http://www.physicsforums.com/blog.php Scientific physics forums for professionals and students to discuss serious issues and topics regarding physics in theory, practice, study and reality. Students can also find help for homework and career perspectives en Wed, 16 May 2012 22:18:00 GMT vBulletin 60 http://www.physicsforums.com/Nexus/misc/rss.jpg http://www.physicsforums.com/blog.php http://www.physicsforums.com/blog.php?b=3963 Wed, 16 May 2012 21:01:38 GMT Dalespam recently brought up an interesting semantic issue. What is the meaning of “*relative*” versus “*absolute*”? I did not have time to intervene in that thread but the subject links well with... Dalespam recently brought up an interesting semantic issue. What is the meaning of “relative” versus “absolute”? I did not have time to intervene in that thread but the subject links well with the musings of this Blog.

Obviously “relative” is what is defined “in relation with” or by comparison with another object, but in the context of Special Relativity this may mean three different things:

(a) That a measurement (of time or space) is made from and hence with regard to a reference frame. This must forcefully happen. The way to measure in an absolute manner does not exist. In this sense, all measurements are relative.

(b) That the outcome of a measurement is affected by the fact that it is made from a reference frame and hence different from frame to frame, that is to say, frame-dependent. This does not always happen. In pre-SR physics, it was admitted that the measurement of the distance travelled by a projectile in a time lapse was frame-dependent but it was also expected that the measurement of the length of an object and of time elements (duration, simultaneity) would be absolute, i.e., frame-independent. In SR, instead, all time and space measurements have been proved to be frame-dependent but they are so in a manner that they make the measurement of the speed of light frame-independent, absolute in this second sense.

(c) That a measurement from a given reference frame is worse than one effected from another frame, which is better, insofar as the former provides less information than the latter.

This is also a common meaning in day-to-day language. A book by Balzac which impressed me many years ago was called À la recherché de l’absolu. The protagonist was a chemist that sought the ultimate and highest discovery and wasted his fortune and his life in that vain attempt. We also talk in this sense about absolute love, the one whose qualities and intensity would make all other emotions look pale and empty… Finally, in the political arena, we use the concept of absolute power, the one that is over-comprehensive and is not balanced by any constraints.

Shifting back to SR, the point of previous posts has been that the aim of the game, when one handles kinematic concepts, is solving problems about causality. Thus an absolute measurement would be one that provided the completest level of information in this respect. In particular, since the problem is “can event A have an influence on event B?”, the absolute answer would be “yes or no, no matter how fast the agent carrying the causal influence may travel, even if it travels at infinite velocity, that is to say, instantaneously”.

In pre-SR physics, it was initially thought that the measurement of simultaneity [in sense b) = all frames get the same value] would also provide that optimal degree of information, in sense c) (such value furnishes knowledge about the causality ability of infinitely fast agents).

Given this, when it was discovered that “light does not take the motion of the source”, it was then thought that a measurement made with a light signal could not achieve that aim; scientists thus assumed that the absolute knowledge would only be possible in a particular frame, the aether frame, the aether being a (non-material…) medium where light would propagate as a disturbance, just like sound does in the air.

However, it was left open the question as to whether a measurement other than with light, being invariant (in as much as time is concerned) in sense b), would still provide full information in sense c). This would enable us to measure what sometimes is called the absolute velocity of light, which is thus named because it would be made out of absolute time measurements, although such velocity would be relative in sense b), since it would forcefully be frame-variant...

At this juncture, I leave aside the thorny issue of the “relative” merits of Lorentz, Poincaré and Einstein. What seems clear for everybody today is that absolute time is not measurable. The only real time is the relative one in sense b) (it is frame-variant) and…

also in sense c) (it does not provide full information). Or not? What do you think? Do you believe that you could have it both ways? Variant measurements [relative in sense b] that are each of them absolute [in sense c), meaning that each of them leads to a different version about what happens and what does not happen in causality terms]…?

Well, that is what some authors suggest, those authors who argue that “faster-than-light travel and time travel” are necessary companions. ]]> Saw http://www.physicsforums.com/blog.php?b=3963 http://www.physicsforums.com/blog.php?b=3924 Mon, 30 Apr 2012 12:16:54 GMT This autumn, I will be enrolled as a freshmen for my first semester at a large, public research university. Despite still being in high school, I feel that I am almost as prepared as ever to make... This autumn, I will be enrolled as a freshmen for my first semester at a large, public research university. Despite still being in high school, I feel that I am almost as prepared as ever to make contrabutions to mathematics and physics (Specificially, my main interest is the application of symplectic geometry to quantum mechanics. I have other interests such as quantum computing, ergodic theory, Bohmian mechanics, and mathematical music theory.)

However, I know very little about, and admittingly frightened of the prospect of, the research and publication process. Also, I probably need some (or a lot of) help in the form of collaboration. Therefore, I am planning to email some of my prospective professors/research advisors/collaboraters whose research fields have sufficient overlap with my interests.

Since this would be my first time interacting with these very important people, I would like to make a good first impression. I hope I don't screw up. ]]> Snicker http://www.physicsforums.com/blog.php?b=3924 http://www.physicsforums.com/blog.php?b=3923 Sat, 28 Apr 2012 14:53:01 GMT Our heart aches to know that some children are brought to this world just to die by bombs while playing outside with some friends. If I were god, would I run out of tears? For he is, he could not. Our heart aches to know that some children are brought to this world just to die by bombs while playing outside with some friends. If I were god, would I run out of tears? For he is, he could not. ]]> Leong http://www.physicsforums.com/blog.php?b=3923 http://www.physicsforums.com/blog.php?b=3916 Tue, 24 Apr 2012 15:34:48 GMT I am Amrit Kafle from Nepal. I am seeking admission to graduate level in physics in university of USA. My TOEFL score is 81 and GRE score is 1210. I want to enroll my name in university as a... I am Amrit Kafle from Nepal. I am seeking admission to graduate level in physics in university of USA. My TOEFL score is 81 and GRE score is 1210. I want to enroll my name in university as a graduate student in physics with possible financial support.

First of all, I am going to write about my personal background. I am from a lower class family. My family was struggling even to earn hand to mouth when I was growing up. I completed my primary and secondary level from a village school with hardship and great effort. After completing my secondary level, I took admission in undergraduate level in science stream though I had to suffer a great physical and economical trouble. I took me one hour to reach my college on the bicycle from my village. I could not have enough money to buy Tiffin. After 12 hours I used to reach home and then I could get an opportunity to have the food prepared by my mother. I still remembered that my English teacher had offered a jacket on seeing me shivering with cold in her class. It seems to be an exaggerated story but it is my reality in which I had to undergo. I completed my undergraduate level thinking that I would change my dream into reality. At that time, my inclination towards science was not clear. I only wanted to study science because I had thought that science subject could reveal all secrets of nature and to study science is exciting and challenging. I could not continue my further study immediately due to economical crisis in my family. After one year I managed to study B. S. in a college at Janakpur. During three years at Janakpur, I managed to live and study with a little financial support from my family and a small earning from private tutorial classes. I came to Kathmandu in order to continue my further study in master level. The college education became possible because of my hard-work as a part time tutor. I worked 10 hours a day in the expensive capital city, Kathmandu. Nowadays I am teaching physics to undergraduate level in an institution.
With regards to my academics, it is not satisfactory. I am confident that I have enough talent and potential to pursue higher study as a graduate student at any university. Under the circumstances what qualification I have earned, I could not convince myself that I should give up my attempt to continue my study in physics. I had not given my hundred percent effort to my study. Neither in secondary level nor in undergraduate level, did I well. I had to work hard to earn my living and continue my study simultaneously. If I were given opportunity to study only, I surely would have better academic records. I have a keen interest in physics. I could feel pleasure when I thought myself as a physics student involving in research. Therefore I continued my study in physics in spite of biter and difficult circumstances. I want to serve mankind being a good researcher of theoretical physics.
I am well interested in Nuclear physics, especially nuclear fission, nuclear fusion and radioactive decay. I would study and carry on a research in particle physics too. I want to increase my knowledge regarding the quark theory and electromagnetic structure of nucleons. Next area of my interest is high energy process and nucleosynthesis.
I have chosen This University because it is providing excellent education with internationally respected faculty. It has a greater opportunity for the research in theoretical and experimental physics. I am very interested to pursue my career in research. I have strong desire to be a graduate level student in esteemed and reputed university. Please suggest the best way that can lead me to achieve my aim by being a good student of physics . Thanking alot ]]> Bhabesh http://www.physicsforums.com/blog.php?b=3916 http://www.physicsforums.com/blog.php?b=3913 Tue, 24 Apr 2012 05:01:23 GMT Hi!! I am visited physics forum first time and realized its worthy. so joined it but still I am unaware to it so i hope be familiar to it very soon. thank you forum and members!! Hi!!
I am visited physics forum first time and realized its worthy. so joined it but still I am unaware to it so i hope be familiar to it very soon.
thank you forum and members!! ]]> avinashthube http://www.physicsforums.com/blog.php?b=3913 http://www.physicsforums.com/blog.php?b=3903 Mon, 16 Apr 2012 07:29:29 GMT Hi, Will you be so kind to help me with my studying (it is not a homework) and give me a definition of the following (some of the following) words. There are some sentences, but I need the... Hi,

Will you be so kind to help me with my studying (it is not a homework) and give me a definition of the following (some of the following) words. There are some sentences, but I need the definition of the words in bold, not of the whole sentence.

It will be very nice if you write also in what field of science the given definition is used.

1) Controlled orientation
2) Heteronanotube
3) decomposition
4) superlattice
5) acceptor
6) Co-SiO2 was found to be the best catalyst/support combination for the preparation of MWNTs, but most of the other combinations led to carbon filaments, sometimes covered with amorphouslike carbon.
7) donor
8) indenter
9) It accounts for the rapid coagulation of hydrophobic particles in water and may also account for the rapid folding of proteins.
10) clathrate
11) ball mill
12) wet chemical methods
13) This question has been widely studied worldwide and the general approach is the addition of a surfactant in order to stabilize the CNT in the liquid.
14) gene delivery
15) a probe
16) matrix isolation
17) molecular motors, biological motors
18) chelate



I thank you in advance :) ]]> Domka http://www.physicsforums.com/blog.php?b=3903 http://www.physicsforums.com/blog.php?b=3900 Thu, 12 Apr 2012 20:22:43 GMT A lot of people ask about the X-Zylo and there is a small inexpensive book on Amazon about the physics of the flight dynamics from a debate among MIT grad students in Aero/Astro. I think it says it... A lot of people ask about the X-Zylo and there is a small inexpensive book on Amazon about the physics of the flight dynamics from a debate among MIT grad students in Aero/Astro. I think it says it performs basically like an infinite lift surface because of the cylinder and rotation. They tested modifications too. ]]> x-zylo fan http://www.physicsforums.com/blog.php?b=3900 http://www.physicsforums.com/blog.php?b=3897 Tue, 10 Apr 2012 06:22:41 GMT I've made my first friend (hopefully). "PKruse" you have been most helpful in answering questions i have, thank you so much, and i hope when I enter college you will still be here answering my questions with candor, knowledgeable replies. ]]> AKwolfeEng http://www.physicsforums.com/blog.php?b=3897 http://www.physicsforums.com/blog.php?b=3896 Mon, 09 Apr 2012 01:13:53 GMT some grammar check, word choice, make sound better. thank youuu!! 300 word limit.

Dear Editor,

Re the March 20th article, "New Nutritional Labels for Meat Help You Make Smarter Choices." I am writing to express my enthusiasm and respects at the new rule of the "Department of Agriculture on meat labeling." Such labeling is necessary to provide consumers clear and non-misleading information regarding the nutritional content on ground meat and poultry.

As an aspiring Nutritionist's food diary, I am appalled that the USDA has taken a toll in 2012 by finally enforcing labels on just about the most common cuts of meats. If food labels appear on cereals, bread, yogurts, drinks and all kinds of other products why are meats and poultry excluded from this privilege? With the numerously foods currently being genetically modified individuals can be more accountable of what they are consuming and can make informed decisions on their intake. So one can see how much one is eating, stick to their diets and guidelines, not to mention every parent wants to know what they are feeding their kids. In addition food markets should provide consumers with enough nutritional information at the store to choose what to eat or not. Enabling individuals in making their own “healthy” meat choices at their own risk and more accountable about their health outcomes, but with their own consent.
As the rates of obesity and deaths keep increasing in the united states, just how the editor states a "New study made headlines earlier this month with its finding that a diet heavy in red meat increases chances of dying from a chronic disease by 12 percent." Americans need to be more aware of their health. If your health is compromised, nutritional information may be crucial to your well-being and even helping to manage weight loss. People need to start educating themselves and be on the lookout for what they put in their bodies. You are what you eat! ]]> goshclaudiaaa http://www.physicsforums.com/blog.php?b=3896 http://www.physicsforums.com/blog.php?b=3893 Sun, 08 Apr 2012 06:36:13 GMT Well i'm beginning to understand that these moderators are in no way shape or form allow me to post career help blog or threads. All well, i'm still amazed at the rapid response i'm getting from the forums. ]]> AKwolfeEng http://www.physicsforums.com/blog.php?b=3893 http://www.physicsforums.com/blog.php?b=3889 Sat, 07 Apr 2012 05:30:14 GMT I setup this Physics Forum profile alongside my website. I believe this is sufficient enough to show results.
I got a panthlet today from UW, the university i wish to attend.
I've gotten for the most part great feedback on my blog posts. ]]> AKwolfeEng http://www.physicsforums.com/blog.php?b=3889 http://www.physicsforums.com/blog.php?b=3886 Fri, 06 Apr 2012 08:25:08 GMT yukawa potential is a new theory which describe how nuclear force is action. square well nuclear potential provides the basis of quantum theory with discrete energy levels and corresponding... yukawa potential is a new theory which describe how nuclear force is action.
square well nuclear potential provides the basis of quantum theory with discrete energy levels and
corresponding bound state just like in atoms
– Presence of nuclear quantum states have been confirmed
through
• Scattering experiments
• Studies of the energies emitted in nuclear radiation
• Studies of mirror nuclei and the scatterings of
protons and neutrons demonstrate
– Without the Coulomb effects, the forces between two
neutrons, two protons or a proton and a neutron are the
same
• Nuclear force has nothing to do with electrical charge
• Protons and neutrons behave the same under the nuclear force
– Inferred as charge independence of nuclear force.
2
Nuclear Potential – Iso-spin symmetry
• Strong nuclear force is independent of the
electric charge carried by nucleons
– Concept of strong isotopic-spin symmetry.
• proton and neutron are the two different iso-spin state of
the same particle called nucleon
– In other words,
• If Coulomb effect were turned off, protons and neutrons
would be indistinguishable in their nuclear interactions
• Can you give another case just like this???
– This is analogues to the indistinguishability of spin up
and down states in the absence of a magnetic field!!
• This is called Iso-spin symmetry!!!
this modul I get from my lecture Arif Hidayat when study physics nuclear ]]> dini andriani http://www.physicsforums.com/blog.php?b=3886 http://www.physicsforums.com/blog.php?b=3885 Fri, 06 Apr 2012 04:21:34 GMT Here is Nick Herbert's version of the proof of Bell's theorem. It is, I believe, the simplest known proof of Bell, and the particular numerical example used by Herbert was in fact the one that Bell used in his talks to popular audiences.

I should say, however, that Herbert states the conclusion of his argument a bit too strongly. He claims that his reasoning implies that experiments have definitively disproven the hypothesis that reality is local. But that's not quite true, because there are various experimental loopholes. So I would rather state the conclusion in this way:

"The predictions of quantum mechanics cannot all be completely correct in a local deterministic universe." And without further ado, here is my restatement of Herbert's argument to get to that conclusion:

1. Entangled photons behave identically at identical polarizer settings.
2. The believer in local hidden variables says that the polarizer angles the photons will and won't go through are agreed upon in advanced by the two entangled photons.
3. In order for the agreed-upon instructions (to go through or not go through) at -30 and 30 to be different, either the instructions at -30 and 0 are different or the instructions at 0 and 30 are different.
4. The probability for the instructions at -30 and 30 to be different is less than or equal to the probability for the instruction at -30 and 0 to be different plus the probability for the instructions at 0 and 30 to be different.

The last statement is what is known as a Bell inequality, and it is in direct contradiction with the predictions of quantum mechanics, which in this case says that the probability for the results to be different at -30 and 30 is actually GREATER than the probability for the results to be different at -30 and 0 plus the probability for the results to be different at 0 and 30. ]]> lugita15 http://www.physicsforums.com/blog.php?b=3885 http://www.physicsforums.com/blog.php?b=3884 Fri, 06 Apr 2012 00:32:42 GMT I'm going to be hopefully starting on Linear Algebra and Differential Equations in the next three weeks, but first I want to finish my study of Electricity (another 15 hours), also do about 10 hours of Optics and review my chemistry. I self-taught myself chemistry back in Oct 2010. That was the first science book I read when I decided that I needed to learn more about science. It was a bit of a blur because it had been roughly 20 years since I had real exposure to science. This time I expect it will be much more fun and engrossing. I'm real keen to learn the properties of objects and why they have those properties. The hopefully with Quantum Mechanics I will be able to understand how they know the structure of the elements.

The biggest obstacle I have going against me is that I don't get to feel the thrill of ambition. The odds of me abandoning my writing career and becoming a physicist are extremely low. In fact I would view it as a serious failure if I abandoned my writing career. Maybe if I were to write another 5 books I would consider quitting writing because, let's be honest, most readers read only one or two books by the same author. If I had the thrill of ambition in me I could be studying this stuff thinking that there is some huge reward waiting for me down the road but that is not the case. The only reward I have is a deeper understanding which is in itself a bonus, but surely a more exciting prize would be to publish an article in a peer reviewed journal and have it widely cited. Maybe I will at least be able to review popular science books.

Another major obstacle is that I simply am not willing to get my hands dirty and go out and conduct an experiment or build something. I was trying the other day to understand a DC motor and batteries. It is all very abstract and I still don't really get it, even with the help of several youtube videos. The only way I can really understand this stuff is to go out and build a dc motor myself but that would probably take about 3 hours and maybe 30 dollars which is time and money that I would rather spend with my nose in a book. It is quite remarkable that I will have gone through a thorough study of classical and quantum mechanics without ever having stepped inside a lab or ever having done an experiment or even seen someone else do an experiment. What I'm hoping is that when I have kids, we'll do the experiments together.

I've only been studying science for a year and a half so I'm still innocent, naive and not disillusioned. With literature, on the contrary, I've studied it for 18 years and I've seen how prevalent bad taste and stupidity is in the humanities. For that reason, I'm going to try to gear my kids towards the sciences, not the humanities, but of course ultimately they're free to do what they want. (I've always been grateful that my parents never pressured me to do one thing and not something else) It's probably true that if I were to devote the next 15 years of my life to science I would probably uncover the same corruption and fraud that I've seen in the humanities, but since I don't have that experience I still view science through rose-colored glasses. ]]> bobsmith76 http://www.physicsforums.com/blog.php?b=3884 http://www.physicsforums.com/blog.php?b=3877 Sat, 31 Mar 2012 03:43:44 GMT Image: http://upload.wikimedia.org/wikipedia/commons/5/50/Albert_Einstein_%28Nobel%29.png (Image: Albert Einstein, 1921, public domain) *3D Printer with Nano Precision* (12 March 2012, Vienna...
(Image: Albert Einstein, 1921, public domain)

3D Printer with Nano Precision (12 March 2012, Vienna University of Technology)
"Printing three dimensional objects with incredibly fine details is now possible using “two-photon lithography”. With this technology, tiny structures on a nanometer scale can be fabricated."
Article: 3D-Printer with Nano-Precision (beautiful pictures+video)

Physicists Find Patterns in New State of Matter (29 March 2012)
"In a paper published in the March 29 issue of the journal Nature, the scientists describe the emergence of "spontaneous coherence," "spin textures" and "phase singularities" when excitons -- the bound pairs of electrons and holes that determine the optical properties of semiconductors and enable them to function as novel optoelectronic devices -- are cooled to near absolute zero."
Paper: Spontaneous coherence in a cold exciton gas
Article 1, Article 2

Einstein's archive now available online (29 March 2012)
(so now you can check if he really meant E=mc², or something else :smile:)
The archive is here: http://www.alberteinstein.info/
Gallery example: http://www.alberteinstein.info/gallery/gallery.html
Article

Aether
I experienced a very good aether today, the weather was really nice, and I found five books at a nice price, four physics books and one on mathematics. So I've got nothing to complain about!

I wish everybody a good weekend! :smile: ]]> DennisN http://www.physicsforums.com/blog.php?b=3877