Gravity: What We Know vs What We Don't

[Seph83]

I think the simplist answer is we know NOTHING about gravity.

there is only theory on what gravity actually is... all we know are its effects.

for example the mayans knew with amlost perfect accuracy about the suns behavior to such a degree that they could predict the Earth's presession. Buut they had absolutly no knowledge of anything ABOUT the sun, like nuclear fusion and photons.

That is pretty much where we are at the moment. We understand gravity's behavior with an extraordinary degree of accuracy, however we know absolutly nothing about gravity.

 

[russ_watters]

We understand gravity's behavior with an extraordinary degree of accuracy, however we know absolutly nothing about gravity.

Those two statements contradict each other. Being able to make accurate predictions is all that we ask of science.

 

[Seph83]

If that is all you want to know then I am envious.

 

[ZapperZ]

I think the simplist answer is we know NOTHING about gravity.

there is only theory on what gravity actually is... all we know are its effects.

for example the mayans knew with amlost perfect accuracy about the suns behavior to such a degree that they could predict the Earth's presession. Buut they had absolutly no knowledge of anything ABOUT the sun, like nuclear fusion and photons.

That is pretty much where we are at the moment. We understand gravity's behavior with an extraordinary degree of accuracy, however we know absolutly nothing about gravity.

This is misleading. If you look carefully at everything that you think you know, you will see that all you know is actually just your ability to describe something. The knowledge of a set of properties and behavior of something is what constitutes your ability to say that you know what it is. Now it doesn't mean that you know EVERYTHING about it, but it certainly does not allow you to say you know NOTHING about it.

Physics is just that - our ability to describe the behavior of a system. There's no greater evidence to show that we know quite a bit about something when we can make quantitative prediction of what that something is going to do. Look at your modern electronics. I will even say that we know more about gravity than you know more about the behavior of your closest relatives.

Zz.

 

[Defennder]

The problem is, you can always keep asking "Why?" for any explanation offered. Unless you believe that the fundamental facts of our universe are somehow reducible to axioms of logic.

 

[Seph83]

I will even say that we know more about gravity than you know more about the behavior of your closest relatives.

Zz.

lol... that wouldn't surprise me. I don't claim to be able to predict the behavior of my closest relatives... AT ALL

I don't want to start an argument. I am just trying to put across that saying all you want to know is the behavior of a "thing" is like saying all you want to know is how to drive a car but not caring how a car operates.

Of course "why" will be the eternal question to every answer and I hope we will never stop asking.

 

[ZapperZ]

lol... that wouldn't surprise me. I don't claim to be able to predict the behavior of my closest relatives... AT ALL

I don't want to start an argument. I am just trying to put across that saying all you want to know is the behavior of a "thing" is like saying all you want to know is how to drive a car but not caring how a car operates.

Of course "why" will be the eternal question to every answer and I hope we will never stop asking.

Then don't claim that we know nothing about it. The pedestrian definition of "knowing nothing" simply does not apply here. Would you depend your life on something that we know nothing about? Honestly?

You haven't shown an example where it fits into your criteria of knowing "something". If that doesn't exist, then your categorization that we know nothing about gravity is moot.

Zz.

 

[Seph83]

To know something we would know the cause of gravity. We would also have a model that would work universally from macro to plank space. Perhaps a theory exists that I don't know of, but even then it will just be a theory.

 

[ZapperZ]

To know something we would know the cause of gravity. We would also have a model that would work universally from macro to plank space. Perhaps a theory exists that I don't know of, but even then it will just be a theory.

But see, when you find the "cause" of something, that "explanation" really is a description at that lower level.

You haven't managed to find an example in physics where you can say that there is this "cause". What about E&M? Or the strong force, etc... etc.? By your criteria, do you also claim that we know nothing about physics, and thus, we know nothing about everything in our universe?

Zz.

 

[Seph83]

Your not far off

I'm bound to get shot for saying this on a physics forum but to quote socrates "True knowledge exists in knowing that you know nothing."

See what you made me do! This is a thread about gravity and you have reduced me to a level where philosophy has had to enter discussion!

I warned you I didn't want to start an argument.

 

[ZapperZ]

Your not far off

I'm bound to get shot for saying this on a physics forum but to quote socrates "True knowledge exists in knowing that you know nothing."

See what you made me do! This is a thread about gravity and you have reduced me to a level where philosophy has had to enter discussion!

I warned you I didn't want to start an argument.

Then you have a strange of not wanting to start an "argument" by knowingly starting something that you KNOW will get a reaction. And since when do you go by your understanding our your world based on some "quotation"?

So you still haven't been able to show me an example of something that you know. Then I will resort to having ask you this: What is an apple?

Or are you also claiming that you know nothing about an apple?

Zz.

 

[Seph83]

ok... I am going to have to stop this now.

Yes I can tell you what an apple is. and, like gravity, I can tell you how it behaves. If you want to know then pm me because you are taking this thread way off topic.

 

[ZapperZ]

This is no longer off-topic. So tell me, what is an apple that you think you know?

Zz.

 

[LightbulbSun]

The thread title is contradictory. I'll give you a hint, it's within the part that says "know nothing."

 

[ZapperZ]

It's a title that I came up on the fly since these posts were split from another thread. It is consistent with the first post.

Zz.

 

[rewebster]

If I can assume what Seph83 may be saying, is that, he would like to know a little more of what's going on in the way gravity works---more of the 'reasons' how/why gravity works.

Two hundred years ago to now, more knowledge has been gained as to the make up and the nature of things, but still there is no explanation written in any books as to the fundamental and foundational aspects of gravity. We know more about an apple in a lot of ways for 'what' an apple is, as to the same thinking as what is common knowledge/written about gravity (and a few more of those type of things).

 

[Crosson]

So tell me, what is an apple that you think you know?

Apples can be http://en.wikipedia.org/wiki/Ostensive_definition" .

 

[Gear300]

I think the simplist answer is we know NOTHING about gravity.

there is only theory on what gravity actually is... all we know are its effects.

for example the mayans knew with amlost perfect accuracy about the suns behavior to such a degree that they could predict the Earth's presession. Buut they had absolutly no knowledge of anything ABOUT the sun, like nuclear fusion and photons.

That is pretty much where we are at the moment. We understand gravity's behavior with an extraordinary degree of accuracy, however we know absolutly nothing about gravity.

There was a PF member that said this...forgot the name, but to put it simply: science tells the how rather than the why.

 

[rewebster]

Apples can be http://en.wikipedia.org/wiki/Ostensive_definition" .

yep---there's a cop-out way physicists/scientists answer a lot of these 'questions' especially if someone asks something like, "why does gravity work the way it does?"

The aloof answer physicists/scientists give is: " 'Why...?' is a question for philosophers not for scientists-----scientists blah, blah, blah..."--especially if its something they don't know the 'real' answer to.

 

[Crosson]

The problem with asking "What is gravity?" is that this is a loaded question; it assumes that 'gravity' is the name of something. General Relativity shows us that this is a bad assumption. This is the same problem that comes from a question like 'What is time?', this assumes that 'time' is the name of something. A better question would be "Under what circumstances do we use the word 'time'?", since this explores the meaning of the concept without starting with a loaded question.

 

[Seph83]

Crosson, rewebster, and gear300 have put it very well.

I can tell you what an apple is. An apple is a fruit that grows on an apple tree that contains seeds that can grow into other apple trees. It is biological and consists of cells. They are usually red, have a waxy skin and are very tasty, except the skin gets stuck in my teeth. :D

 

[ZapperZ]

Crosson, rewebster, and gear300 have put it very well.

I can tell you what an apple is. An apple is a fruit that grows on an apple tree that contains seeds that can grow into other apple trees. It is biological and consists of cells. They are usually red, have a waxy skin and are very tasty, except the skin gets stuck in my teeth. :D

... and what you have done is give a list of description of an apple and all its associated properties. Have you managed to "explain" what an apple is?

Zz.

 

[Seph83]

I have explained what an apple is. An apple is a fruit that grows on an apple tree. I understand what you are saying but you are asking the wrong questions.

 

[ZapperZ]

I have explained what an apple is. An apple is a fruit that grows on an apple tree. I understand what you are saying but you are asking the wrong questions.

What is wrong about it?

"An apple is a fruit that grows on an apple tree" is the same as "gravitational force is the force of attraction between two bodies with mass".

In the end, both are "descriptions" of the property of the subject matter. If you claim that you know something about an apple, then how come you claim that "we" know nothing about gravity?

Zz.

 

[Seph83]

The key difference between these two expressions is the word Fruit and Force. Fruit can be defined but can you tell me what force is?

Saying it is a force is merely describing its behavior. Like saying an apple is tasty.

EDIT : and I just noticed you haven't described what gravity is as you have described what "Gravitational force" is

 

[rewebster]

What is wrong about it?

"An apple is a fruit that grows on an apple tree" is the same as "gravitational force is the force of attraction between two bodies with mass".

In the end, both are "descriptions" of the property of the subject matter. If you claim that you know something about an apple, then how come you claim that "we" know nothing about gravity?

Zz.

The 'apple' analogy may not be the best----as it is a 'physical' thing----I think I remember you using the apple analogy before. It seems you may be putting 'gravity' in the area as 'love', 'hate', or an 'argument'.

OK----let's do it this way----

Are you, personally, 'satisfied' with YOUR knowledge about an apple?

Are you, personally, 'satisfied' with YOUR knowledge about gravity?

 

[cristo]

I sense that this discussion is going to continue ad nauseam. I doubt that you will accept any answer, and will keep picking down to the level of asking for a definition of "between."

By the way, gravity and gravitational force, are the same thing.

Are you, personally, 'satisfied' with YOUR knowledge about gravity?

That's a completely different question: no physicist will answer yes to that!

 

[Seph83]

rewebster,

now those are good questions!

If you are satisfied with your knowledge then in your little world you are confident that you know what something is. If you are unsatisfied, then the opposite is true.

However I stand by my original statement but perhaps we can compromise.

how about this:

"All we know about gravity is its behavior."

 

[ZapperZ]

The key difference between these two expressions is the word Fruit and Force. Fruit can be defined but can you tell me what force is?

Saying it is a force is merely describing its behavior. Like saying an apple is tasty.

No, if you look carefully, the definition of a fruit is also a "description" (it has "seeds" as an example). So your "explanation" really isn't one if you look deeper into it. I can do the same with "force" as being the gradient of a potential energy field. And one can also do the same with that "definition", because we can continue asking "but what is a potential energy field"?

The point here being that every thing you perceive to be an "explanation", really isn't, because as you go to a lower level, it becomes a description.

Not only that, saying an "apple" is a "fruit" is no different than pointing to a periodic table, i.e. using a made-up categorization of the property of a set of objects. It explains nothing. It only appears as if you have made an explanation because you are living in an world in which the word "fruit" is a familiar idea. So when you say that, people seem to think they know what it is and it satisfies their question on what it is. However, trying telling that to an alien who knows nothing about the concept of a fruit. You'll end up describing what it is based on the description of what a fruit is supposed to be.

This is what physics has to do since it has to describe the physical world but not in terms of any cultural/social connotations. Another alien coming here on Earth will still measure the rate of fall of objects on the surface of the Earth with the SAME description that we have, whether they understood Newton's laws or not.

EDIT : and I just noticed you haven't described what gravity is as you have described what "Gravitational force" is

So what's the difference? We know nothing about gravity, but actually know something about gravitational force?

Zz.

 

[Seph83]

By the way, gravity and gravitational force, are the same thing.

I understand what you are saying, but in his definition of gravitational force he has used the word force to describe what it is.

That is similar to saying that the definition of Happiness is feeling happy. It defines itself and therefore requires no further explanation.