [report]
3496249

Continuing from >>3496191

The red lines on this picture are geodesics. Pretend this is the spacetime diagram, time on the vertical axis and position on the horizontal. You can see that the two objects accelerate toward each other.

Draw the same diagram on a flat piece of paper - you just get two parallel lines that extend off to infinity.

>> No.3496251

Well now I feel dumb. I was having a discussion about gravity with a friend, and mentioned that we don't know how gravity works. My friend responded that it's the curvature in space time, and I took that for true. Time for another science talk.

>> No.3496252

>>3496238
Oh yai, philosophy with cute animals. whats link to that comic?

>> No.3496254

The point of the analogy is not to show that an object will roll to the dent. It is to show that what was traveling in a straight line will now deflect.

>> No.3496260

>>3496252
http://nedroid.com/
most awesomest comic on the interwebs

>> No.3496264

>>3496251
Don't worry, the kind anon in >>3496191 and >>3496249 helped you out.

>> No.3496267

>>3496251
gravity causes the curvature of space time.

>> No.3496277

>>3496254
Exactly right. I guess these science documentaries don't do a good job of actually explaining the analogy.

>> No.3496290
File: 149 KB, 861x628, 1284530401155.jpg [View same] [iqdb] [saucenao] [google] [report]
3496290

yay comics

>> No.3496297
File: 358 KB, 859x1349, 2010-08-05-TheBigConference.jpg [View same] [iqdb] [saucenao] [google] [report]
3496297

>> No.3496299

>>3496267
No it doesn't. An object's energy-momentum causes the curvature, and objects follow this curved spacetime. The whole interaction is labeled as gravity.

>> No.3496307
File: 56 KB, 1206x394, fields.jpg [View same] [iqdb] [saucenao] [google] [report]
3496307

>>3496159

>> No.3496312

>>3496299
In other words, gravity causes the curvature of space time.

>> No.3496315

>>3496312
No, gravity IS the curvature of spacetime.

>> No.3496356

>>3496315
I don't know about you but what bothers me the most on gravity is how to compute the energy of gravitational wave emission generated by photon as a function of time and energy of the photon (or in a simpler way to write down energy of a photon as a function of time).
It should be something of this form:
E_t1 = E_t0[exp(t/τ)]
where E_t0 is energy of photon when emitted,
τ is time constant - this is the bit which I don't know how to compute.
Any ideas on how to compute it?
Many thanks.

>> No.3496358
File: 132 KB, 725x275, 1307084704214.jpg [View same] [iqdb] [saucenao] [google] [report]
3496358

>>3496315

ITT: people fail at interpreting science

more comics

>> No.3496369
File: 54 KB, 735x500, comic2-949.png [View same] [iqdb] [saucenao] [google] [report]
3496369

>>3496260
second most

>> No.3496376

> complaints that a fundamental force is explained in terms of itself
> fundamental force
> fundamental

>> No.3496428
File: 56 KB, 735x500, comic2-638.png [View same] [iqdb] [saucenao] [google] [report]
3496428

This is my favorite Dinosaur Comic. It has found use in many threads on this board.

>> No.3496442

>>3496307
They are all philosophy, you tard.

>> No.3496445

>>3496376
Read the thread, you dunce.

>> No.3496493

>>3496445
Why don't you read the thread next time?

Seriously, I hate you this much right now.

>> No.3496497

>>3496493
How much?

I did read the thread. One anon answered OP very well, without resorting to "well hurr durr it's fundamental derp"

>> No.3496526

>>3496299
>An object's energy-momentum causes the curvature
so something travelling faster attracts more ?

>> No.3496552

>>3496526
http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor

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