Ask a physicist anything.

[Chesterton]

Enjoy your holiday . When I move to the States, first thing I'm gonna do is gorge myself on turkey!

Nope, sorry. You have to have Someone to give thanks to. You'll be more than welcome to celebrate our Independence Day though.

 

[Wiccan_Child]

Just another quick question...
What are your thoughts, as a physicist, about LaTeX?
The typesetting language that is. Not the rubbery material.

I've never used it myself. I did some programming in C++, that was interesting...

 

[Cabal]

That's more general, but I implicitly chose the principle argument . Generalising further, e[sup]iθ[/sup] = cos(θ) + isin(θ), but then the identity loses its elegance somewhat .

If I could be bothered, I'd escalate this further by writing the above in Taylor series expansions

But it's lunchtime, and I'm lazy

 

[Wiccan_Child]

Nope, sorry. You have to have Someone to give thanks to.

And I do. I can be thankful to my family and friends. Far be it from me to tell you how to celebrate your own holiday, but isn't the point to be thankful? Not to a particular person or deity?

You'll be more than welcome to celebrate our Independence Day though.

Oh don't you worry, one day Britain will rule the Americas once again .

 

[gipsy]

I'd have one question about gravity:

As far as I understand it, there are more or less two theories describing how gravity is "transmitted" between two masses:

1. the postulated, but till today not found, graviton or
2. a distortion of spacetime

With (1) I could "live" although I can't understand how such an important, wide reaching and "mighty" particle can't be found.

But with (2) I have the following problem:
This distortion or curvature of spacetime is often pictured as a membrane with one or more masses pressing on it and forming the curvings. While I understand that this is only a primitive analogy for us mere humans, I still don't understand what makes up this "membrane" of spacetime. If the anaogy is somehow correct, there has to be some sort of medium to propagate the pressure of the masses?!

Is there any explanation available for this, which could be understandable without a special degree in quantum physics or relativity?

 

[Chesterton]

And I do. I can be thankful to my family and friends. Far be it from me to tell you how to celebrate your own holiday, but isn't the point to be thankful? Not to a particular person or deity?

Wiki say: "Thanksgiving was historically a religious observation to give thanks to God, but is now primarily identified as a secular holiday."

I suppose one can be thankful for luck, but, by definition, there's nothing to thank for it - it's dumb luck.

Oh don't you worry, one day Britain will rule the Americas once again .

Ah, well, you couldn't do much worse ruling us than our elected officials are.

 

[Cabal]

I'd have one question about gravity:

As far as I understand it, there are more or less two theories describing how gravity is "transmitted" between two masses:

1. the postulated, but till today not found, graviton or
2. a distortion of spacetime

With (1) I could "live" although I can't understand how such an important, wide reaching and "mighty" particle can't be found.

Well, out of the four fundamental forces, gravity is the weakest - also, force particles aren't necessarily always tangible. With electromagnetic force interactions, sometimes "virtual" photons occur to transfer momentum etc, but they wouldn't be visible as light in the sense that we would describe it. So it's not quite the case that there are detectable gravity particles flying around everywhere and we just haven't seen them, many of the particles involved in force interactions simply aren't detectable.

"Particle" is often used as a term to describe chunks of interaction, for want of a better description, they aren't always solid hunks of stuff we can detect. E.g. when treating crystals quantum mechanically, it turns out you can describe the vibration of the atoms (minus any mobile electrons they may have) using a "particle" called a phonon. It's essentially a discretised sound wave in the crystal, it can't exist outside of the crystal, but it still can effectively be treated as a particle, as opposed to viewing the sound wave as being a continuous thing.

The other big problem is that for electromagnetic, strong and weak nuclear forces, we know how to treat them quantum mechanically with theories like quantum electrodynamics and quantum chromodynamics. The big problem for gravity is we don't yet have a theory of quantum gravity - one that allows us to have a quantised gravitational field and thus a force-carrying particle while still allowing general relativity to function in full as we've always known it to. So this is a big obstacle to overcome on the theoretical front.

But with (2) I have the following problem:
This distortion or curvature of spacetime is often pictured as a membrane with one or more masses pressing on it and forming the curvings. While I understand that this is only a primitive analogy for us mere humans, I still don't understand what makes up this "membrane" of spacetime. If the anaogy is somehow correct, there has to be some sort of medium to propagate the pressure of the masses?!

Is there any explanation available for this, which could be understandable without a special degree in quantum physics or relativity?

Yes, technically one can think of spacetime as a medium that reacts to mass. The vacuum isn't "nothing", it has a finite and well defined tendency to admit electromagnetic fields and radiation to propagate, it also has a zero point energy on a quantum mechanical scale. I'm by no means an expert on relativity but perhaps there is some kind of mass/vacuum interaction going on there....

 

[Wiccan_Child]

I'd have one question about gravity:

As far as I understand it, there are more or less two theories describing how gravity is "transmitted" between two masses:

1. the postulated, but till today not found, graviton or
2. a distortion of spacetime

With (1) I could "live" although I can't understand how such an important, wide reaching and "mighty" particle can't be found.

The general idea is that it zips to higher dimensions where it can't be found. Or it's too small.

But with (2) I have the following problem:
This distortion or curvature of spacetime is often pictured as a membrane with one or more masses pressing on it and forming the curvings. While I understand that this is only a primitive analogy for us mere humans, I still don't understand what makes up this "membrane" of spacetime. If the anaogy is somehow correct, there has to be some sort of medium to propagate the pressure of the masses?!

Yes: spacetime. It's a physical thing, though not in the sense of an actual member that holds our guts together.

Is there any explanation available for this, which could be understandable without a special degree in quantum physics or relativity?

Nah, just your bog-standard degree .

 

[Wiccan_Child]

Wiki say: "Thanksgiving was historically a religious observation to give thanks to God, but is now primarily identified as a secular holiday."

I suppose one can be thankful for luck, but, by definition, there's nothing to thank for it - it's dumb luck.

But again, one can be thankful to other humans. At least I have the comfort of knowing they exist .

Ah, well, you couldn't do much worse ruling us than our elected officials are.

But how Obama can do wrong? He's black!!!!

 

[JusSumguy]

Is AP a science organization now? Also, it's not my job to provide evidence for your assertions.

Nor do I care if you believe me. Your problem, not mine.

I added nothing to your insinuation that CO2 had prevented an ice-age. That's just idiocy, and it's a variation of the argument that global warming is good.

I didn't intimate a thing. The news did the intimation. You took it the way it was written. I put nothing into the facts of the stories, which were citing scientific research. That's the way YOU read them.

Cite your sources, please. Assertions get you nowhere.

Again, I have no need for you to believe that the stories I read are, in fact, stories that I actually read. You wanna be lazy.? Not my business. I already did the work. Passed it on, and you had a conundrum. Then decided that I was the bringer of the information rather that the passer on.

I made no assertions. I merely posed three questions, which you rode like that guy rode the bomb down in Dr. Strangelove.

If only you had a little knowledge. Your PRATTS are fairly idiotic.

That's the best you got?


-

 

[Chesterton]

But how Obama can do wrong? He's black!!!!

No comment. Back to physics.

 

[TheReasoner]

But again, one can be thankful to other humans. At least I have the comfort of knowing they exist .

No you don't.
According to Descartes the only person one can know to exist is oneself, provided one thinks
Though one could easily draw it further: Technically you don't even know you yourself exist. You assume you do, but what is existence? Can you prove that you fall within those parameters? Really? Are there NO alternative explanations? Say, you could be a virtual person in a simulation. There's no way to know for sure.
It's a pretty safe bet though.
I hope...

But how Obama can do wrong? He's black!!!!

And he's not Bush! That has to count for something!

 

[gipsy]

Well, out of the four fundamental forces, gravity is the weakest - also, force particles aren't necessarily always tangible. With electromagnetic force interactions, sometimes "virtual" photons occur to transfer momentum etc, but they wouldn't be visible as light in the sense that we would describe it. So it's not quite the case that there are detectable gravity particles flying around everywhere and we just haven't seen them, many of the particles involved in force interactions simply aren't detectable.

"Particle" is often used as a term to describe chunks of interaction, for want of a better description, they aren't always solid hunks of stuff we can detect. E.g. when treating crystals quantum mechanically, it turns out you can describe the vibration of the atoms (minus any mobile electrons they may have) using a "particle" called a phonon. It's essentially a discretised sound wave in the crystal, it can't exist outside of the crystal, but it still can effectively be treated as a particle, as opposed to viewing the sound wave as being a continuous thing.

The other big problem is that for electromagnetic, strong and weak nuclear forces, we know how to treat them quantum mechanically with theories like quantum electrodynamics and quantum chromodynamics. The big problem for gravity is we don't yet have a theory of quantum gravity - one that allows us to have a quantised gravitational field and thus a force-carrying particle while still allowing general relativity to function in full as we've always known it to. So this is a big obstacle to overcome on the theoretical front.

Thanks for your explanations. I'm reading (trying to read) the books of Anton Zeilinger (he's austrian too, so this is the nearest thing for me ), and I believe that I have a very basic "understanding" about quantum physics, or at least what it's all about and I've heard the term "virtual photon" from time to time, but there stops every understanding I have

I know that gravity is the weakest of the fundamental forces, but still it has (on the macroscopic level) the biggest effects. So if I think of a "force" transportet by any kind of particle, these "particles" should absolutely fill all of space because from the smallest atom to a mega black hole all matter should send out "gravitons", that's why I'm wondering why it's so impossible to find this beast, especially as it's effects are so clearly visible ...

I think I have to learn more about what a particle is or could be

Yes, technically one can think of spacetime as a medium that reacts to mass. The vacuum isn't "nothing", it has a finite and well defined tendency to admit electromagnetic fields and radiation to propagate, it also has a zero point energy on a quantum mechanical scale. I'm by no means an expert on relativity but perhaps there is some kind of mass/vacuum interaction going on there....

This sounds for me much more understandable

 

[gipsy]

The general idea is that it zips to higher dimensions where it can't be found. Or it's too small.

Hmm .. pretty elusive beast this graviton

Yes: spacetime. It's a physical thing, though not in the sense of an actual member that holds our guts together.

As I already said, this sounds much more plausible to me, than the little beast

Nah, just your bog-standard degree .

OK, had to google for "bog-standard" first ...

 

[Wiccan_Child]

I know that gravity is the weakest of the fundamental forces, but still it has (on the macroscopic level) the biggest effects. So if I think of a "force" transportet by any kind of particle, these "particles" should absolutely fill all of space because from the smallest atom to a mega black hole all matter should send out "gravitons", that's why I'm wondering why it's so impossible to find this beast, especially as it's effects are so clearly visible ...

Exactly, we can see the particle: gravity. When we feel the effects of gravity, we're effectively 'seeing' gravitons.

Then again, we know quarks exist, and we've never seen one alone. Some things just don't like to be seen!

 

[Wiccan_Child]

No you don't.

Oh, if you want to get epistemological, I know they exist to a reasonable degree of accuracy.

According to Descartes the only person one can know to exist is oneself, provided one thinks

I came to that conclusion myself a few years ago. Imagine my annoyance when I found out Descartes got there before me!

Though one could easily draw it further: Technically you don't even know you yourself exist. You assume you do, but what is existence? Can you prove that you fall within those parameters? Really? Are there NO alternative explanations? Say, you could be a virtual person in a simulation. There's no way to know for sure.
It's a pretty safe bet though.
I hope...

I disagree. I think Cogito, ergo sum is sufficient proof that I exist. It may not tell me anything about what I am, but I nonetheless am. Whatever I may be, I know that I exist, at the end of the day.

 

[Wiccan_Child]

As I already said, this sounds much more plausible to me, than the little beast

General relativity describes gravity as warping of the spacetime continuum. Quantum mechanically, it seems to be gravitons. And quantum mechanics is usually held to overrule general relativity...

OK, had to google for "bog-standard" first ...

It's a British term, don't go by the literal translation!

 

[TheReasoner]

Oh, if you want to get epistemological, I know they exist to a reasonable degree of accuracy.

That's better Exact answers FTW!

I came to that conclusion myself a few years ago. Imagine my annoyance when I found out Descartes got there before me!

You and me both...

I disagree. I think Cogito, ergo sum is sufficient proof that I exist. It may not tell me anything about what I am, but I nonetheless am. Whatever I may be, I know that I exist, at the end of the day.

Meh. Descartes was a jolly fellow who didn't know existencial dread. I should go back in time and teach him a lesson. Pray tell mr. physicist, could I do so?

 

[Wiccan_Child]

Meh. Descartes was a jolly fellow who didn't know existencial dread. I should go back in time and teach him a lesson. Pray tell mr. physicist, could I do so?

Sorry bub, it's a fixed event in time. Even if you went back and tried to change things, you'd only end up causing the event you're trying to prevent.

 

[gipsy]

Exactly, we can see the particle: gravity. When we feel the effects of gravity, we're effectively 'seeing' gravitons.

Then again, we know quarks exist, and we've never seen one alone. Some things just don't like to be seen!

Do we really "see" the graviton? ... I think we only see it's effect.

Of course I understand that we'll possibly never be able to see the graviton, but quarks, which we also can't see, have been observerd and evidenced in accelerators.