Ask a physicist anything. (2)

[Doveaman]

Flowing....around the marble, I guess. I wasn't thinking of it moving necessarily.

I almost misunderstood this statement to mean the water is flowing, but not moving.

If the water is flowing "around" the marble, which direction is it flowing?

 

[Wiccan_Child]

We could only imagine this sheet if we imagined gravity pulling down on the object to create the dent in the sheet.

As far as our imagination can see, it is gravity causing the dent, and not the dent causing the gravity.

It's an analogy. An actual rubber sheet would be dented by gravity. The point is that space is dented by mass, and we perceive that dent to be gravity. The Earth's mass causes a dent in space that causes other masses to 'roll' towards it, much as a marble on a rubber sheet will roll towards a massive object. That the rubber sheet analogy employs gravity is irrelevant.

That's because gravity is acting upon us independently of the well.

Even apart from the well we still need energy to go 'up' or be compelled to stay down.

Not without the well we wouldn't. What would compel us down?

So the earth is in the gravity well of the universe, and we are in the gravity well of the earth.

If the earth has its own gravity well, then where's the dent?

In space. Ever object of mass dents the space around it. When you have many masses grouped together, their individual dents aggregate to form a big dent (imagine many marbles spread out over a sheet of rubber, and compare that to many marbles grouped together).

The galaxy's gravity well is enormous, but spread out. Think of us as a large marble slowly precessing round the lip of a large valley, and we create a little dent in our local part of the sheet. That's how the Earth's and the galaxy's gravity wells interact.

Obviously, space is three-dimensional, so it's a little more tricky than that, but that's the basic idea.

 

[Wiccan_Child]

Well, it's not my fault. It's the rubber sheet's fault. I'm just trying to make sense of it.

Isn't science supposed to provide the "best" explanations? If this is the best you've got, I just don't get it.

'Best' doesn't mean 'universally comprehensible'. It means 'most likely to be true'. The universe is under no geas to be understandable to the human brain; after all, we only evolved to comprehend things that would happen to us, which is a tiny fraction of what actually happens in the universe (hence why relativity and quantum mechanics are counter-intuitive).

 

[Doveaman]

It's an analogy.

Does this mean it's not science?

Can these "dents" in space be empirically verified?

An actual rubber sheet would be dented by gravity. The point is that space is dented by mass, and we perceive that dent to be gravity. The Earth's mass causes a dent in space that causes other masses to 'roll' towards it, much as a marble on a rubber sheet will roll towards a massive object.

I don't feel like I'm rolling. Do you?

That the rubber sheet analogy employs gravity is irrelevant.

The rubber sheet analogy employs gravity because the rubber sheet analogy is lacking on scientific explanation, hence the need to employ gravity to make sense of it.

Which brings us back to my first post: "The usual demonstration using heavy steel balls on a rubber sheet to represent ‘gravity wells’ relies on gravity as its own explanation!"

Not without the well we wouldn't. What would compel us down?

The same thing that compels the steel ball down onto the rubber sheet – Gravity.

In space. Ever object of mass dents the space around it. When you have many masses grouped together, their individual dents aggregate to form a big dent (imagine many marbles spread out over a sheet of rubber, and compare that to many marbles grouped together).

I’m tempted to ask why we are not all bunched together like many marbles grouped together in a big dent, but I’m not going to ask.

The galaxy's gravity well is enormous, but spread out. Think of us as a large marble slowly precessing round the lip of a large valley, and we create a little dent in our local part of the sheet. That's how the Earth's and the galaxy's gravity wells interact.

Obviously, space is three-dimensional, so it's a little more tricky than that, but that's the basic idea.

Well, thanks for nothing.

 

[Doveaman]

'Best' doesn't mean 'universally comprehensible'. It means 'most likely to be true'. The universe is under no geas to be understandable to the human brain; after all, we only evolved to comprehend things that would happen to us, which is a tiny fraction of what actually happens in the universe (hence why relativity and quantum mechanics are counter-intuitive).

Are you talking to me?

Because my granddad was not an ape, nor am I.

 

[pgp_protector]

Are you talking to me?

Because my granddad was not an ape, nor am I.

Psst, yes, Humans are classified as Apes, are you not a Homosapien?

Humans are bipedal primates belonging to the species Homo sapiens (Latin: "wise man" or "knowing man") in Hominidae, the great ape family. They are the only surviving members of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving. This mental capability, combined with an erect body carriage that frees the arms for manipulating objects, has allowed humans to make far greater use of tools than any other species. Mitochondrial DNA and fossil evidence indicates that modern humans originated in Africa about 200,000 years ago. Humans are widespread in every continent except Antarctica, with a total population of 6.8 billion as of November 2009.

 

[Wiccan_Child]

Does this mean it's not science?

It means it's an educational aid to help the unwashed masses grasp an otherwise abstract and complicated idea. Scientists acquired funding for the LHC by explained the Higgs Boson to politicians, not as science actually understands it, but by a simplistic analogy.

Do you honestly not understand the difference between an idea, and an analogy of an idea?

Can these "dents" in space be empirically verified?

Yes: the theory that predicts them predicts other phenomena as well. Vindicating this other phenomena vindicates the underlying theory, and, thus, all the other phenomena it predicts by proxy. Or, more simply, the dents are empirically manifested by the very existence of gravity. Surely you don't doubt that, if I jump off the Empire State Building, I will fall to the ground?

I don't feel like I'm rolling. Do you?

I can feel my chair pushing into my backside (if you'll pardon the image), which implies that my body is pushing into the chair, which implies I'm rolling down the potential well. So yes, I do feel like I'm rolling.

The rubber sheet analogy employs gravity because the rubber sheet analogy is lacking on scientific explanation, hence the need to employ gravity to make sense of it.

Why would an analogy need a scientific explanation? It's an analogy. It's a system that superficially resembles another system. The ins and outs of the former is utterly irrelevant; it has absolutely no bearing on the veracity of the latter.

Which brings us back to my first post: "The usual demonstration using heavy steel balls on a rubber sheet to represent ‘gravity wells’ relies on gravity as its own explanation!"

And as we've all been trying to tell you, that's completely and utterly irrelevant. It's an analogy. It's not meant to be a perfect replica. It's meant to give a simple, visual explanation of why a moving particle will accelerate towards warped space.

The same thing that compels the steel ball down onto the rubber sheet – Gravity.

Since you've hypothesised the wells away ("That's because gravity is acting upon us independently of the well. Even apart from the well we still need energy to go 'up' or be compelled to stay down."), and since the wells are what cause the phenomenon we call 'gravity', you are wrong.

I’m tempted to ask why we are not all bunched together like many marbles grouped together in a big dent, but I’m not going to ask.

We are. Haven't you noticed?

Well, thanks for nothing.

I'd ask if you understood the analogy, but it seems you don't understand the very concept of an analogy.

Are you talking to me?

My granddad was not an ape, nor am I.

Your biology begs to differ. You share a common ancestor with all extant ape species, and that ancestor was an ape. Therefore, according to scientific vernacular, you are an ape.

You're welcome to redefine words and play semantic games, of course, but, according to science, you are an ape.

 

[Wiccan_Child]

Psst, yes, Humans are classified as Apes, are you not a Homosapien?

Of course, he's not, he has Sin Nature™!

Oh, wait, that's AV.

 

[pgp_protector]

Think of it this way
analogy = parable.
Neither one is 100% accurate / true, but help to explain what is going on.

 

[lordworshipper]

Isn't whether or not we are apes or descended from them off topic? I mean, this is about physics not biology.

 

[pgp_protector]

Isn't whether or not we are apes or descended from them off topic? I mean, this is about physics not biology.

Ask a Physicist Anything

 

[lordworshipper]

Okay, fair enough.

What do you think came before the big bang? Absolutely nothing? Or do you support the string or other theories?

 

[AV1611VET]

Psst, yes, Humans are classified as Apes, are you not a Homosapien?

No, I am not --- and it's "Homo sapiens".

 

[AV1611VET]

Of course, he's not, he has Sin Nature™!

Oh, wait, that's AV.

I'm not a sinner because I sin; I sin because I'm a sinner.

 

[Wiccan_Child]

Isn't whether or not we are apes or descended from them off topic? I mean, this is about physics not biology.

This is about anything. You ask a question, and we (by which I mean, me, and anyone else who wants to answer) attempt an answer. The idea is to be physics-y, but I'm more than happy for this to turn into an explain-evolution-to-me thread.

Ask a Physicist Anything

Bingo.

Okay, fair enough.

What do you think came before the big bang? Absolutely nothing? Or do you support the string or other theories?

My pet hypothesis, which is by no means supported by any evidence, is that the universe came into being because, before it existed, there was no reason for it not to exist, so POOF it became.

In other words, a quantum fluctuation in a region (for want of a better word) without anything inhibiting such an event. Causality has been put through the wringer in light of modern scientific advances, so I don't put much truck in what my intuition tells me.

 

[Wiccan_Child]

No, I am not --- and it's "Homo sapiens".

Technically, it's Homo sapiens sapiens, but now we're just splitting hairs.

I'm not a sinner because I sin; I sin because I'm a sinner.

Don't you have free will? Can't you simply not perform any sinful act? Or is the mere act of being born human sinful in itself?

 

[canehdianhotstuff]

Well if your Catholic, original sin still exist on you when you are born, hence baptism.

Humans are inherently evil. Therefore sin.

 

[AV1611VET]

Technically, it's Homo sapiens sapiens, but now we're just splitting hairs.

So he was doubly wrong?

Don't you have free will?

Yes.

Can't you simply not perform any sinful act?

"Any sinful act" is the key here; but we cannot get to the point where we claim 'we have no sin'.

If we say that we have not sinned, we make him a liar, and his word is not in us.

We have what is called "sins of commission" and "sins of omission".

But --- hypothetically --- if we were to be born and not since even once, we would still go to Hell for carrying the Sin Nature in our flesh.

Or is the mere act of being born human sinful in itself?

No.

 

[Wiccan_Child]

So he was doubly wrong?

Pretty much, though it's clear what he meant. It's like when someone says the Big Bang was the start of the universe; though that's not what the theory actually says, it's good enough.

"Any sinful act" is the key here; but we cannot get to the point where we claim 'we have no sin'.

We have what is called "sins of commission" and "sins of omission".

What are they?

But --- hypothetically --- if we were to be born and not since even once, we would still go to Hell for carrying the Sin Nature in our flesh.

This is inherited from Adam and Eve, right?

No.

But Sin Nature makes it so that babies are born sinners, right? If so, what happens when a baby dies? Presumably they can't accept Jesus into their hearts (or whatever), so do they go to hell?

 

[AV1611VET]

Pretty much, though it's clear what he meant. It's like when someone says the Big Bang was the start of the universe; though that's not what the theory actually says, it's good enough.

I believe "Big Expansion" would be a better term.

According to the Bible, the universe will end with a "big bang".

What are they?

A sin of commission is an act we commit that we shouldn't; a sin of omission is an act we don't commit that we should.

This is inherited from Adam and Eve, right?

Just Adam.

But Sin Nature makes it so that babies are born sinners, right?

Yes, but there's a technicality with babies; see below.

If so, what happens when a baby dies? Presumably they can't accept Jesus into their hearts (or whatever), so do they go to hell?

No --- a baby is born a sinner, but in a state of innocence.

When a baby (or mentally-challenged) person dies, they will be accepted into Heaven on a technicality.

We call this technicality "the age of accountability" --- that time in a person's life when they know and understand right from wrong.