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What are the particulars of gravity?

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An abstraction is precisely the collection of its particulars. That is, "red" is precisely the collection of all red things. The concept is formed by looking at objects and saying "that is red" (pointing to a fire-truck), "this thing is not red" (pointing to the grass), and so on. If a concept has no referents in reality, then it is a floating abstraction.

But what about gravity? The problem with gravity is that

1) Every object is affected by gravity in precisely the same way.

and

2) Even objects which do not fall downwards are nonetheless said to be affected by gravity.

To illustrate the problem, let's say that I say that I have discovered an entirely new thing, and I call it "nuyp". When you ask me to define "nuyp", I point to a random object in the room and say, "That is nuyp." And we go on like this for a long time until you finally give up on trying to understand what "nuyp" even is. You then tell me, "This isn't working. Just tell me, in plain English, what a 'nuyp' is." And then I respond, "A 'nuyp' is a blue sphere." You then hold up a blue ball and ask, "So this is a nuyp?", I respond, "Yes, that's a nuyp." You then hold up a coffee mug and ask, "But then, this is not a nuyp?" And finally, I say, "No, that's also a nuyp."

Is gravity, like nuyps, a floating abstraction?

(Heh, get it? Gravity... floating? Heh... I'll stop now...)

Edited by SpookyKitty

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18 minutes ago, SpookyKitty said:

Maybe the math checks out, but unless gravity has particulars, the philosophy is garbage.

You would be inverting the the relationship of philosophy to the special sciences with such an assertion, IMHO.

If you're interested in reducing the concept of gravity to the perceptual level, you need to identify the particulars the math relates to,  in order to determine if the math checks out or not.

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Newton said:  Hypotheses non fingo

I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called a hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction.

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1 minute ago, dream_weaver said:

You would be inverting the the relationship of philosophy to the special sciences with such an assertion, IMHO.

Absolutely not. No result of a special science can invalidate a philosophical concept. If a special science employs a concept that has no referents, then the special science is in philosophical error. That a special science committs a philosophical error is not itself an empirical claim which a special science can contradict.

Quote

If you're interested in reducing the concept of gravity to the perceptual level, you need to identify the particulars the math relates to,  in order to determine if the math checks out or not.

But there are no particulars that the math relates to. When we say that 2 + 2 = 4 because a collection of 2 rocks combined with another collection of 2 rocks results in a collection of 4 rocks, then what does it mean to say that 2 nuyps plus 2 nuyps is 4 nuyps?

Even if you were to reduce the concept of force to perceptual particulars, that would not help the situation, because, at the end of the day, gravity is defined as nothing more than a force, but the question remains, a force of what?

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3 minutes ago, New Buddha said:

Newton said:  Hypotheses non fingo

I have not as yet been able to discover the reason for these properties of gravity from phenomena, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called a hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this philosophy particular propositions are inferred from the phenomena, and afterwards rendered general by induction.

Newton admits that gravity has no particulars. So?

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An abstraction isn't a collection of particulars as much as it is going to refer to all instances of an existent that have existed and will ever exist. There is no "red particular"; there are particulars which have the characteristic "red".

Forming the concept is not simply labeling something as red and you suddenly have a valid concept. For concrete things, you would notice some perceptual distinction between two or more objects. That could be simple as "the color of the fire truck" and "the color of the grass". Not that you would see in those terms, you wouldn't need words to notice that. You could distinguish firetruck and grass that way. And from there you could eventually go on to omit all measurements of the firetruck except its red color. You then create a symbol for that abstraction, which is the word "red". What you would then have is the abstraction "red". But you are right to say that a floating abstraction has no referent in reality. If you skipped comparing two or more actual things, then you would get a floating abstraction.

Of course, it gets more complicated when you have abstractions from abstractions, which would include gravity. Even if all things are affected by gravity in the same way, that isn't to say it isn't distinguishing anything. You could distinguish types of motion, which would include momentum or centripetal force. Not only that, you would know that you could form the concept by observing actual things where you know other concepts derive (like motion). In other words, you should be able to follow your concepts down until you get to an object. Something concrete.

A "nuyp" might not technically be a floating abstraction. The problem with that one is that it seems to multiply concepts beyond necessity because there is no apparent cognitive role for the concept. This would make the concept invalid. Then again, your example might not be complete. It might just mean the learner is having a difficult time. Pointing can and does work, but only if there is something to actually distinguish. With gravity, you can actually distinguish (if you are trying to check that the concept reduces to reality) between "oh, that ball keeps going because of momentum" and "the apple fell because of gravity".

EDIT: I understand that gravity is just a force, it would still need to connect to reality in some way. Gravity itself might not be a concrete thing, but its existence depends on some relation between two or more objects (or however specifically the phenomenon is described). So, it can still be reduced to something concrete, but it would be very complicated and take many steps.

Edited by Eiuol

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7 minutes ago, SpookyKitty said:

Absolutely not. No result of a special science can invalidate a philosophical concept. If a special science employs a concept that has no referents, then the special science is in philosophical error. That a special science committs a philosophical error is not itself an empirical claim which a special science can contradict.

If you hold to this, then the question you raised should dissolve itself.

9 minutes ago, SpookyKitty said:

But there are no particulars that the math relates to. When we say that 2 + 2 = 4 because a collection of 2 rocks combined with another collection of 2 rocks results in a collection of 4 rocks, then what does it mean to say that 2 nuyps plus 2 nuyps is 4 nuyps?

Math is derived from particulars as well. Quite another reduction than that of gravity, but still reducible, as I understand Dr. Corvini .

12 minutes ago, SpookyKitty said:

Even if you were to reduce the concept of force to perceptual particulars, that would not help the situation, because, at the end of the day, gravity is defined as nothing more than a force, but the question remains, a force of what?

Your point being . . . ?

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12 hours ago, SpookyKitty said:

An abstraction is precisely the collection of its particulars [...]

But what about gravity? The problem with gravity is that

1) Every object is affected by gravity in precisely the same way.

and

2) Even objects which do not fall downwards are nonetheless said to be affected by gravity.

I am trying to understand your description of the problem. Let's see if I got it right.

Your first starting point is that all object are "affected by gravity in precisely the same way". You then infer that there are no really different instances of the gravitational action, so that there is apparently not possible to form a concept – "gravity" - that encompasses all these different instances.

Does this correctly describe your problem? If not, please restate your problem.

Do you see this problem as being proper to gravitation only, or also to other types of interactions? I am aware that this might depend on what do you exactly mean by "affected by gravity in precisely the same way". Please explain.

(I am not yet sure what role does your second starting point have…)

Edited by AlexL

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11 hours ago, SpookyKitty said:

An abstraction is precisely the collection of its particulars.

I'm gonna stop you right there. It's not. An abstraction is a mental construct, not a collection of anything. A collection of concretes would still be a concrete. An abstraction is the exact opposite of a concrete.

Quote

That is, "red" is precisely the collection of all red things.

You really don't see why that's an absurd thing to say?

Edited by Nicky

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SK, aren't you simply trying to discuss the ontology of forces? 

Your question about gravity is essentially asking, "what do I differentiate gravity from to form the concept if it is universal", right? 

Edit:

SK said:

Quote

An abstraction is precisely the collection of its particulars.

No, the meaning of an abstraction is its units, past, present and future. Abstraction qua abstraction is a cognitive process.

http://aynrandlexicon.com/lexicon/unit.html

http://aynrandlexicon.com/lexicon/meaning_(of_concepts).html

Edit:

SK said:

Quote

Absolutely not. No result of a special science can invalidate a philosophical concept. If a special science employs a concept that has no referents, then the special science is in philosophical error. That a special science committs a philosophical error is not itself an empirical claim which a special science can contradict.

This is all correct. Now, does this mean that you are claiming that the theoretical concept gravity is philosophically vetoed by an epistemic or metaphysical violation? It sounds like you are....? 

Another edit:

I guess your question in the OP about "floating abstraction" answers the above.

Edited by Plasmatic

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10 hours ago, SpookyKitty said:

Even if you were to reduce the concept of force to perceptual particulars, that would not help the situation, because, at the end of the day, gravity is defined as nothing more than a force, but the question remains, a force of what?

Modern science doesn't consider gravity a force. There are many theories on what gravity is, but the simplest one that is consistent with experimental data is Einstein's General Relativity.

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2 hours ago, Nicky said:

Modern science doesn't consider gravity a force... but the simplest one that is consistent with experimental data is Einstein's General Relativity.

In fact the simplest is Newton's theory (where gravity is a force), and I gusss it is sufficient for the current subject - if I correctly understood it... 

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40 minutes ago, AlexL said:

In fact the simplest is Newton's theory (where gravity is a force), and I gusss it is sufficient for the current subject - if I correctly understood it... 

Yes, but Newton's theory isn't consistent with all experimental data (and even in contexts where it is, it is more of an observation about the effects of gravity than an explanation of what gravity IS).

Einstein's theory is the simplest that still holds true when we look at the world carefully.

As for the current subject, OP dialing down the mindless arrogance, and paying a little attention to people with the ability to use logic and meaningful language, is all that would be needed to settle it.

Edited by Nicky

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3 minutes ago, Nicky said:

Newton's theory isn't consistent with experimental data. Einstein's theory is the simplest that does THAT.

You missed my caveat "it is sufficient for the current subject - if I correctly understood it...".

Newton's theory is consistent with data to a very high precision, except for quite exotic circumstances. But it is up to SK to specify if the Newton's view of gravitation is sufficient for her purpose.

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21 minutes ago, AlexL said:

You missed my caveat "it is sufficient for the current subject - if I correctly understood it...".

Newton's theory is consistent with data to a very high precision, except for quite exotic circumstances. But it is up to SK to specify if the Newton's view of gravitation is sufficient for her purpose.

OP is asking about what gravity is. So what is it? Is it a force or is it not a force? As per the Law of Identity, it can't be both, you have to pick one or the other. I pick the latter, because the latter is consistent with a theory that has ALWAYS been confirmed by empirical evidence. Even in "exotic circumstances".

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Newton's theory is sufficient for our purposes here (the situation is unchanged in General Relativity in any case and it will only complicate matters without necessity). Also, by "gravity affecting every object in the same way", I mean that the law of gravity applies to every physical situation.

My argument restated is as follows. Since the identification of a concept requires situations in which it does and does not obtain (even if these situations are entirely abstract), and since gravity obtains in every situation, it shouldn't be possible to have a concept of gravity that isn't just a floating abstraction.

But gravity is a useful and non-vacuous concept. So either,

a) gravity is, in fact, a floating concept, and Newton's theory is mistaken in some sense, or

b ) gravity does have particulars, or

c) we can have valid concepts which are not derived from distinctions among entities.

I don't think anyone will seriously defend a), that most people are defending b ), whereas, in my opinion, c) is the best option.

In defense of b ), some have argued that since gravity is a concept based on mathematics, and since mathematics is reducible to distinctions in concrete situations, gravity has particulars. But mathematical concepts merely describe real phenomena, they are not the phenomena themselves. To see the difference more clearly, most forces are the result of some object acting on another object. For example, when a person pushes on a block, that exerts a force on the block, and if the person does not push on a block, the force, likewise, disappears. Thus, mechanical forces of this type would constitute a valid concept, and the mathematical notion of force merely describes the real situation in which there is a real force. In other words, in order for the mathematical concept of force to describe a real situation it must be a force of something which is actually real. Gravity, by contrast seems to be caused by nothing at all, obtains in every situation, and is defined as nothing other than a force.

Eiuol also defends b ) and argues that gravity distinguishes among types of motion. In other words, he argues that we are able to look at a type of motion and decide whether or not it is caused by gravity or something else. But this is not true. If we only ever observe the trajectory of an object, the most we can derive from that is its velocity and acceleration functions. If we also knew its mass, we would be able to calculate the net force on the object at every point along its trajectory. But we could go no further, as the net force is a sum of all forces on the object no matter what they are, and once they've been summed together, it's impossible to know what the original forces were.

I have said earlier that c) is the best option. The concept of gravity is not derived from distinctions among concrete situations nor from distinctions among abstract concepts which are themselves derived from distinctions among concrete situations and so on. Instead, I think that the concept arises from a "copy and paste" of the concept of force from "normal" situations (where it is clear that the force is caused by some object acting on another and where the corresponding force disappears if the action of the object does) to every possible situation, even ones where no forces (besides gravity) apply.

 

 

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Its instructive to note how the skepticism of both ostensive definition and a reduction of a concept that applies to all contexts, is being reiterated here just as it was laid out in the "foundation of physics" thread. 

The concept of gravity was a rhetorical device, a foil for the rejection of the reduction of fundamental concepts to perception.

"Either reject gravity or reject your epistemology" is a rank hierarchy inversion.

 

Edit:

SK said:

Quote

Gravity, by contrast seems to be caused by nothing at all, ....

This is not true anyway. Look up the relationship of mass to GR for the Consensus view of gravitation.

Edited by Plasmatic

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1 hour ago, Plasmatic said:

Its instructive to note how the skepticism of both ostensive definition and a reduction of a concept that applies to all contexts, is being reiterated here just as it was laid out in the "foundation of physics" thread. 

The concept of gravity was a rhetorical device, a foil for the rejection of the reduction of fundamental concepts to perception.

"Either reject gravity or reject your epistemology" is a rank hierarchy inversion.

Does gravity reduce to perception or doesn't it? If it does, then what does it reduce to? And if not, then why is it a valid concept?

There is no "foil" or a "rejection" of anything. When something can be questioned, I question it. Your calling this geniuine epistemological problem a "heirarchy inversion" is just a cop-out to avoid having to think.

Quote

This is not true anyway. Look up the relationship of mass to GR for the Consensus view of gravitation.

No, mass does not "cause" gravitation. A cause is a relationship between events in spacetime, according to GR. Neither Stress-energy (which includes mass) nor spactime curvature are "events", so it doesn't make any sense to say that one causes the other. They are related, but the relationship is not causal. Rather, the relationship between them is that of a physical law.

Edited by SpookyKitty

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2 hours ago, SpookyKitty said:

Eiuol also defends b ) and argues that gravity distinguishes among types of motion. In other words, he argues that we are able to look at a type of motion and decide whether or not it is caused by gravity or something else. But this is not true. If we only ever observe the trajectory of an object, the most we can derive from that is its velocity and acceleration functions. If we also knew its mass, we would be able to calculate the net force on the object at every point along its trajectory. But we could go no further, as the net force is a sum of all forces on the object no matter what they are, and once they've been summed together, it's impossible to know what the original forces were.

It's more like a mix of B ) and C). That is, there are particulars to observe which exhibit an identity, and from those identities phenomena can Be identified which aren't necessarily an aspect of strictly the particulars. A concept of gravity is abstract enough that no thing on its own exhibits gravity. It is built up one abstraction at a time so that gravity is really coming from elaborations and abstractions about forces and motion. I probably used a bad example to say momentum is for example distinguished from gravity. It maybe can't be, but gravity is a distinction among other abstractions. What do those abstractions underneath refer to? And so on. If the "and so on" ends with an entity, it is not a floating abstraction.

A really rough idea:

gravity

forces

motion

entity

Gravity rests on distinctions of forces. Forces rest on motion. Motion rests on entities. The point here is that prior distinctions allow for realizing an abstraction. That's the form of how valid concepts rest on other concepts. Even from what you described so far, I don't see the concept of gravity as incompatible. It seems when you ask about reduction, you were thinking of reduced to perception is straight from gravity to entity. You would be right, gravity can't be reduced in -that- way, nor does it need to in order to be valid. (Reduction like that would be an empiricist error: that if you can't directly go from abstraction to concrete, it must not be valid or "real").

Edited by Eiuol

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2 hours ago, SpookyKitty said:

There is no "foil" or a "rejection" of anything. When something can be questioned, I question it.

Questioning is good, when your questions are valid ones! Your questions are indeed the result of your current skepticism-rejection of the very things I mentioned.

Your comment:

Quote

To illustrate the problem, let's say that I say that I have discovered an entirely new thing, and I call it "nuyp". When you ask me to define "nuyp", I point to a random object in the room and say, "That is nuyp." And we go on like this for a long time until you finally give up on trying to understand what "nuyp" even is. You then tell me, "This isn't working. Just tell me, in plain English, what a 'nuyp' is."

Is indeed a reiteration of your earlier claim that ostensive definitions are not sufficient for defining metaphysical concepts because they don't reduce to perception

Those two, skepticism and questioning are not mutually exclusive.

I don't think you know what I meant by a hierarchy inversion. You have to use the science of epistemology to discover any fact. You don't use a discovery of special science to question epistemology for that reason. The question you are asking doesn't even depend on the theoretical conception in GR, or of gravity to be asked.  The question "are there concepts that are valid but do not reduce to a base in perceptual entities" does not depend on any special science knowledge whatever and there is no special privilege granted to any special science concepts that exclude it from philosophical scrutiny.

Edit:   "Does gravity reduce to perception"?

a special science concept, particularly one involving theoretical objects could fail to be a valid concept and still not answer the philosophical question "are there concepts that are valid but do not reduce to a base in perceptual entities".

2 hours ago, SpookyKitty said:

Your calling this geniuine epistemological problem a "heirarchy inversion" is just a cop-out to avoid having to think.

On the contrary, I have done quite a lot of thinking on the Philosophy of Science and Physics. It's one of my favorite subjects. Enough thinking to know that neither "events", nor "space", nor "time" constitute special science concepts and that none of them qualify as "causes"... Whatever the particulars that possess mass interact with, it isn't any of those three.

 

2 hours ago, SpookyKitty said:

No, mass does not "cause" gravitation. A cause is a relationship between events in spacetime, according to GR. Neither Stress-energy (which includes mass) nor spactime curvature are "events", so it doesn't make any sense to say that one causes the other. They are related, but the relationship is not causal. Rather, the relationship between them is that of a physical law.

See above. I only mentioned mass because I don't recognize the rest as qualifying as causal agents. (Even here there is a question for me because the Ricci tensor is 0)

Edited by Plasmatic

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4 hours ago, SpookyKitty said:

Since the identification of a concept requires situations in which it does and does not obtain (even if these situations are entirely abstract), and since gravity obtains in every situation, it shouldn't be possible to have a concept of gravity that isn't just a floating abstraction.

Concept:

Quote

A. Rand: A concept is a mental integration of two or more units which are isolated by a process of abstraction and united by a specific definition. 

AR: A concept is a mental integration of two or more units possessing the same distinguishing characteristic(s), with their particular measurements omitted.

I'll stay in the realm of the classical (Newtonian) theory of gravitation, as you specified. I therefore think that GR is off-topic in this thread.

Physicists have established that any two object possessing mass interact, that is influence each other's movement. From this discovery steams the concept of gravitation and gravitational interaction. The identification of this phenomenon does not require the existence of situations where such an interaction does not exist.

The gravitation does have "particulars". The "particulars" of gravitation are interactions of any pair of objects possessing different masses (or mass distributions) and/or situated at different relative positions. (The dependence of the gravitational interaction on only these two characteristics is established by observation.)

Physicist have introduced concepts and tool to characterize quantitatively this (and other kind of) interactions. The gravitational interactions are characterized quantitatively by essentially the same concepts and tools as other kinds of interactions, be they of the action-at-a-distance kind or contact interactions. You singled out the latter type (a person pushes a block, etc.) and labeled it as somehow more "real", while in fact there is no reason to do this.

The tools physicists have introduced in order to characterize interactions of any kind are forces – described by vectors and tensors; it is understood that we are talking here of macroscopic, non-relativistic and non-cosmological realm (I am being super-cautious ;)). Correspondingly, both contact and longer range interactions, including the gravitational one, are described in a unified manner. In all this cases "the force is caused by some object acting on another" and would not exist in the absence of that object. In the case of longer-range forces, they would decrease with the distance between the objects, but not always totally disappear. 

Gravity is in some ways similar to the electrostatic force; I am not sure if you see the same conceptual difficulties also for the latter. Gravitation has some unique characteristics, but I will not go into this now because, as I said, I don't know if this is relevant for you - for your subject, that is.

PS: Gravitation is perceptually detectable

PPS: Gravitation is caused by the mass characteristic of the objects. This is demonstrated by the fact that the less massive an object is, the less intense does it gravitationally interact with other objects.

PPPS ;) : In GR gravity is caused by object's mass, but not directly as in the classical theory, but indirectly, by curving the space-time at the place where the second object exists.

Edited by AlexL

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1 hour ago, Eiuol said:

It's more like a mix of B ) and C). That is, there are particulars to observe which exhibit an identity, and from those identities phenomena can Be identified which aren't necessarily an aspect of strictly the particulars. A concept of gravity is abstract enough that no thing on its own exhibits gravity. It is built up one abstraction at a time so that gravity is really coming from elaborations and abstractions about forces and motion. I probably used a bad example to say momentum is for example distinguished from gravity. It maybe can't be, but gravity is a distinction among other abstractions. What do those abstractions underneath refer to? And so on. If the "and so on" ends with an entity, it is not a floating abstraction.

A really rough idea:

gravity

forces

motion

entity

Gravity rests on distinctions of forces. Forces rest on motion. Motion rests on entities. The point here is that prior distinctions allow for realizing an abstraction. That's the form of how valid concepts rest on other concepts. Even from what you described so far, I don't see the concept of gravity as incompatible. It seems when you ask about reduction, you were thinking of reduced to perception is straight from gravity to entity. You would be right, gravity can't be reduced in -that- way, nor does it need to in order to be valid. (Reduction like that would be an empiricist error: that if you can't directly go from abstraction to concrete, it must not be valid or "real").

That is not necessary. A reduction of gravity to something that itself can be reduced to the perceptual level would be acceptable.

In this case, no, gravity is not reducible to distinctions among forces either. Forces have a direction and a magnitude, but there is no particular combination of direction and magnitude which correspond to gravity. The force of gravity may have any direction or magnitude.

39 minutes ago, Plasmatic said:

Questioning is good, when your questions are valid ones! Your questions are indeed the result of your current skepticism-rejection of the very things I mentioned.

Your comment:

Is indeed a reiteration of your earlier claim that ostensive definitions are not sufficient for defining metaphysical concepts because they don't reduce to perception

Those two, skepticism and questioning are not mutually exclusive.

So if you don't believe something, it is invalid to question it or consider its existence?

But no, the two things are not the same, because gravity is not a metaphysical concept but a physical one.

And my questioning is not the result of any skepticism, my skepticism is the result of the fact that the case of gravity poses a challenge to the standard Objectivist account of concept formation

Quote

I don't think you know what I meant by a hierarchy inversion. You have to use the science of epistemology to discover any fact. You don't use a discovery of special science to question epistemology for that reason. The question you are asking doesn't even depend on the theoretical conception in GR, or of gravity to be asked.  The question "are there concepts that are valid but do not reduce to a base in perceptual entities" does not depend on any special science knowledge whatever and there is no special privilege granted to any special science concepts that exclude it from philosophical scrutiny.

You have misunderstood the nature of the question. If epistemology claims that all valid concepts arise from distinctions among entities (concrete or abstract) and if you have a valid concept (in this case, gravity) which does not arise in that way, then there is a problem. Either the account is false and must be modified, or gravity is an invalid concept. (Or gravity is a valid concept consistent with the standard account of concept formation, in which case it must be proven that it is).

Your claim that this is not the case is a denial of simple logic.

Hierarchy inversion is when epistemology is used to prove or disprove an empirical claim or vice versa. But gravity is not an empirical claim. It is a concept that is used to explain emirical facts, and its validity is open to philosophical scrutiny.

Quote

Edit:   "Does gravity reduce to perception"?

a special science concept, particularly one involving theoretical objects could fail to be a valid concept and still not answer the philosophical question "are there concepts that are valid but do not reduce to a base in perceptual entities".

Yes, exactly. A scientific concept can fail to be valid, in which case it would not contradict the epistemological claim. If gravity is an invalid concept, then there is no problem.

Quote

On the contrary, I have done quite a lot of thinking on the Philosophy of Science and Physics. It's one of my favorite subjects. Enough thinking to know that neither "events", nor "space", nor "time" constitute special science concepts and that none of them qualify as "causes"... Whatever the particulars that possess mass interact with, it isn't any of those three.

Well General Relativity considers them as such, so tough luck.

Oh and mass-energy actually curves spacetime, so there's that.

Quote

See above. I only mentioned mass because I don't recognize the rest as qualifying as causal agents. (Even here there is a question for me because the Ricci tensor is 0)

What?

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2 hours ago, SpookyKitty said:

That is not necessary. A reduction of gravity to something that itself can be reduced to the perceptual level would be acceptable.

Which part isn't necessary? I am only trying to show that it didn't seem like you understood the Objectivist position of the way a concept is reduced to perception. It doesn't mean finding the particular (if by particular you mean a concrete object) of the concept unless it is first-level (as in things like apple, firetruck, dog, etc). We aren't looking for a "gravity particle" necessarily for example.

By the way, I'm not claiming that -that- reduction is correct necessarily, only that a reduction would be -like- that. It'd take that form. As I said, it's a rough idea. To do it right, it'd take a lot more work and require a lot more concepts. AlexL would probably know better than me all the concepts required. I don't think anything you said means gravity can't be reduced to perception. All you really said is "gravity is really complicated, a proper reduction is tough!"

 

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