Ask a Physicist anything.

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Re: Ask a Physicist anything.
« Reply #30 on: January 20, 2013, 10:55:48 AM »
Why are 'puller particles' inconsistent with general relativity? All that would change is the analogy popular science books use to change it. There are deep connections between the two conceptual pictures if this is interesting to you i recommend reading the work of Kaluza and Klein who attempted, with some success, to describe electromagnetism in the same framework as general relativity.

Re: Ask a Physicist anything.
« Reply #31 on: January 20, 2013, 12:50:48 PM »
Why is ice slippery?
A combination of factors, applied pressure to melt the surface layer/ frictional heating to melt the surface layer. At lower temperatures however the phase properties of ice become quite complicated. In essence the bonds at the surface of the water are weaker, as you would imagine, and the structure of ice has a high free energy facilitating a "semi-liquid" state for these surface molecules. Basically the surface of ice is a very thin liquid and we all know liquids are slippery.

hmmm

not intending to be argumentative, but then you don't actually know "lots of science?"

what you meant to say was that there are some things in science of which you have some knowledge, and other things in science of which you are ignorant.

how easy is it for you to tell the difference?
Well being pedantic, and you do love pedantry, a "lot" is a noun defined as "A particular group, collection, or set of people or things." So I do know particular collections of science, most of them lie in physics but I also have A level Biology and Chemistry knowledge. So I do know "lots of science" and "there are some things in science of which I have some knowledge and other things in science of which I'm ignorant".

So is quite hard for me to see the difference, given they can mean the same thing.

Good morning, Physicist.

I wonder how many planets orbeting the star BD +5deg 1668.
And what  explains the anomalous spin of protons?

I don't know off the top of my head. But this paper seems to have the answers. http://www.annualreviews.org/doi/pdf/10.1146/annurev.aa.13.090175.001455

There are several ideas but at the minute none that are satisfactory. However the main issue with the proton spin crisis is due to its measurement. A quantum mechanical objects properties only exist within the limitations that the observation allows it to. A better measurement system needs to be constructed before we can start to determine the scale of the "anomaly". How much do you know / want to know? Are you an interested in science or did you just google "unsolved physics problems"? There are several papers I could link you to and I could help explain anything you had issues understanding.

Isn't there a couple of issues though that we are glossing over?  Roundy knows the answers to the questions that he is asking.  The gravitron is as of now just a hypothetical particle that corresponds to the gravitational force.  This however contradicts Einstien's theory that gravity is not a force, that it is the bending of spacetime.  This is why time, something without even hypothetical particles, could be effected by it.  But I obviously don't have to explain to you that relativity and quantum mechanics are not unified, and currently don't even play well together.

Now of course I could be wrong.  I have not taken a Quantum mechanics course, and I have never taken a math based Physics course.  However If you spend a large amount of time in Astro courses like I do, then you pick up the general issues regarding the two competeing theories.

Science currently does not have a great explanation for gravity, some even hypthesize that M theory would allow for gravity to be a force that is leaking in from the 11th dimension, also known as a parrallel universe.  This would explain why it is such a comparitvly weak force.

Really Roundy is just waiting for you to admit that like all scientists you don't really understand what is going on, and that you have no evidence for the puller particle that you described, except to say that the other forces have particles that correspond to them.  And even if there is a puller particle, it is at this point incompatible with the idea that gravity is not a force, but rather the curvature of spacetime. 

Now Like I said earlier, I could be butchering all of this.  But If i am, please explain what I am getting wrong, I love to learn more.
You are not butchering anything. You are right there is no unified theory between relativity and QED but that doesn't mean that they disprove each other. If you have very strong evidence for the first theory and very strong evidence for the second theory then the inability to figure out the maths connecting the two doesn't affect the strength of the evidence, just suggests an inability to do the maths.

Also what Bowler said. Treating something as "not a force" doesn't stop it being a force in the layman sense. Just affects the mathematical construct.

Re: Ask a Physicist anything.
« Reply #32 on: January 20, 2013, 01:20:48 PM »
Here's a question: if Dark Matter is supposed to make up so much of the universe and have such a mahoosive effect on galaxies, why does it appear to be impossible to detect? Surely the same property that reveals its influence on galaxies (its enormous gravity) could be used to detect it around us? And why does the dark matter theory take precedence in the scientific community over the variable strength gravity theory?
Also, why are physicists so useless at explaining the Uncertainty Principle to laymen?
Until a couple of years ago the higgs boson was impossible to detect and it is the source of all the mass in the universe. Why does effect have to be proportional to ease of detection? Dark matter is matter that doesn't emit or absorb enough light for us to be able to detect it. Gravity is a force and forces can only be detected in one of the two methods, directly by their exchange particles (hard) or by how they affect other bodies (easier). We used the latter to detect the dark matter already. If you want further proof then you would need to use the former and individual gravitons have incredibly small cross-sections, i.e they don't interact alot.

I don't think we are useless at all, I have explained it to alot of my friends. It is just that like everything else in physics if you want the FULL explanation you need to use maths and that is when laymen stop listening.

is the uncertainty not just the commutator of the two operators?
Yep it is if you use Matrices to prove it. But thats a very opaque description to most :P

Re: Ask a Physicist anything.
« Reply #33 on: January 20, 2013, 01:35:08 PM »
Most physicists, and indeed most scientists, are completely incapable of putting their thoughts down on paper. Also, since they are usually talking about these things with their peers they forget how to talk about them to other people. This is also why it takes training and practice to read a scientific paper. It's less that the subject is so complicated and more that the writer can't write clearly.
I don't agree with that. It is just that the most efficient/succinct way to convey information between fellow scientists is to use the jargon and assume base knowledge. Explaining from laymen terms upwards takes alot of time and isn't required when 90% of people reading the papers don't need that level of explanation. Papers are written for scientists.

Now popular science articles, they are written to explain physics to laymen. Courses are taught, to explain physics to laymen. If you are so interested in physics that you want to know more than popular science can explain then take a course. Because it will take that level of commitment to explain to you. You can't expect to obtain detailed knowledge without putting the work in. 

Re: Ask a Physicist anything.
« Reply #34 on: January 20, 2013, 01:43:59 PM »
hmmm

not intending to be argumentative, but then you don't actually know "lots of science?"

what you meant to say was that there are some things in science of which you have some knowledge, and other things in science of which you are ignorant.

how easy is it for you to tell the difference?
Well being pedantic, and you do love pedantry, a "lot" is a noun defined as "A particular group, collection, or set of people or things." So I do know particular collections of science, most of them lie in physics but I also have A level Biology and Chemistry knowledge. So I do know "lots of science" and "there are some things in science of which I have some knowledge and other things in science of which I'm ignorant".

So is quite hard for me to see the difference, given they can mean the same thing.

the pedantry framed a serious question, eireannach, and your answer is informative. can i point out that "lots" also means ". . . a considerable quantity or extent," in many usages? i was curious as to whether "lots" meant "a useful amount," or "a very large amount," in your own self-assessment.

one of the problems with educated people in the sciences is that they sometimes forget that because they have a command of one subject, they don't necessarily know diddly-squat about another. for instance, i know "lots" about the paleobiology and stratigraphy of metacopine ostracodes from the silurian of the baltic sea, but i'm completely ignorant of the physics of gravitation. so i'm careful to try to distinguish between what i know and what i don't.

by the way, i don't know why salt water salmon swim into freshwater to breed. when i do, i'll be able to answer the question as to why freshwater eels swim into the sea to breed, rather than staying in the lakes and streams.
true wisdom is always concise

Re: Ask a Physicist anything.
« Reply #35 on: January 20, 2013, 01:46:41 PM »
An interesting point. I think there's an element of truth in both sides. Scientists often do get into their own jargon but then so do most other disciplines; law seems to be conducted almost entirely in latin at times. They also can be poor at explaining things to non-scientists, particularly physicists. This is partly because formal physics is essentially entirely mathematical in nature and scientists often feel dishonest using poor analogies - this is why good 'science communicators' are in such demand. For example I was going to comment on my commutator comment by saying that I never found the matrix formulation particularly intuitive except for looking at commutation. Not a point will make much sense to a non-physicst but I'm not sure how to make that more accessible.

That said scientific papers are not a good example of this as they are written for scientists. The 'literature' is one place that scientists can write in a way that communicates a point efficiently and effectively but probably only to other people in the field. That said some journals strict adherence to the past passive voice does annoy me. That said when I review papers I don't tend to worry about that so long as it's readable and I'm far from alone in that.

Re: Ask a Physicist anything.
« Reply #36 on: January 20, 2013, 01:48:33 PM »
hmmm

not intending to be argumentative, but then you don't actually know "lots of science?"

what you meant to say was that there are some things in science of which you have some knowledge, and other things in science of which you are ignorant.

how easy is it for you to tell the difference?
Well being pedantic, and you do love pedantry, a "lot" is a noun defined as "A particular group, collection, or set of people or things." So I do know particular collections of science, most of them lie in physics but I also have A level Biology and Chemistry knowledge. So I do know "lots of science" and "there are some things in science of which I have some knowledge and other things in science of which I'm ignorant".

So is quite hard for me to see the difference, given they can mean the same thing.

the pedantry framed a serious question, eireannach, and your answer is informative. can i point out that "lots" also means ". . . a considerable quantity or extent," in many usages? i was curious as to whether "lots" meant "a useful amount," or "a very large amount," in your own self-assessment.

one of the problems with educated people in the sciences is that they sometimes forget that because they have a command of one subject, they don't necessarily know diddly-squat about another. for instance, i know "lots" about the paleobiology and stratigraphy of metacopine ostracodes from the silurian of the baltic sea, but i'm completely ignorant of the physics of gravitation. so i'm careful to try to distinguish between what i know and what i don't.

by the way, i don't know why salt water salmon swim into freshwater to breed. when i do, i'll be able to answer the question as to why freshwater eels swim into the sea to breed, rather than staying in the lakes and streams.

Couldn't agree more http://xkcd.com/793/

Re: Ask a Physicist anything.
« Reply #37 on: January 20, 2013, 01:53:18 PM »
I'm trying to model a non-Newtonian liquid using a hydrodynamic solver (It's a weird foam that has unique properties under shock).

Can you tell me which solver to use along with the correct equation of state/states?

Re: Ask a Physicist anything.
« Reply #38 on: January 20, 2013, 02:00:10 PM »
Eirrannach you neglected to answer my question regarding the precedence of DM theory over VG theory.
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Re: Ask a Physicist anything.
« Reply #39 on: January 20, 2013, 02:12:59 PM »
Can a 150 ft wall of ice hold back the oceans?

Re: Ask a Physicist anything.
« Reply #40 on: January 20, 2013, 03:10:58 PM »
Couldn't agree more http://xkcd.com/793/

i don't want to pick on physicists, though. biologists are guilty of it all the time.
true wisdom is always concise

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Re: Ask a Physicist anything.
« Reply #41 on: January 20, 2013, 03:52:41 PM »
Can a 150 ft wall of ice hold back the oceans?

I did the math on that a while back. Not taking into account differences in pressure, the ice wall would have to be about half a mile thick to hold back the weight of the world's oceans.

Re: Ask a Physicist anything.
« Reply #42 on: January 21, 2013, 09:46:03 AM »
Quote
Eirrannach you neglected to answer my question regarding the precedence of DM theory over VG theory.
VG theory as in MoND? If so, it has been shown that MoND does not work for at all for some systems, and its relativistic version, TeVeS, doesn't do any better.

Re: Ask a Physicist anything.
« Reply #43 on: January 25, 2013, 12:03:49 PM »
I saw the word "science" being used here in plural form as if different "sciences" exist.
For me it is nonsense.

That's my statement:
The only science is what laymen call Physics (and Mathematics is its' tool).
All other disciplines are either not a science at all or a mis-interpreted facet of Physics (chemistry is good example).
If a discipline is Science - it has Physics under the hood (you cannot make serious progress in disciplines' field without good knowledge of Physics).
So what? - the Ultimate Argument in any debate.

Re: Ask a Physicist anything.
« Reply #44 on: January 25, 2013, 01:01:29 PM »
I saw the word "science" being used here in plural form as if different "sciences" exist.
For me it is nonsense.

That's my statement:
The only science is what laymen call Physics (and Mathematics is its' tool).
All other disciplines are either not a science at all or a mis-interpreted facet of Physics (chemistry is good example).
If a discipline is Science - it has Physics under the hood (you cannot make serious progress in disciplines' field without good knowledge of Physics).

The issue is semantic. Some people choose to organize science into more specific categories, calling each one a "science".

Re: Ask a Physicist anything.
« Reply #45 on: February 23, 2013, 11:34:58 PM »

The proper way to explain gravity is using general relativity and space-time jargon that without alot of maths, just confuses people and has to be taken for granted. So instead I am going to try a quantum approach.


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If you can't explain it to a six year old, you don't understand it yourself.

Plus, you're a student, you're not a physicist until someone is paying you to do physics.  Right now you're paying to research.
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Re: Ask a Physicist anything.
« Reply #46 on: February 24, 2013, 08:50:30 AM »
"Physicist" is just another word for an engineer that doesn't do anything useful.

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Re: Ask a Physicist anything.
« Reply #47 on: March 02, 2013, 07:25:53 PM »
Quote
why do salmon swim out of the ocean into little creeks to breed?

if they started out as freshwater fish, why didn't they stay there?

if they adapted osmotically to salt water as adults, why not breed in salt water as well?

Freshwater environment is much saver for the young fish than the ocean. The old salmons breed upriver so that their children can spend their early life comfortably swimming down river, until they get stronger.
On the other hand saltwater environment is richer in recourses for the adult fish. That's why. Lampreys do the same, I don't know who else.

Re: Ask a Physicist anything.
« Reply #48 on: March 03, 2013, 12:33:03 PM »
well, then that brings up the eels, doesn't it?

then why do eels spawn in salt water, and migrate into fresh water for the duration of their life cycle?
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Re: Ask a Physicist anything.
« Reply #49 on: March 03, 2013, 10:51:37 PM »
I tried to find that out for you. My only purpose here on earth is to help mankind in their struggle for knowledge.
 
Most migrating fish live in saltwater and stay in saltwater, that means migrate to other saltwater regions due to seasonal changes in the abundance of food. Some like the ones mentioned above live in saltwater and breed in freshwater. Fish living in freshwater but breeding in saltwater seem to be rare. In fact I couldn't find another example beside freshwater eels. What advantage they have from this behaviour is currently unknown.

Re: Ask a Physicist anything.
« Reply #50 on: March 04, 2013, 08:41:14 AM »
perhaps the behavior offers no biological advantage, and is simply a historical novelty that reflects a quirk of geography in their evolutionary past.

i recall a particular sea turtle (green, i think) that tends to live in a certain part of the atlantic but travels a great distance to mauritius to breed, in spite of the fact that there are closer and more suitable islands. it's been speculated that the choice of breeding site pre-dates the opening of the midatlantic ridge, and that originally the journey wasn't so long. can't remember the details, though, so i can't vouch for the accuracy.
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Re: Ask a Physicist anything.
« Reply #51 on: March 04, 2013, 09:37:54 AM »
But if these migrations wouldn't be good for anything, evolution had long stopped them. Selection would have favoured non migrating mutations and the species would have become stationary millions of years ago. If you believe in evolution. Nothing is certain on this site.

Where has the phycisist gone? I've got some questions!

Re: Ask a Physicist anything.
« Reply #52 on: March 04, 2013, 09:50:36 AM »
But if these migrations wouldn't be good for anything, evolution had long stopped them. Selection would have favoured non migrating mutations and the species would have become stationary millions of years ago. If you believe in evolution. Nothing is certain on this site.


so everything that exists has to be adaptive, because if it wasn't adaptive, it wouldn't exist, and everything that exists has to be adaptive?

there's a circle in here, martian.

there's lots of biogeography that's based on simple chance.

why aren't there marsupials in norway?
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Re: Ask a Physicist anything.
« Reply #53 on: March 04, 2013, 10:41:30 AM »
But if these migrations wouldn't be good for anything, evolution had long stopped them. Selection would have favoured non migrating mutations and the species would have become stationary millions of years ago. If you believe in evolution. Nothing is certain on this site.



so everything that exists has to be adaptive, because if it wasn't adaptive, it wouldn't exist, and everything that exists has to be adaptive?

there's a circle in here, martian.

there's lots of biogeography that's based on simple chance.

why aren't there marsupials in norway?


You're just teasing now, right?
« Last Edit: March 04, 2013, 10:43:11 AM by Homesick Martian »

Re: Ask a Physicist anything.
« Reply #54 on: March 04, 2013, 11:25:22 AM »
not on your life, my friend.

marsupials or their fossils are found in the neotropics, australasia, and antarctica. one has invaded north america within the last 100 years or so. the fact that they don't occur in norway is probably a historical accident, and likely doesn't have anything to do with their evolutionary fitness to live there.

and the fact that freshwater fish rarely breed in salt water may be no more an adaptive response to physiology than the green sea turtles breeding on the mauritius beaches.

hence my question for the physicist. i'm curious about eels, and i have never heard an answer to the question.
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Re: Ask a Physicist anything.
« Reply #55 on: March 04, 2013, 11:51:40 AM »
Of course much is accidental. It's accidental that we have two hands but not four. But it's not accidental that we have hands at all and not celeries like Scuzzlebutt. Hands are useful, celeries are not. That's why we developed, but Scuzzlebutt didn't.

In like manner it's by accident that there are no marsupials in Norway and that your turtles breed in Mauritius. But that they travel that distance at all must be useful. Otherwise they wouldn't. The genes responsible for that behaviour would have simply died out.

That may be a circle but it's the circle of life, buddy.
« Last Edit: March 04, 2013, 12:03:09 PM by Homesick Martian »

Re: Ask a Physicist anything.
« Reply #56 on: March 04, 2013, 12:09:02 PM »
In like manner it's by accident that there are no marsupials in Norway and that your turtels breed in Mauritius. But that they travel that distance at all must be useful. Otherwise they wouldn't. The genes responsible for that behaviour would have simply died out.

not necessarily, and the idea is very interesting.

in one scenario, there's no necessity that swimming to mauritus need be useful, merely that it be less harmful than the alternatives. if all the other options to a turtle are less adaptive, then evolution would favor the least harmful strategy, not the most helpful one.

in a second scenario, if all the options are equally neutral, then evolution would have no reason to favor one over another. perhaps there is no advantage to swimming to mauritius, if energetically it is within a neutral region for adaptive fitness. turtles have to swim somewhere, after all, and perhaps mauritius is no farther away than swimming in endless circles around anywhere else. so swimming there comes at no cost, and is free to be influenced by history and not by evolution.

not everything that exists is required to be adaptive. to say that it does is where the circular reasoning of adaption comes in. that's a logical flaw that often crops up in discussions of evolution.
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Re: Ask a Physicist anything.
« Reply #57 on: March 04, 2013, 07:32:48 PM »
Sorry that doesn't make sense to me. As I conceive it, evolution, like human society, is governed by economy. Thats why animals living in caves will lose their eyes by time. They are not harmful to them, but they are of no use. Why put energy in something which has no use? The "least harmful" strategy is allways the one that costs less. Why do turtles have to "swim somewhere"? They could stay where they are. That would be the "neutral" strategy. When they leave the "neutral" strategy there must be a profit for them. Every material life is governed by the finity of energy available. No matter if you are a little worm or the leader of a nation, essentially we're all in the same business.

Re: Ask a Physicist anything.
« Reply #58 on: March 05, 2013, 07:00:42 PM »
are you familiar with the concept of adaptive landscapes, martian?



the most economical strategy may not be accessible to an organism because reaching the fitness peak requires crossing a maladaptive valley. evolution looks for a local optimum, not ultimate optima, and so sometimes what persists is not governed by economy as we see it, but by history. things that are quite expensive persist over a long time because changing to a more economical pattern is more expensive than staying where you are.

turtles swim for the same reasons birds migrate-- there are advantages to being in different places at different times. there's no reason to assume that what is the best environment for a slow -moving vulnerable baby turtle is also the best for a 500 kg pelagic adult.
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Re: Ask a Physicist anything.
« Reply #59 on: March 05, 2013, 10:23:01 PM »
Quote
there are advantages to being in different places at different times.

yeah, could be that this is advantage enough to keep them roaming. Nice diagram, have nothing to argue against.