Can we know that something doesn't exist?

@hue-man,

Night Ripper wrote:

But it can be falsified, if we ever observe something traveling faster than light. That's not possible to do with "nothing ever has or ever will travel faster than the speed of light" vs. "nothing can travel faster than the speed of light". That's the difference.

Ok, then stick with "nothing can travel faster than the speed of light". Any more problems?

But keep in mind that physical impossibility is not saying "ever has or ever will", it is saying "can't" to mean nothing can (from our knowledge). That's my point. At least that's what I understand it to mean, based upon the ways I've seen people use the term. Do you have sources which state the contrary? If so, please provide them.

@Zetherin,

Zetherin;137548 wrote:

physically impossible means that which is in violation of the laws of physics

Another problem with this notion, even as a common usage definition, is that the laws of physics change. This means that before Newton, a lot of impossible things routinely happened.

@Zetherin,

Zetherin;137561 wrote:

At least that's what I understand it to mean, based upon the ways I've seen people use the term. Do you have sources which state the contrary? If so, please provide them.

It's called Regularity. Here's the article I posted earlier. That's the side I'm on. You seem to be on the side of Necessity.

Laws of Nature [Internet Encyclopedia of Philosophy]

---------- Post added 03-08-2010 at 01:27 PM ----------

ughaibu;137562 wrote:

Another problem with this notion, even as a common usage definition, is that the laws of physics change. This means that before Newton, a lot of impossible things routinely happened.

The laws of science change. The laws of nature don't change. It's either true or false that "nothing ever travels faster than the speed of light" but that truth value doesn't, can't, change.

Please do not confuse the laws of science and the laws of nature. The laws of science are only approximations of the literally true, laws of nature.

@Night Ripper,

Night Ripper;137563 wrote:

Please do not confuse the laws of science and the laws of nature. The laws of science are only approximations of the literally true, laws of nature.

I'm not familiar with this way of looking at it. What's an example of a law of science vs. a law of nature?

A person has a sense of knowing that events are ordered in some way.

This might be explained by pointing to a fundamental demand for meaning. Without order, there would be no meaning.

So if you note that your purpose in speaking is to say something meaningful, you're automatically bound to confidence that there is order. Otherwise you wouldn't be talking.

Now that we're bound to the idea of order, we could imagine a super-personality ordering events... as each of us orders his or her own micro-world. So we now notice the idea of will.

Or, we could imagine that events passively unfold in accord with a hidden pattern (like a .... clock?)

Have we yet founded any particular sense of knowing? Or have we just enjoyed exploring ten ways from Sunday how such a foundation might be... found? Cogito ergo sum. Then what?

@Night Ripper,

Night Ripper;137563 wrote:

Please do not confuse the laws of science and the laws of nature. The laws of science are only approximations of the literally true, laws of nature.

Of course. But the realists about physical possibility have specified laws of physics.

@hue-man,

Night Ripper wrote:

It's called Regularity. Here's the article I posted earlier. That's the side I'm on. You seem to be on the side of Necessity.

Laws of Nature [Internet Encyclopedia of Philosophy]

I think it is necessary that water is H2O, and I think it is necessary that water has specific properties which makes it water (essential properties), for instance. But it is hard for me to say that everything we call physically impossibly, I think is necessarily so. So, my gut tells me I'm on the fence.

"In contrast, when Regularists say that some situation is physically impossible - e.g. that there is a river of cola - they are claiming no more and no less than that there is no such river, past, present, future, here, or elsewhere. There is no nomic dimension to their claim. They are not making the modal claim that there could not be such a river; they are making simply the factual (nonmodal) claim that there timelessly is no such river. (Further reading: 'The' Modal Fallacy.)"

That is what I was expressing the entire time! I suppose my understanding of physical impossibility is a regularist one!

@Zetherin,

Zetherin;137571 wrote:

I think it is necessary that water is H2O, and I think it is necessary that water has specific properties which makes it water (essential properties)

I don't agree with Kripke on that but I'm not confident enough yet with my understanding of him to say exactly why he's wrong. So, I'll just hold my tongue for now.

Zetherin;137571 wrote:

That is what I was expressing the entire time! I suppose my understanding of physical impossibility is a regularist one!

Well we seem to be the minority then. Every argument against free will on these forums seems to assume necessity. (See: "The Regularists' Trump Card - The Dissolution of the Problem of Free Will and Determinism" in section 5f Laws of Nature [Internet Encyclopedia of Philosophy])

@Night Ripper,

Night Ripper;137576 wrote:

Well we seem to be the minority then. Every argument against free will on these forums seems to assume necessity. (See: "The Regularists' Trump Card - The Dissolution of the Problem of Free Will and Determinism" in section 5f Laws of Nature [Internet Encyclopedia of Philosophy])

Well, I am a compatibilist. That is, I find free will and determinism to be compatible. So, in relation to that section you just pointed out, I think I would be considered a regularist. Isn't that right?

@Night Ripper,

Night Ripper;137525 wrote:

Which has absolutely nothing to do with my previous post. Why don't you read what I wrote and reply to my question instead of talking over me?

Let me try again, would you like to explain (in 1 post, not 3 pages) exactly how the true statement...

"nothing ever has or ever will travel faster than the speed of light"

...entails that it's physically impossible?

Do you see anything in that question about laws? No. So don't repeat your irrelevant claim: "A physical impossibility is that which is contrary to known physical laws."

Answer MY question, not some imagined question.

---------- Post added 03-08-2010 at 12:03 PM ----------

You'll have to give me the entire argument so I can explain where your mistake is. Right now you're just retreating to an argument you can't even write out.

I don't know the entire argument. What I do know is that it is a consequence of the theory of relativity that nothing travels faster than the speed of light. Perhaps you don't believe this. Then I suggest you learn something about relativity theory. But, supposing it is true that it is a consequence of the theory of relativity that nothing travels faster than light, it follow that it is physically impossible for something to travel faster than the speed of light.

So, to make the argument plain:

1. If relativity theory implies that nothing travels faster than the speed of light, then it is physically impossible for anything to travel at the speed of light.
2. Relativity theory implies that nothing travels faster than the speed of light.

Therefore, 3, it is physically impossible for anything to travel at the speed of light.

Now, do I understand that your objection to the above argument is that I have not shown that premise 2 is true? I thought it was a matter of common knowledge among educated people that premise 2 is true. So, I can draw only one of two conclusions.

Anyway, that is where we stand. Either you think that 2 is false, and the above argument is unsound, or premise 2 is true, and the above argument is sound.

@kennethamy,

kennethamy;137580 wrote:

1. If relativity theory implies that nothing travels faster than the speed of light, then it is physically impossible for anything to travel at the speed of light.

Again, I think you're committing the modal fallacy. The claim "nothing travels faster than the speed of light" is not the same as "nothing can travel faster than the speed of light". It's the difference between doesn't and can't.

---------- Post added 03-08-2010 at 02:40 PM ----------

Zetherin;137577 wrote:

Well, I am a compatibilist. That is, I find free will and determinism to be compatible. So, in relation to that section you just pointed out, I think I would be considered a regularist. Isn't that right?

I think free will and regularity determinism are compatible but not free will and necessity determinism. So, I'm a sort of hybrid-compatibilist. I also think the fact that there's a third position (the one I'm taking) is not well recognized and might be why the disagreements seem so intractable.

@Night Ripper,

Night Ripper;137582 wrote:

Again, I think you're committing the modal fallacy. The claim "nothing travels faster than the speed of light" is not the same as "nothing can travel faster than the speed of light". It's the difference between doesn't and can't.

Not at all. To say that according to relativity theory, it is physically impossible for anything to travel at the speed of light is only to say that relativity theory and the proposition that something travels faster than light are incompatible. Isn't that true?

I am saying (A) that necessarily, if relativity theory is true, then it is false that something can travel faster than the speed of light.
I am not saying (B) that if relativity theory is true, then necessarily, nothing can travel at the speed of light.

Confusing (A) with (B). or inferring (B) from (A) would commit the modal fallacy. I am doing neither.

@kennethamy,

kennethamy;137586 wrote:

I am saying (A) that necessarily, if relativity theory is true, then it is false that something can travel faster than the speed of light.

Wrong. If relativity theory is true, then it is false that something does travel faster than the speed of light. The problem is your fallacious insertion of "can" in bold.

@Night Ripper,

Night Ripper;137587 wrote:

Wrong. If relativity theory is true, then it is false that something does travel faster than the speed of light. The problem is your fallacious insertion of "can" in bold.

That is true, but isn't it also true that anything traveling faster than light is incompatible with relativity theory? That is, it is impossible both for relativity theory to be true, and for something to travel faster than light. And that is what is meant by "it is physically impossible for anything to travel faster than light". Relativity theory and something traveling faster than light cannot both be true. Not merely, are not both true. Relativity theory and Berlin is the capital of Spain are not both true, but it is not the case that both cannot be true. A and B may not both be true, but it does not follow that they cannot both be true.

@Night Ripper,

N.R., how do you define "can" ? and "does" ?
Does "can" as possibility not implies potential existence and therefore "does" ?

@Fil Albuquerque,

Fil. Albuquerque;137591 wrote:

N.R., how do you define "can" ? and "does" ?
Does "can" as possibility not implies potential existence and therefore "does" ?

Many things can happen that do not happen, but not conversely.

@Fil Albuquerque,

...once more we arrive to the problem of hard determinism or soft determinism as a deep different conception of how reality does work...

Hard Determinism underlies this idea of communication, through Dialectic Necessity of relation between what "does" and what "can"...

@kennethamy,

kennethamy;137589 wrote:

That is, it is impossible both for relativity theory to be true, and for something to travel faster than light. And that is what is meant by "it is physically impossible for anything to travel faster than light".

No, that's not what is meant. If something is physically impossible then it can't happen.

@kennethamy,

kennethamy;137594 wrote:

Many things can happen that do not happen, but not conversely.

...I was referring "does" to past present and future...
What what can that will not happen ?

@Night Ripper,

Night Ripper;137599 wrote:

No, that's not what is meant. If something is physically impossible then it can't happen.

But remember:

"In contrast, when Regularists say that some situation is physically impossible - e.g. that there is a river of cola - they are claiming no more and no less than that there is no such river, past, present, future, here, or elsewhere. There is no nomic dimension to their claim. They are not making the modal claim that there could not be such a river; they are making simply the factual (nonmodal) claim that there timelessly is no such river. (Further reading: 'The' Modal Fallacy.)"

@Fil Albuquerque,

Fil. Albuquerque;137591 wrote:

N.R., how do you define "can" ? and "does" ?
Does "can" as possibility not implies potential existence and therefore "does" ?

physically existent = "does happen"
physically nonexistent = "doesn't happen"
physically possible = "can happen"
physically impossible = "can't happen"
physically necessary = "must happen"

Obviously, anything that does happen, can happen. However, we don't observe that something must happen when it does happen. We don't observe that something can't happen when it doesn't happen. There's no way to test that anything must or can't happen.

Zetherin;137603 wrote:

But remember:

"In contrast, when Regularists say that some situation is physically impossible - e.g. that there is a river of cola - they are claiming no more and no less than that there is no such river, past, present, future, here, or elsewhere. There is no nomic dimension to their claim. They are not making the modal claim that there could not be such a river; they are making simply the factual (nonmodal) claim that there timelessly is no such river. (Further reading: 'The' Modal Fallacy.)"

He's adopting different definitions for terms that people usually define as I have above. It confuses people so I don't do it.

---------- Post added 03-08-2010 at 03:44 PM ----------

Fil. Albuquerque;137601 wrote:

...I was referring "does" to past present and future...
What what can that will not happen ?

When I say does, I mean it timelessly. If I say that nothing does travel faster than the speed of light, I mean ever. We're simply taking that as universally true for the sake of argument.

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