**Ask a monkey a physics question thread**

[OngBonga]

"a round plane figure whose boundary (the circumference) consists of points equidistant from a fixed point (the center)"

So define round.

Is a regular 1,000,000 sided polygon a circle? It will certainly fit the description of "round" if that's a loose term.

[OngBonga]

This is an nteresting read...

http://einstein.stanford.edu/TECH/technology1.html

The roundest thing we ever made... a gyroscope. This particular gyroscope has roundness so perfect that the only thing we know of that is more spherical is a neutron star.

There's an interesting point that says that if that gyroscope were to be scaled up to Earth size, then the tallest mountains would be 8 feet tall.

That shows both the incredible level of perfection they've achieved, and that the imperfections still exist in something so amazingly spherical.

[OngBonga]

The closest thing in physics would be something like the surface of a neutron star or the equator of a black hole's event horizon. The problem here is that you are kinda really talking about smoothness, and if you think circular has a tricky definition, then you'll find "smooth" to be even more fundamentally fun.

Yeah that was the impression I got. Note that the gyroscope talked of in the article I linked is only surpassed in roundness by neutron stars.

I think they omitted event horizons simply because of the uncertainty in that regard. Hawking has muddied the waters by suggesting there could be wild fluctuations going on.

[OngBonga]

pfft I googled it in shock that anyone would be so absurd to suggest a circle is not a polygon, and it fucking well isn't because a polygon has straight edges, apparently.

I thought a polygon was simply a "many sided shape", from three to infinity, from a traingle to a circle.

Ok, but the ratio aspects are the key to my definition. It has to be exactly pi, and the shape has to be perfectly regular.

[MadMojoMonkey]

pfft I googled it in shock that anyone would be so absurd to suggest a circle is not a polygon, and it fucking well isn't because a polygon has straight edges, apparently.

I thought a polygon was simply a "many sided shape", from three to infinity, from a traingle to a circle.

Ok, but the ratio aspects are the key to my definition. It has to be exactly pi, and the shape has to be perfectly regular.

Lol.
Made me think the phonetic combination of sounds, "monogon," which I'm now wondering if it's already a word that means circle.

***
Monogon sounds decidedly like some anatomical word.

... flows through the perpendicular arterial flagellum to the monogon region of the oblong hypothesis...

[a500lbgorilla]

I agree that circles are infinity sided polygons and I don't much care if the words miss the meaning.

Compasses don't make perfect circles, neither do mathematical series. Nothing makes perfect circles because they don't exist but in our estimation of things.

Maybe an electron can somehow be a perfect circle.

[a500lbgorilla]

Maybe sinusoidal waves like light are a kind of perfect circle.

[MadMojoMonkey]

Well, you're ignoring that those series are infinite, and that the infinite series do, indeed, equal what they claim to equal.
(Assuming they aren't complete nonsense.)

Don't get tripped up by the fact that any finite number, no matter how big, is an infinitesimal when compared to infinity.

Any polygon with a finite number of sides is def. not a circle. The idea that a polygon can have infinite number of sides is only meaningful in the sense of a limit. It seems reasonable that circle = limit as N goes to infinity of N-gon.

However, I'm not sure it's the best definition of a circle. Perhaps it has it's uses. There are many, many ways to define a circle mathematically and some are more robust than others, some are more useful for specific applications than others.

[a500lbgorilla]

Any polygon with a finite number of sides is def. not a circle. The idea that a polygon can have infinite number of sides is only meaningful in the sense of a limit. It seems reasonable that circle = limit as N goes to infinity of N-gon.

Oh shit, calculus.

There is something to say about the idea of a perfect circle. It certainly comes up a lot and has many uses.

[a500lbgorilla]

(Mathematical) Series are not things. They live in a space where the rules allow for infinite steps.

[MadMojoMonkey]

(Mathematical) Series are not things. They live [...].

:/

Don't make me ask you to define "things." That sounds tedious. Can we agree that we're talking about series as a noun and just agree that, whether person, place, thing, or idea... it's one of those.

[a500lbgorilla]

:/

Don't make me ask you to define "things." That sounds tedious. Can we agree that we're talking about series as a noun and just agree that, whether person, place, thing, or idea... it's one of those.

I'd gladly do it though.

Whatever exists is a thing.

[MadMojoMonkey]

They live in a space where the rules allow for infinite steps.

Zeno's paradox shows that we do indeed live in a similar space.

Although, having glanced at the wiki page... seems like my interpretation isn't the popular one.

I always assumed that the whole... in order to get anywhere, you have to first get half-way there. Then, in order to cover the remaining half, you must first get half-way across that... ad infinitum. The conclusion is that it takes an infinite number of steps to get anywhere and ain't nobody got time for that.

However, that conclusion is clearly false. People "get there" all the time. Not just people, even.

So a more appropriate conclusion would be that it's all too common for something modeled as taking an infinite number of steps to be concluded in a finite length of time. The only requisite is that the length of time it takes between completion of steps reduces "fast enough" to allow for a "reasonable" amount of time needed for completion.

EDIT: "Fast enough" means that it converges as x goes to + infinity.
(At some point, someone was wondering why they had to learn about convergence. Here's an example of usage.)

[a500lbgorilla]

So a more appropriate conclusion would be that it's all too common for something modeled as taking an infinite number of steps to be concluded in a finite length of time. The only requisite is that the length of time it takes between completion of steps reduces "fast enough" to allow for a "reasonable" amount of time needed for completion

I would say that is much more reasonable to see infinity as funny idea but just an idea.

[MadMojoMonkey]

I would say that is much more reasonable to see infinity as funny idea but just an idea.

I don't see how this couldn't be said for all of mathematics.

The number 1 is a funny idea, but just an idea.

[a500lbgorilla]

I don't see how this couldn't be said for all of mathematics.

The number 1 is a funny idea, but just an idea.

Yeah, I agree completely.

What is the number 1?

[OngBonga]

I would say that is much more reasonable to see infinity as funny idea but just an idea.

Infinity exists in the real world.

What's the density of a singularity with a mass of >0?

[a500lbgorilla]

Infinity exists in the real world.

What's the density of a singularity with a mass of >0?

If I told you 12, how would you show me wrong?

[a500lbgorilla]

So a more appropriate conclusion would be that it's all too common for something modeled as taking an infinite number of steps to be concluded in a finite length of time. The only requisite is that the length of time it takes between completion of steps reduces "fast enough" to allow for a "reasonable" amount of time needed for completion.

EDIT: "Fast enough" means that it converges as x goes to + infinity.
(At some point, someone was wondering why they had to learn about convergence. Here's an example of usage.)

OK, if a thing needs finite time to render, the only place that infinity ever pops up is in your head.

[a500lbgorilla]

Zeno's paradox shows that we very much don't. Draw any finish line and watch me cross it.

[a500lbgorilla]

How can you claim to live in a paradoxical world?

Pick any paradox. How can it be true of the world that you're a part of? Paradoxes are just what happen when human brains try to put human rules to an inhuman universe.

[MadMojoMonkey]

How can you claim to live in a paradoxical world?

Seems easy enough. I could take those words you just used and slightly rearrange them, throwing in some personal pronouns.

I wouldn't do that, though. Just because a thing is called a paradox, that doesn't mean the universe is messed up. I cited Zeno's paradox, then explained how it's not a contradiction.

[a500lbgorilla]

Seems easy enough. I could take those words you just used and slightly rearrange them, throwing in some personal pronouns.

I wouldn't do that, though. Just because a thing is called a paradox, that doesn't mean the universe is messed up. I cited Zeno's paradox, then explained how it's not a contradiction.

But you're just shuffling words. Words are the things we use to share ideas with one another.

Zeno's paradox shows how people can stumble into problems that aren't there.

[OngBonga]

Let me put it another way.

If you reject infinity as a real world thing, then you reject the singularity.

That's not absurd, in fairness. There's debate about that according to google.

[a500lbgorilla]

Let me put it another way.

If you reject infinity as a real world thing, then you reject the singularity.

That's not absurd, in fairness. There's debate about that according to google.

I reject our ability to describe the singularity.

[OngBonga]

The singularity is pretty well defined, as far as I'm aware. It's a region of mass with zero volume in space. If it has volume, it ceases to be a singularity. And if it has no mass, then it has zero density, not infinity.

[a500lbgorilla]

The singularity is pretty well defined, as far as I'm aware. It's a region of mass with zero volume in space. If it has volume, it ceases to be a singularity. And if it has no mass, then it has zero density, not infinity.

OK, define it all you like.

PS, your definition ain't right.

Man, I wanted to explain my understanding of the singularity by explaining protons all the way up the iron-burning stars then supernova then black holes but I just don't have the strength.

[MadMojoMonkey]

The singularity is pretty well defined, as far as I'm aware. It's a region of mass with zero volume in space. If it has volume, it ceases to be a singularity. And if it has no mass, then it has zero density, not infinity.

The mathematical notion of a singularity or "pole" is well understood.

If we're talking black holes, then Einstein's field equations predict a singularity in spacetime. Bu... bu... but... that mass is there 'cause particles, right? And them's particles have an astoundingly well defined location, right? So how can they have well-defined momentum and just sit there... being a singularity, then?

huh
?

GR and QM just don't overlap well, and the only thing to say is ... dunno.

We don't need to go to black holes to find a singularity, though.

Electrons have charge, obv. Electrons have no discernible size. At best, though astoundingly thorough predictions and measurements, we can say that if the electron has a non-0 radius, it can not be more than 10^-18 m. So for all that we have measured, there is a singularity in the electric field at the location of the electron.

Bu... bu... but... Where is that electron? QM... you make me cry sometimes.

We haven't proven ourselves clever enough to actually measure the E-field that precisely. The universe has decided that electrons will not sit still for photos, and so it must be.

[Keith]

The singularity is pretty well defined, as far as I'm aware. It's a region of mass with zero volume in space. If it has volume, it ceases to be a singularity. And if it has no mass, then it has zero density, not infinity.

Can it have density if it has no volume?

[OngBonga]

Can it have density if it has no volume?

idk, ask mojo, I can only answer questions directed at mojo.

As for the falling thing, well I remember as a kid watching a tv programme where they threw eggs out of a plane in an effort to not break one, I think it was probably Record Breakers with that dude who died of lung cancer thanks to passive smoking. Roy Castle, that's his name. I digress. They eventually succeeded from what one would consider a ridiculous height considering it's an egg, the egg that made it hit a hill at exactly the right angle to basically continue its fall coming to a gradual halt, rather than hitting the ground perpendicular. So yeah I reckon it's doable if all factors are precisely correct, based on eggs.

edit - I just remembered they were putting a lot spin on the egg as they threw it, so if you ever find yourself falling out of a plane with no parachute, aim for a hill and attempt to get yourself spinning in the air in the direction you'll go down the hill.

[MadMojoMonkey]

idk, ask mojo, I can only answer questions directed at mojo.

lol

So yeah I reckon it's doable if all factors are precisely correct, based on eggs.

-.-
Not sure if it's physics or if it just sounds like physics.

Anyway, this throws a kink in wuf's question, because I thought it was implied that the jumper hit the ground perpendicular to their velocity... I.e. a square hit. If they're allowed to land on a curved slope, then that changes everything. The only thing to protect against is friction burns, then.

edit - I just remembered they were putting a lot spin on the egg as they threw it, so if you ever find yourself falling out of a plane with no parachute, aim for a hill and attempt to get yourself spinning in the air in the direction you'll go down the hill.

This is what a baseball pitcher does to throw a curve ball. The pitcher puts forward spin on the ball, causing the Magnus effect to pull the ball downward by deflecting the air flowing under the ball such that the air goes upward. Newton's 3rd says that if the ball pushes the air upward, then the air pushes the ball downward, making it curve toward the ground faster than gravity would normally pull it down.

You'd want to spin the other way to exploit the Magnus effect. This would send the air going above you toward the ground. Which would exchange your forward velocity for lift, reducing your rate of falling.

Unfortunately, the Magnus Effect tends to "spin up" the object. Once you start the rotation, it gets amplified. You might have more trouble keeping your limbs in close and not flailing wildly. The flailing would probably not be best for an injury free landing.

[OngBonga]

This is what a baseball pitcher does to throw a curve ball. The pitcher puts forward spin on the ball, causing the Magnus effect to pull the ball downward by deflecting the air flowing under the ball such that the air goes upward. Newton's 3rd says that if the ball pushes the air upward, then the air pushes the ball downward, making it curve toward the ground faster than gravity would normally pull it down.

You'd want to spin the other way to exploit the Magnus effect. This would send the air going above you toward the ground. Which would exchange your forward velocity for lift, reducing your rate of falling.

Unfortunately, the Magnus Effect tends to "spin up" the object. Once you start the rotation, it gets amplified. You might have more trouble keeping your limbs in close and not flailing wildly. The flailing would probably not be best for an injury free landing.

I think it was back spin, so when it hit the ground, the spin attempts to cause it to roll uphill. Of course, the spin is utterly overwhelmed by gravity, but the tiny effect it has could be the difference between it breaking and not.

Or maybe it was top spin so it hit the ground and immediately rolled quickly down the hill.

I'm pretty sure the spin is intended to help with the roll though, and not reduce its velocity.

[MadMojoMonkey]

Can it have density if it has no volume?

No and yes. This question is a bit trickier than it seems at first glance.


No because you're talking about mass density and implicitly talking about mass per unit volume. I'm not entirely sure if there are any substances which would allow us to talk about mass per unit area as such. Maybe the electrons in graphene?


Yes because mass density isn't the only kind of density worth discussing.

For that matter, electrons have measurable mass and charge, but no measurable volume. We have put limits on the biggest an electron can be, given our subtle observations, but we have yet to prove either that they have small size or that they have 0 size. Turns out that proving a measurement is exactly 0 is easier said than done.

If you're talking about a conductor with a net charge, then talking about the charge density of the conductor still doesn't really make sense, because all the net charge is located at the surface of the conductor. So when we talk about the charge density in that case, we're really talking about charge per unit area.

The same could be said for charge on a line, but in that case, we're making an idealization since there is no truly 1D conductor.

[OngBonga]

The math breaks down with the singularity. It's not the infinity that's a real problem, it's that our ability to describe the real problem is lacking.

If the maths breaks down, and the singularity exists in the physical world, why do you not see this as evidence of infinity in the physical world?

[a500lbgorilla]

If the maths breaks down, and the singularity exists in the physical world, why do you not see this as evidence of infinity in the physical world?

Calling it a singularity doesn't make it a singularity.

[MadMojoMonkey]

OK, if a thing needs finite time to render, the only place that infinity ever pops up is in your head.

I'm not sure I follow you here.

Are you saying that if any (real) process is completed in a finite number of steps, then infinity is a human construct?

Whether or not math is a property of the universe or a construct of minds is a maddeningly philosophical debate. There's something interesting to the fact that people who have never met can have nonetheless worked out the same language (math) on their own.

Whether or not infinity is an invention of humanity, it is a wildly useful concept which we use to make real, observable predictions about the universe.

[a500lbgorilla]

Whether or not infinity is an invention of humanity, it is a wildly useful concept which we use to make real, observable predictions about the universe.

Share them with me.

[MadMojoMonkey]

Share them with me.

When a particle encounters a boundary, it has a probability of "quantum tunneling" through said barrier. The solution to the wave function describing the particle experiences exponential decrease in the "forbidden" region which is the barrier.

The solution for that region is of the form
A*exp(x) + B*exp(-x)
but we can immediately rule out one of the terms, because we are going to integrate the square of the solution of the Schroedinger (to tease out ANY measurable quantity from it) from -inf to inf, i.e. over all space. In math speak, "We require all physical solutions to the Schroedinger equation to have finite L^2 norm."

So if we decide the particle is moving in the positive x-direction when it encounters this boundary, then we can rule out that part of the solution with exp(x), since that "blows up" as x goes to infinity.

So right there, we assumed that x can go to infinity, and we ruled out an entire class of mathematically viable solutions.

Then again, when we integrate the square of exp(-x) from {ongbonga} to infinity, we solve the definite integral setting exp(-inf) = 0, and we get our solution.

The solution we find uses this assumption of infinity twice and yields results correct to absurdly high degrees.

This is for the most simple cases of the SE. In general, the solutions exist in infinite-dimensional space. For instance... What is the minimum energy the electron can have in a Hydrogen atom? -13.6 eV. What's the max? Well... if it's 0, then the electron is no longer bound to the proton and it's no longer rightly an atom. There is no theoretical "highest energy level" or "biggest shell" the electron can occupy. So the solutions to the state of an electron in a Hydrogen atom exist in infinite dimensions.

[a500lbgorilla]

When a particle encounters a boundary, it has a probability of "quantum tunneling" through said barrier. The solution to the wave function describing the particle experiences exponential decrease in the "forbidden" region which is the barrier.

The solution for that region is of the form
A*exp(x) + B*exp(-x)
but we can immediately rule out one of the terms, because we are going to integrate the square of the solution of the Schroedinger (to tease out ANY measurable quantity from it) from -inf to inf, i.e. over all space. In math speak, "We require all physical solutions to the Schroedinger equation to have finite L^2 norm."

So if we decide the particle is moving in the positive x-direction when it encounters this boundary, then we can rule out that part of the solution with exp(x), since that "blows up" as x goes to infinity.

So right there, we assumed that x can go to infinity, and we ruled out an entire class of mathematically viable solutions.

Then again, when we integrate the square of exp(-x) from {ongbonga} to infinity, we solve the definite integral setting 1/exp(-inf) = 0, and we get our solution.

The solution we find uses this assumption of infinity twice and yields results correct to absurdly high degrees.

This is for the most simple cases of the SE. In general, the solutions exist in infinite-dimensional space. For instance... What is the minimum energy the electron can have in a Hydrogen atom? -13.6 eV. What's the max? Well... if it's 0, then the electron is no longer bound to the proton and it's no longer rightly an atom. There is no theoretical "highest energy level" or "biggest shell" the electron can occupy. So the solutions to the state of an electron in a Hydrogen atom exist in infinite dimensions.

No top. But also, no one ever gets to the top. We use infinity but that doesn't make infinity a thing.

[a500lbgorilla]

No top. But also, no one ever gets to the top. We use infinity but that doesn't make infinity a thing.

Well, I should say, if we use it...

Touche.

[OngBonga]

Whether or not math is a property of the universe or a construct of minds is a maddeningly philosophical debate.

Seems pretty clear cut to me... for us to "invent" something so exact is absurd. We only create the system of which we understand maths... ie decimal, binary, etc.

The concept one 1, 2, etc... the earth and the moon make two... there are two things there... whatever word or symbol you wish to use for two, however you interpret two, there will never be someone who sees three things there unless to them three is the word they use for two.

Maths is the language of nature.

[OngBonga]

So tell me what a singularity is.

[a500lbgorilla]

So tell me what a singularity is.

I don't know.

Who'd a-thunk I wouldn't understand whatever a singularity might be?

[a500lbgorilla]

There's no reason to believe that because you understand everything you understand, that you therefore understand everything.

Sometimes, you've got to accept that you just don't know.

[OngBonga]

Ok let's invent a word.

ongbongularity - a gravitational presence (mass >0) with zero volume in spacetime.

The ongbongularity might or might not be the same as a singularity, that is irrelevant.

Do you believe such a thing can exist in the physical universe? Or is my definition amibuous in ways I'm not aware of?

[a500lbgorilla]

Ok let's invent a word.

ongbongularity - a gravitational presence (mass >0) with zero volume in spacetime.

The ongbongularity might or might not be the same as a singularity, that is irrelevant.

Do you believe such a thing can exist in the physical universe? Or is my definition amibuous in ways I'm not aware of?

No. I don't give a hoot about definitions or words or the nonense of other people.

[a500lbgorilla]

The mathematical notion of a singularity or "pole" is well understood.

If we're talking black holes, then Einstein's field equations predict a singularity in spacetime. Bu... bu... but... that mass is there 'cause particles, right? And them's particles have an astoundingly well defined location, right? So how can they have well-defined momentum and just sit there... being a singularity, then?

huh
?

GR and QM just don't overlap well, and the only thing to say is ... dunno.

We don't need to go to black holes to find a singularity, though.

Electrons have charge, obv. Electrons have no discernible size. At best, though astoundingly thorough predictions and measurements, we can say that if the electron has a non-0 radius, it can not be more than 10^-18 m. So for all that we have measured, there is a singularity in the electric field at the location of the electron.

Bu... bu... but... Where is that electron? QM... you make me cry sometimes.

We haven't proven ourselves clever enough to actually measure the E-field that precisely. The universe has decided that electrons will not sit still for photos, and so it must be.

Yeah, I'm a fan of non-human ideas. Like measuring things in terms of other things.

How much of what you just said misses that mark?

[a500lbgorilla]

Yeah, I'm a fan of non-human ideas. Like measuring things in terms of other things.

How much of what you just said misses that mark?

And I mean to say a check. How much of what you just talked about is an unchecked story?

None of it.

[MadMojoMonkey]

And I mean to say a check. How much of what you just talked about is an unchecked story?

None of it.

whew.

[a500lbgorilla]

whew.

LOL

[MadMojoMonkey]

Yeah, I'm a fan of non-human ideas. Like measuring things in terms of other things.

How much of what you just said misses that mark?

None of it.

What?

:/

None of it?

[OngBonga]

As far as I'm concerned, this is a discussion about whether or not the singularity exists, not whether or not it can be defined. I feel like rilla is muddying the waters with philosophy.

[a500lbgorilla]

As far as I'm concerned, this is a discussion about whether or not the singularity exists, not whether or not it can be defined. I feel like rilla is muddying the waters with philosophy.

I really enjoy philosophy.

[OngBonga]

I really enjoy philosophy.

Philosophy is cool, until you basically say "what is clearly defined is not clearly defined because philosophy".

It's like saying 1+1 does not = 2. I'm thinking "but it does, don't be silly".

[a500lbgorilla]

Philosophy is cool, until you basically say "what is clearly defined is not clearly defined because philosophy".

It's like saying 1+1 does not = 2. I'm thinking "but it does, don't be silly".

You keep simply saying that you know these things.

[a500lbgorilla]

You keep simply saying that you know these things.

Obviously there's infinity!

[MadMojoMonkey]

You keep simply saying that you know these things.

Well, if you accept that 1 means 1, then you also accept that + is worth exploring, then math.

The labels and names may be whatever, but the sequence 1, 2, 3, 4, 5, ... is there.

So the argument that 1 + 1 = 2 is a universal truth is interesting.
The question of whether or not it would be true if there were no mind to learn it is also interesting.

[a500lbgorilla]

And I already said they exist they're just, right now, outside of reason!

[OngBonga]

I'm sure infinity must exist in a black hole simply because light can't escape.

Light itself also experiences infinity. It experiences infinite time dilation and infinite space contraction, thus, from the photon's perspective, the universe is a 2d plane, and the photon is motionless [citation needed].

But we see a 3d, or 4d if you count time, world, and we can see the light moves along a trajectory.

[a500lbgorilla]

I'm sure infinity must exist in a black hole simply because light can't escape.

Light itself also experiences infinity. It experiences infinite time dilation and infinite space contraction, thus, from the photon's perspective, the universe is a 2d plane, and the photon is motionless [citation needed].

But we see a 3d, or 4d if you count time, world, and we can see the light moves along a trajectory.

You won't escape Earth. Is Earth's grip on you infinite or simply over some threshold/limit?

Also, to the idea of the photon and it's infinite experience of time - you're literally saying that

a PHOTON

EXPERIENCES

INFINITE

TIME

and that this idea passes effortlessly through your mind with no problems.

[OngBonga]

...and that this idea passes effortlessly through your mind with no problems.

I guess I don't demand a full understanding of a concept in order for me to accept it as fact.

Light exists. I can see that. It travels at light speed, by definition. Our mathematical understanding of time dilation implies that at light speed, time dilation and space contraction are infinite. I'm not having a problem here. The only thing I might think is that maybe light speed is another theoretical concept, that actually the photon always travels at <c due to gravitational influences, and as such infinity is never actually attained.

But I don't have problems with accepting that light can experience time in a way that I can't understand.

[a500lbgorilla]

I guess I don't demand a full understanding of a concept in order for me to accept it as fact.

Light exists. I can see that. It travels at light speed, by definition. Our mathematical understanding of time dilation implies that at light speed, time dilation and space contraction are infinite. I'm not having a problem here. The only thing I might think is that maybe light speed is another theoretical concept, that actually the photon always travels at <c due to gravitational influences, and as such infinity is never actually attained.

But I don't have problems with accepting that light can experience time in a way that I can't understand.

I don't have problems with ideas when I need to use them.

But when I'm left to my dreams, I like thinking about thinking about thinking.

[OngBonga]

I feel like this is the difference between physics and philosophy...

physics is the attempt to understand the physical world,

philosophy is the attempt to not understand the physical world.

Like, the physician observes something and thinks "how can I understand this better", the philosopher thinks "how can I interpret this differently to how I observed it".

There's definitely a place for philosophy, but I'm not sure it's here, in teh physics thread, because it's too fucking ambiguous!

[a500lbgorilla]

I feel like this is the difference between physics and philosophy...

physics is the attempt to understand the physical world,

philosophy is the attempt to not understand the physical world.

Like, the physician observes something and thinks "how can I understand this better", the philosopher thinks "how can I interpret this differently to how I observed it".

There's definitely a place for philosophy, but I'm not sure it's here, in teh physics thread, because it's too fucking ambiguous!

HAHAHA same

[MadMojoMonkey]

It's hugely important to physics that there are highly trained physicists who ponder the philosophical completeness of what they understand.

It's hugely important to science that there are highly trained scientists who ponder the philosophical implications of the scientific process as a method of revealing True statements.

This helps the rest of the world understand what the professionals are saying and what they aren't saying. This helps the professionals pinpoint what they do and don't understand and offers clues as to what may be explored to expand understanding.

[Eric]

Why is there so much talk about holograms when looking at black holes?


I remember on the science channel or something awhile back they said no information is lost such that there is a hologram that shows info (I think this was in the context of someone entering a black hole). The recent http://www.dailymail.co.uk/sciencete...-surfaces.html article talks about black holes themselves being holograms as opposed to just the info that gets sucked into them.

[MadMojoMonkey]

Why is there so much talk about holograms when looking at black holes?


I remember on the science channel or something awhile back they said no information is lost such that there is a hologram that shows info (I think this was in the context of someone entering a black hole). The recent http://www.dailymail.co.uk/sciencete...-surfaces.html article talks about black holes themselves being holograms as opposed to just the info that gets sucked into them.

Preface: I may be not 100% aware of all the subtleties of the holographic principle.

The holographic principle is a statement which basically says that if some 3D thing can be wholly described using information in a 2D plane, then there is no rational reason to claim that the 3D description is more real than the 2d description.

If you can't tell whether you're looking at something which is 2D or 3D, that's kinda like looking at a holograph, hence the name "holographic principle."

I'm not aware of any use of the holographic principle outside of string theories. String theories are on the fringe of physics and are not a part of the Standard Model. Some of the most highly trained physicists in the world are trying to find a string theory which is a complete description of reality, but so far, they have not been able to do so.

String theories have shown and hinted at some interesting properties of the universe, but none of those properties was a new addition to the Standard Model, just a corner that hadn't been shown to be a part of the SM.

[OngBonga]

I've been reading about neutron stars, and apparently they can be virtually undetectable if they are not producing pulsars, or are not part of a binary system.

That said, how can we know that any "missing" matter in the universe is dark matter, and not simply neutron stars that we haven't yet found?

[MadMojoMonkey]

I've been reading about neutron stars, and apparently they can be virtually undetectable if they are not producing pulsars, or are not part of a binary system.

That said, how can we know that any "missing" matter in the universe is dark matter, and not simply neutron stars that we haven't yet found?

As ever, some people are blaming the WIMPS (weakly interacting massive particles), and ong is blaming the MACHOS (massive astrophysical compact halo objects).

Wimps are more likely than machos to be responsible for this one.

The distribution of dark matter is such that it would take a very high number of machos to account for it, and that would have a discernible effect on the light passing through them. Like, the sky looks blue because of light particles being redirected as they pass quite close to N2 molecules. Blue light is redirected the most (it's another 4th power relation), and the sky looks blue. Or something even more obvious like... darkness where light was blocked.

Keep in mind that a single neutron star is hard to detect, but you're talking about adding millions or billions of them to the solar system. If there were that many, it seems it'd be obvious that there were "particles" in the way of us looking at the galaxy.

EDIT:
This link to the astrophysical society says that there is some evidence for MACHOs. However, their data has ruled out the notion that dark matter is MACHOs. While there may be some MACHOs which contribute to the dark matter effects, they cannot be the whole explanation.

[OngBonga]

Keep in mind that a single neutron star is hard to detect, but you're talking about adding millions or billions of them to the solar system. If there were that many, it seems it'd be obvious that there were "particles" in the way of us looking at the galaxy.

I assume you mean Milky Way where you say Solar System. Obviously there's precisely zero neutron stars in the Solar System, such a presence would be easily detectable due to its gravitational influence on the Earth, moon, sun, et al.

That link just confuses me further. Honestly, I get the distinct impression that dark matter is just matter we know is there but haven't yet directly detected and classified, or profiled.

The fact we have WIMPs and MACHOs shows me that already we have two types of dark matter.

I feel like dark matter ceases to be dark matter when we see it.

[MadMojoMonkey]

I assume you mean Milky Way where you say Solar System.

Ugh. You got me.

That link just confuses me further. Honestly, I get the distinct impression that dark matter is just matter we know is there but haven't yet directly detected and classified, or profiled.

Well, we have detected it, that's why we gave it a name. We know that our current model of gravitation says the galaxies should rotate one way and that they observationally rotate in a different way.

So there's some force acting on/within galaxies which we weren't expecting. Maybe the theories which have so repeatedly NOT been disproved are not so good. Or maybe the data we've plugged into the theory is not so good.

We're pretty sure that gravity is mostly right (Einstein's gravity, that is), and if we adjust data in the equations we have which tell us the expected way the galaxies should rotate... if we fudge those by adding more mass, then it solves the issue quite well.

OK, so we saw a new observation, then made a prediction... and now we're searching for confirmation of that prediction... i.e. that there is a lot more mass in the galaxy than we've directly observed. How can that be? We are looking for this stuff and not finding it.

A) Where are we looking?
B) At the photons.
A) Maybe this stuff doesn't interact with photons.
B) All charged particles interact with photons.
A) Yeah, so maybe this stuff isn't charged and doesn't interact with electromagnetic fields at all.
B) OK... so how do we look for that?
A) Well, if it has mass, it will have gravitational effects.
B) Yeah. That's how this whole mess started.

The fact we have WIMPs and MACHOs shows me that already we have two types of dark matter.

I feel like dark matter ceases to be dark matter when we see it.

All too correct.

Except that dark matter is its name and, historically, it's hard to get physicists to not spout a prepared lecture on the history of physics at the drop of a dime. So like it or not, the phrase dark matter is going to be around for at least as long as luminiferous ether.

[OngBonga]

ugh, I just have more questions now and I feel like they're stupid questions, but hey I'll fire...

How can something not interact with electromagnetic fields while having gravity? Are we not to expect gravity and electromagnetism to one day be unified? Wherever there is electricity, there is magnetism, and vice versa, and the same can be said for time and space. So if gravity and EM are, in essence, one and the same, then why would one exist without the other? Why would dark matter not have an electromagnetic field to compliment its gravity field?

I now feel like dark matter implies gravity and EM are distinctly different forces, that they cannot be unified. But it's much more likely that I'm jumping to some rather extreme conclusions.

[OngBonga]

Just looking at dark energy to try and get my head around that.

Best I can imagine is that it's essentially tension. If one imagines the bedsheet anaolgy for gravity that we're all familiar with, well if one is to pull the sheet uniformly in each corner, it would lift the ball from its well... antigravity.

Can dark energy be viewed like this? That it's spacetime tension?

[OngBonga]

I also have some issues with the age of the universe.

I mean we're told it's 14 billion years or whatever.

I have to ask...

In whose frame of reference?

It seems to me that relativity utterly shits on the concept of the universe having an "age". As far as the photon that originated from the big bang is concerned, the universe is merely a fraction of a nanosecond old.

It just seems nonsense to say the universe is x amount of years old. Our concept of time is way too limited for it to mean anything.

Where does 14 billion years come from?

[OngBonga]

For the same reason, the concept of a "light year" seems flawed.

How can a light year be a particular value, when two people will have a very slightly different idea of exactly how long a year is?