# Why gravity?

#### Andy44

##### owner: Oil Creek Astronautix
Actually - what would you accept as a valid answer to how something works if it's not math?

(genuinely curious - I think this is a difficult question, I have some ideas of my own, but I'd rather hear yours first).

Well, something akin to how I can describe how an internal combustion engine works without using any math.

But my post asking how magnets work was a reference to an internet meme; I was attempting to demonstrate through humor the fact that no matter what answer you give to the question about how gravity works, you will spawn new questions.

If I could prove to you that God exists, even that would prompt the question, "So how does the supernatural work?"

#### statickid

##### CatDog from Deimos
Donator
True, it might be considered we don't have an equation that accurately predicts humans :lol:

... Yet, here we are

#### Thorsten

##### Active member
Well, something akin to how I can describe how an internal combustion engine works without using any math.

Please humor me - how would you do that?

#### Andy44

##### owner: Oil Creek Astronautix
Please humor me - how would you do that?

Fuel and air are mixed inside a cylinder and ignited, creating hot gasses which expand, pushing a reciprocating piston attached to a rod which turns a crankshaft. The rotation of the crankshaft operates valves that allow the intake of the fuel-air mixture and the exhaust of the spent gasses.

I could go on, but you get the idea. No math is needed for a simple layman explanation. Lots of mechanics can tell you how an engine works without knowing much about the math needed to design it or perform a detailed analysis of it.

Similar to the way we describe satellite motion by analogy to a bucket swung around in your hand. The force of your hand on the bucket keeps the bucket moving around you in the same way gravity keeps a satellite moving on a curved path around a central body.

Simple concept, until you ask "but wait, how does gravity actually work?" which is the OP's question.

#### Thorsten

##### Active member
Simple concept, until you ask "but wait, how does gravity actually work?"

Let me play devils advocate here:

Fuel and air are mixed inside a cylinder and ignited, creating hot gasses which expand

But how does this actually work? Why does stuff ignite, why does ignition make anything hot (and what is heat in the first place?), and moreover, why do hot gases really expand?

So what you mean by giving an explanation here is providing a link to things we experience in daily life and hence do not question any more. We've all seen flames, so we don't really wonder how they really work. To us, the idea that hot gases expand is sort of obvious (though it wasn't through most of classic history). We know expanding stuff can push things.

In that sense, you can also explain gravity - it's the pull we feel, standing on Earth (and some of us might even have felt the lack of it during short free-fall periods). We all know what it is just as we know what a flame is or what heat is - unless we ask the question what it really is.

So I think if you take 'explanation' in the sense of 'link to stuff we know from experience', then explaining gravity affecting a satellite as the same force that pulls us down in everyday life is valid.

Yet you seem unhappy with it - so there must be more to the meaning of 'explanation', no?

#### 4throck

##### Enthusiast !
This reminded me of Feynman's answer on magnets in a BBC interview...

#### Ravenous

##### Donator
Donator
Actually - what would you accept as a valid answer to how something works if it's not math?

(genuinely curious - I think this is a difficult question, I have some ideas of my own, but I'd rather hear yours first).

I'd say biological evolution (by natural selection) - because although it's basically mathematics at its core (well maybe statistics), it's so intuitive in the way it works I think it becomes cumbersome to try and express it mathematically.

(This may not be a good answer though - after all people have been doing genetic programming in AI, etc. for years. They probably do have a reasonably tidy description.)

#### Shifty

##### Donator
Donator
I'd say biological evolution (by natural selection) - because although it's basically mathematics at its core (well maybe statistics), it's so intuitive in the way it works I think it becomes cumbersome to try and express it mathematically.

Evolution requires population genetics to have any rigor. And population genetics is statistics from top to bottom. It's true that you can explain evolutionary theory (of which natural selection is a part) in simple elegant language, but to be able to make predictions based on it, verify its accuracy and refine its formulation requires the rigor of mathematics, particularly when you add molecular genetics to the mix.

#### Andy44

##### owner: Oil Creek Astronautix
Let me play devils advocate here:

Fuel and air are mixed inside a cylinder and ignited, creating hot gasses which expand

But how does this actually work? Why does stuff ignite, why does ignition make anything hot (and what is heat in the first place?), and moreover, why do hot gases really expand?

So what you mean by giving an explanation here is providing a link to things we experience in daily life and hence do not question any more. We've all seen flames, so we don't really wonder how they really work. To us, the idea that hot gases expand is sort of obvious (though it wasn't through most of classic history). We know expanding stuff can push things.

In that sense, you can also explain gravity - it's the pull we feel, standing on Earth (and some of us might even have felt the lack of it during short free-fall periods). We all know what it is just as we know what a flame is or what heat is - unless we ask the question what it really is.

So I think if you take 'explanation' in the sense of 'link to stuff we know from experience', then explaining gravity affecting a satellite as the same force that pulls us down in everyday life is valid.

Yet you seem unhappy with it - so there must be more to the meaning of 'explanation', no?

You're making my point for me.

#### Thorsten

##### Active member
You're making my point for me.

Well, actually I'd like to know what that 'more' is in your case.

(I posed the same question yesterday to a good friend of mine, and her reply was straightforward in the sense that it only touched calculability and predictability, i.e. the math - she wasn't at all interested in any 'really' beyond that and willing to accept a concise formulation in equations as explanation - the point of this being - we're not all the same. We don't all mean the same thing when we ask for 'how it really works' - hence the question 'What would you accept as explanation?' is rather meaningful and not just a cheap trick).

#### Jeorbit

##### Donator
Donator
I just came across this article in French from Swiss research university EPFL about mass and gravity : https://qi.epfl.ch/question/show/314

I'm not sure how well Google Translate would do with it, but here are some interesting bits I found:

- They write about how Einstein predicted the existence of gravitational waves and their speed in 1916
- Then how we got the first proof of their existence much later, in 1974 when astronomers at Arecibo observed a binary pulsar, and found the orbital period of the two bodies were exactly as predicted by Einstein's GR. But at this stage and for the next 40 years, it was only an indirect observation.
- And then at last in September 2015 how LIGO observed spacetime distortion caused by two colliding blackholes. Several other observations were made in December 2015 and the last in January 2017.

This might not answer the "why" question, but nevertheless I feel that actually observing the warping caused by gravitational waves is a pretty big deal. Or not?

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#### Linguofreak

##### Well-known member
This might not answer the "why" question, but nevertheless I feel that actually observing the warping caused by gravitational waves is a pretty big deal. Or not?

Yes it is, and not least just as a feast of engineering. Now, the basic concept of a gravitational wave detector is simple enough: you just need an ear or a microphone. If you were close enough to a black hole merger, you would actually be able to hear it without special equipment. The impressive part is building a microphone sensitive enough to pick up gravitational waves from across the universe.

#### Col_Klonk

##### Member
If you live in a 1-dimensional world, all other larger dimensions will appear as a line in your world.

If you live in a 2-dimensional world, all other dimensions will appear at least a line, or a plane in your world.

If you live in a 3-dimensional world, all other dimensions will appear at least a line, plane, or a sphere in your world....

So gravity is pervasive and seemingly independent of dimensions.. may we go 4th dimension+ as we know it.

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#### statickid

##### CatDog from Deimos
Donator
Here's something to think about:

The usual takeaway from Flatland has something to do with n-dimensional beings having a better understanding of lower dimensions than its residents but also a type of unaware blindness of higher dimensions. Along with this idea people usually consider lower dimensions as accessible to higher dimensional beings. However, I feel the real situation is that while any given n-dimensional being can more easily imagine lower dimensions, they remain experientially out of reach. Moreover, in the physical realm, we can simulate 2-D realms easily, however we cannot actually create true 2-D or 1-D objects with our 3-D matter.

#### Thorsten

##### Active member
However, I feel the real situation is that while any given n-dimensional being can more easily imagine lower dimensions, they remain experientially out of reach. Moreover, in the physical realm, we can simulate 2-D realms easily, however we cannot actually create true 2-D or 1-D objects with our 3-D matter.

I'm not sure I understand the point here.

In what sense do lower dimensions remain 'out of reach' experimentally? It's quite possible to create model systems in which objects (particles, excitations,...) can just move in two dimensions and have no freedom in the third - and these agree very well with 2-dim theoretical models (as in fact they should).

And, if you believe Lisa Randall (or any random string theorist) our matter isn't actually 3d, it just appears so for all practical purposes.

Point being, the question what something actually is is a bit pointless, the question what it is for all practical purposes usually leads you somewhere.

#### statickid

##### CatDog from Deimos
Donator
I'm not sure I understand the point here.

In what sense do lower dimensions remain 'out of reach' experimentally? It's quite possible to create model systems in which objects (particles, excitations,...) can just move in two dimensions and have no freedom in the third - and these agree very well with 2-dim theoretical models (as in fact they should).

...

not "experimentally"

they are experientially out of reach, in that we can't actually transfer our experience (consciousness) into a 2-D plane, or even craft 2-D or 1-D objects, these objects remain conceptual in nature, limited to numerical modelling and calculation.

#### Thorsten

##### Active member
Oops - now that's a funny mis-reading :lol:

You're absolutely right of course, sorry - then it all makes sense.

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