Physics related research discussions

• Bill LaPorte-Bryan

  Is spacetime quantized or continuous?

  General Relativity assumes that spacetime is continuous. Quantum mechanics assumes that spacetime is quantized. They have both passed every experimental test and both make accurate predictions. General Relativity assumes that spacetime is continuous. Quantum mechanics assumes that spacetime is quantized. They have both passed every experimental test and both make accurate predictions. But it seems to me only one of those assumptions can be right unless there is an abrupt discontinuity at some point as one examines the characteristics of spacetime at every distance scale from the largest (the universe) to the smallest (the Planck scale). So which is it?

  Recent replies ⋅ Show All (23)

  • 
    Bill LaPorte-Bryan replied

    If I understand you, Fernando, you're saying that space-time is continuous and quantized. Is that right? I hope so, because I think space-time has to be continuous for there to be any hope ofIf I understand you, Fernando, you're saying that space-time is continuous and quantized. Is that right? I hope so, because I think space-time has to be continuous for there to be any hope of finding a theory of everything while, at the same time, it has to be quantized for quantum mechanics to make any sense. So, if it's both, it's possible that some "true physicist" will discover a theory of everything that satisfies all of the constraints that Raphael mentioned in his earlier comment.

    2 minutes ago
• Sharanya Achut

  Why do planets of the Solar system revolve around the Sun in an *elliptical*, not *circular* orbit?

  ?

  Recent replies ⋅ Show All (32)

  • 
    Nainan Varghese replied

    As my last post (May 25th) disappeared, I will repeat the same. Dear Ulrich, Even in fifteenth century AD, there was widely accepted explanation, based on biblical teachings, on movements of cosmicAs my last post (May 25th) disappeared, I will repeat the same. Dear Ulrich, Even in fifteenth century AD, there was widely accepted explanation, based on biblical teachings, on movements of cosmic bodies ‘Will of God’ was very simple and logical cause for all their observed movements. Yet, sadly many astronomers wasted lot of their time to observe and record relative positions of few bodies in solar system. On these, Kepler based his laws of planetary motions. Unfortunately, at that time, Sun was unknown to have translatory motion in space. Because of this, all planetary orbits were rightly considered as paths around the sun. Kepler’s laws on planetary motion are derived from parameters of relative positions and they are able to predict accurately all phenomena which depend on relative positions of these bodies. Using them to analyze other parameters of planetary body may not always be right. Do not belittle questions raised by Estepan on the ground that he is not a physicist. Similar questions are raised by many. Since there are no logical answers, most students fall in line with teachings of contemporary theories. All the answer academic world can provide is the advice to refer old theorems and books. Many of these contradict themselves, when considered together. I could, so far, find no books, which states that elliptical planetary orbits are apparent in nature. Every form of literature treats circular/elliptical planetary/satellite orbit as real path followed by a planetary/ satellite body. Since sun is a moving body, elliptical orbit cannot not be real path traced by a planet but as it would appear to an observer on static central body. That is why, while it takes one or two pages to describe earth’s orbital path by current laws, it takes hundreds of pages to describe moon’s orbital path by mathematical manipulations. It must be noted that although moon is the easiest cosmic body to observe from earth, it was left out during formulation of planetary laws. However, we routinely use these laws to describe moon’s orbital path as well. If you care for my opinion on three body problem, see article at http://vixra.org/abs/1205.0097 Nainan

    7 minutes ago
• Alleyrand Medeiros

  Why the neutron which has the same mass as the proton has no electric charge and the proton have?

  Is not there a relationship between the electric charge and its mass?
• Prosper Chou

  Do left-hand electromagnetic waves exist in nature? And how can we find it?

  It is well known that there are no natural materials having simultaneously negative values of the dielectric ε and the magnetic μ. In general, we call the materials left-hand Material orIt is well known that there are no natural materials having simultaneously negative values of the dielectric ε and the magnetic μ. In general, we call the materials left-hand Material or double-negative Media. But we have found some special materials in our labs. When the electromagnetic waves go though the left-hand Material by some special frequencies, the waves will be changed from right-hand to left-hand. What I want to ask is that, does a left-hand electromagnetic wave exist in nature? And how can we find it?

  Recent replies ⋅ Show All (1)

  • 
    Prosper Chou replied

    in my opinion,all the things both have the positive and the negative charactors,but maybe the god is selfish,he always showed us only one aspect of the things ,positive or negative.on the other handin my opinion,all the things both have the positive and the negative charactors,but maybe the god is selfish,he always showed us only one aspect of the things ,positive or negative.on the other hand ,we can say that our theories in physics are not integrity,there exists the parallel theories in nature .to amazing,more and more experiments in labs had shown that what i said above are right.so, I believe that there exists the left-hand electromagnetic wave in nature.theorically,we can get the answer in Maxwell equations.But,what confuses me is that how can we find its shadow?Plesase,I beg your help!!!

    7 hours ago
• Javier Chornet

  Instant transmission of mechanical information in General Relativity?

  Suposing we stretch a rope between the Earth and the Sun (for example) and we put a dynamometer in each end measuring a tension (T), when we cut the Earth's rope, when will the Sun's dynamometer stopSuposing we stretch a rope between the Earth and the Sun (for example) and we put a dynamometer in each end measuring a tension (T), when we cut the Earth's rope, when will the Sun's dynamometer stop measuring any tension?: instantly?, after 8:19 minutes?

  Recent replies ⋅ Show All (4)

  • 
    Adam Jacholkowski replied

    THis question is quite old , I remember it from times of studying SR long, long ago. This relates also to the question of existence of perfectly rigid objects in Nature.

    4 days ago
• Fernando Loup

  Warp Drive: Fact or Fiction?

  Is the Warp Drive fact or fiction? Can the Warp Drive be fact or fiction? Warp Drives are Exotic solutions of the Einstein Field Equations of General Relativity that "allows" Faster Than LightIs the Warp Drive fact or fiction? Can the Warp Drive be fact or fiction? Warp Drives are Exotic solutions of the Einstein Field Equations of General Relativity that "allows" Faster Than Light Space Travel within the framework of General Relativity Note that the word "allows" is between quotes. The first of these Exotic solutions was discovered by the Mexican mathematician Miguel Alcubierre in 1994. The second was discovered by the Portuguese mathematican Jose Natario in 2001. Alcubierre is PhD from University of Wales in Cardiff UK and Natario is PhD from University of Oxford UK. Their works are here: http://arxiv.org/abs/gr-qc/0009013 http://arxiv.org/abs/gr-qc/0110086 The Warp Drive is an entire family of solutions of the Einstein Field Equations of General Relativity like the Schwarzschild or the Reissner-Nordtstrom solutions are for Black Holes but Warp Drives, although mathematical elegant solutions faces some serious problems an excellent description about the problems Warp Drive faces can be given by http://arxiv.org/abs/gr-qc/0406083 http://arxiv.org/abs/0710.4474 I would like to discuss in ResearchGate the Warp Drive. Using the scientific works of arXiv or HAL to start to show how this theme can be interesting for people in General Relativity abstract of arXiv:0710.4474 The General Theory of Relativity has been an extremely successful theory, with a well established experimental footing, at least for weak gravitational fields. Its predictions range from the existence of black holes, gravitational radiation to the cosmological models, predicting a primordial beginning, namely the big-bang. All these solutions have been obtained by first considering a plausible distribution of matter, and through the Einstein field equation, the spacetime metric of the geometry is determined. However, one may solve the Einstein field equation in the reverse direction, namely, one first considers an interesting and exotic spacetime metric, then finds the matter source responsible for the respective geometry. In this manner, it was found that some of these solutions possess a peculiar property, namely 'exotic matter,' involving a stress-energy tensor that violates the null energy condition. These geometries also allow closed timelike curves, with the respective causality violations. These solutions are primarily useful as 'gedanken-experiments' and as a theoretician's probe of the foundations of general relativity, and include traversable wormholes and superluminal 'warp drive' spacetimes. Thus, one may be tempted to denote these geometries as 'exotic' solutions of the Einstein field equation, as they violate the energy conditions and generate closed timelike curves. In this article, in addition to extensively exploring interesting features, in particular, the physical properties and characteristics of these 'exotic spacetimes,' we also analyze other non-trivial general relativistic geometries which generate closed timelike curves.

  Recent replies ⋅ Show All (10)

  • 
    Fernando Loup replied

    http://www.dailygalaxy.com/my_weblog/2012/03/space-ships-as-death-stars-leading-space-travel-physicists-say-yes.html Long distance space travel could create the ultimate 'killer entrance',http://www.dailygalaxy.com/my_weblog/2012/03/space-ships-as-death-stars-leading-space-travel-physicists-say-yes.html Long distance space travel could create the ultimate 'killer entrance', devastating your destination and anything around the arriving spacecraft, according to calculations by Geraint Lewis and colleagues from the University of Sydney. The Alcubierre warp drive is a theoretical tool that would allow spacecraft to travel long distances in space rapidly by deforming the space-time continuum in a bubble around the spaceship. Miguel Alcubierre, a Mexican physicist, proposed this warp drive in 1994 as a way to travel faster than light, overcoming the limit on particles travelling at such speeds posed by Einstein's theory of special relativity ."When the spacecraft decelerates to stop at its destination, the particles collected at the front of the spacecraft are released with such high-energy that they would destroy anything they came in contact with. During the journey the particles picked up and included inside the bubble could threaten the safety of people travelling in the spacecraft," said Geraint Lewis of the University of Sydney School of Physics. "It sounds like it's straight from science fiction, and in a way it is, as the Alcubierre warp drive is a theoretical solution to the problem of travelling the huge distances in space in a reasonable amount of time," said Lewis. "But unlike science fiction, the Alcubierre warp drive completely obeys Einstein's general theory of relativity." "All innovations start with theory, however, so these calculations contribute to our understanding of how such speeds could be achieved. Our team decided to consider what would happen to particles and radiation that a spacecraft, travelling in a bubble created by the Alcubierre warp drive, would come across as it travelled through space," explained Lewis. "What we've shown is that when this spacecraft decelerated to arrive at its destination, it would release high energy particles which would destroy anything near the spacecraft's landing spot."While scientists have examined how it's theoretically possible to create a bubble around a spacecraft with the Alcubierre warp drive compressing space-time in front of the bubble and expanding it behind the bubble, there has been little consideration of how this high-speed bubble would interact with particles of matter and light. "Our calculations show that particles that come in contact with the warp bubble can get caught up and congregate in front of the spacecraft, and some particles even enter the warp bubble," added Lewis. "Interestingly, the energy burst released upon arriving at the destination does not have an upper limit. You can just keep on traveling for longer and longer distances and the energy that will be released will continue to increase - one of the odd effects of General Relativity," obseerved team researcher, Brendan McMonigal. "Even for very short journeys the energy released is so large that you would completely obliterate anything in front of you. It seems that human exploration of the universe will have to wait until we've worked out how to avoid the destructive deceleration of a spacecraft in an Alcubierre warp drive bubble."

    5 days ago
• Aseya Akbar

  How can we differentiate between ferrimagnetic and ferromagnetic hysteresis loop?

  for example i have got two M-H curves. can by just looking at curves we can say that its ferromagnetic or ferrimagentic in nature?

  Recent replies ⋅ Show All (5)

  • 
    Marek Wojciech Gutowski replied

    Well, ordinary X-ray examination is indeed unable to 'see' anything magnetic. But using polarized radiation you may be able to investigate MCD (magnetic circular dichroism) signal. I'm not sureWell, ordinary X-ray examination is indeed unable to 'see' anything magnetic. But using polarized radiation you may be able to investigate MCD (magnetic circular dichroism) signal. I'm not sure whether this technique distinguishes between various magnetic structures.

    5 days ago
• Inigo Valan

  What is the difference between matter wave of an electron and electromagnetic wave of a photo-electron?

  While studying Schrödinger's equations of wave, I had this question: This equation deals with waves, right then, can we apply it in the case of electromagnetic wave, but the equation deals with oneWhile studying Schrödinger's equations of wave, I had this question: This equation deals with waves, right then, can we apply it in the case of electromagnetic wave, but the equation deals with one particle system. What does this mean?

  Recent replies ⋅ Show All (14)

  • 
    Jose Pecina-Cruz replied

    Inigo, matter wave of an electron is lambda = (h-bar)/(mv), while a photon is absorbed totally by an electron. The electron obtained in this manner is called photo-electron. The first electronInigo, matter wave of an electron is lambda = (h-bar)/(mv), while a photon is absorbed totally by an electron. The electron obtained in this manner is called photo-electron. The first electron has a wave-length = (h-bar)/p, where p it is its momentum, if at rest p=0, but (Ee)^2 = (p^2)c^2 + (m0)^2(c^4), if p=0 =>E=m0c^2, but the photo-electron energy (Eph-e)^2=(p^2)c^2 + (m0)^2(c^4) + (Eph)^2, where Eph is the energy of the photon absorbed => (Eph-e)^2 = (m0)^2(c^4) + (Eph)^2 Therefore, they difference is Eph-e > Ee and lambda(e) ->infinite, lambda(ph-e) = finite

    7 days ago
• Vidit Katlana

  What changes do neutrinos effect when they pass from place to place?

  I want know whether they increase the temperature of the earth's crust if they are in great numbers when they come from the sun?

  Recent replies ⋅ Show All (3)

  • 
    Vidit Katlana replied

    Thank you Every one That helped me a lot

    7 days ago
• Mohamed E Kelabi

  Is it possible for a sound wave to be coherent?

  Can the direction of sound waves be controlled like (laser) light, so they can be guided in certain position?

  Recent replies ⋅ Show All (8)

  • 
    Ricardo dos Reis replied

    This kind of device? http://en.wikipedia.org/wiki/Long_Range_Acoustic_Device

    10 days ago
• Claudio Animato

  What do you think of the discovery of CERN and INFN about the velocity of neutrinos? It seems that they run faster than light

  Neutrinos run faster than light...

  Recent replies ⋅ Show All (501)

  • 
    Ulrich Mutze replied

    For each of us it may be instructive to recall honestly our thoughts and arguments from times when the story was still open.

    10 days ago
• Matias Leoni

  Why do you think that it is particularly physics the science which seems to show more proclivity to get surrounded by crackpots?

  Before answering this post, make yourself sure you are not a quack, else you shall be deleted. Please check: 't Hooft on bad physicists http://www.staff.science.uu.nl/~hooft101/theoristbad.html JohnBefore answering this post, make yourself sure you are not a quack, else you shall be deleted. Please check: 't Hooft on bad physicists http://www.staff.science.uu.nl/~hooft101/theoristbad.html John Baez crackpot guide http://math.ucr.edu/home/baez/crackpot.html Siegel's Are you a quack? http://insti.physics.sunysb.edu/~siegel/quack.html

  Recent replies ⋅ Show All (79)

  • 
    Marshall Barnes replied

    I think what's worse than so called crackpot theories are the mistakes that turn up in a a lot of work these days. The hidden assumptions and just plain running the train off the track thinkingI think what's worse than so called crackpot theories are the mistakes that turn up in a a lot of work these days. The hidden assumptions and just plain running the train off the track thinking sometimes. Stuff like "a clock is in the gravitational field of a neutron star and in front of a worm hole mouth. Outside the gravitational field some distance away is another clock in front of another wormhole mouth which is connected to the first. If you could go from the outside of one mouth to the other, you would see that the two clocks have different times but if you look at one from the other through the wormhole mouth, you would see they have the same time..." That's the kind of stuff I pay attention to. I couldn't care less about obvious cranks.

    10 days ago
• Philip Metzger

  Can neutrons jump between universes?

  A few years ago, physicists showed that it might be theoretically possible for neutrons to make the leap from our universe to a different one if the gravitational potential of an entire galaxy wereA few years ago, physicists showed that it might be theoretically possible for neutrons to make the leap from our universe to a different one if the gravitational potential of an entire galaxy were involved. Lucky for us, we happen to live in a galaxy so if we look closely enough, it should be possible to spot these neutrons jumping out of our galaxy. By watching a bunch of neutrons all at once, we might be able to experimentally verify whether any of them are disappearing off to alternate universes. How Neutrons Might Escape Into Another Universe: http://www.technologyreview.com/blog/arxiv/27517/ Attached is the full text for the publication: Experimental limits on neutron disappearance into another braneworld. Michael Sarrazin, Guillaume Pignol, Fabrice Petit, Valery V. Nesvizhevsky "Recent theoretical works have shown that matter swapping between two parallel braneworlds could occur under the influence of magnetic vector potentials. In our visible world, galactic magnetism possibly produces a huge magnetic potential. As a consequence, this paper discusses the possibility to observe neutron disappearance into another braneworld in certain circumstances. The setup under consideration involves stored ultracold neutrons - in a vessel - which should exhibit a non zero probability p to disappear into an invisible brane at each wall collision. An upper limit of p is assessed based on available experimental results. This value is then used to constrain the parameters of the theoretical model. Possible improvements of the experiments are discussed." Thoughts?

  1201.3949v1.pdf

  Recent replies ⋅ Show All (9)

  • 
    Gustavo Valdiviesso replied

    "In theory" means everything. At some moment in time, there always is as many theories that explain what we see as theories that predict unseen things. Actually, there might be even more. So with"In theory" means everything. At some moment in time, there always is as many theories that explain what we see as theories that predict unseen things. Actually, there might be even more. So with enough time, less than half of them will be right. But I ask you all to contribute positively to the discussions because calling every new possibility "science fiction" is as easy as it would be for your grand father, in your age, to say that "a device that has computing power, can take pictures, can communicate digitally with anyone in the world AND is also a phone" is science fiction. Moreover, criticizing without reading the reference is easy. Actually, I dare to say it is "lazy work". For instance, on section III.A of the cited paper, neutron decays are taken in account when calculating the probability for the neutron to swap between branes. So I ask you a little more politeness when inferring about the quality of the "so called scientist" of today. I read the paper and there is nothing wrong with it. It is, indeed, an interesting possibility, although we would have to extend the concept of energy conservation to multi-branes since our own brane would be losing mass. But, if we think about the two branes as equivalents, so in some point of our space we are acquiring some neutrons as well. So, in a global and statistical way, conservation of energy would still be holding on.

    18 days ago
• Anup Pattanaik

  If we will add Boron (dopant) to Silicon (pure) it becomes a semiconductor(impure). Is it possible in the reverse way? i.e adding Silicon (pure) with Boron (dopant), or it the same? Will it be aIf we will add Boron (dopant) to Silicon (pure) it becomes a semiconductor(impure). Is it possible in the reverse way? i.e adding Silicon (pure) with Boron (dopant), or it the same? Will it be a semiconductor or not?

  Recent replies ⋅ Show All (2)

  • 
    Inigo Valan replied

    In a semi-conducting silicon lattice by adding this Boron impurity it may increase or decrease the number of electrons thus changing the Band gap, But I don't think Boron to exhibit a similarIn a semi-conducting silicon lattice by adding this Boron impurity it may increase or decrease the number of electrons thus changing the Band gap, But I don't think Boron to exhibit a similar nature...

    20 days ago
• Vasuki Shankar

  What is the reason for Earth's magnetic field?

  What is the reason for its variable nature?

  Recent replies ⋅ Show All (17)

  • 
    William Jackson replied

    There is a nice graphic showing the correlation here: http://www.le.ac.uk/gl/ads/SiberianTraps/FBandME.html - a summaryThere is a nice graphic showing the correlation here: http://www.le.ac.uk/gl/ads/SiberianTraps/FBandME.html - a summary here: http://www.ccsf.edu/Departments/History_of_Time_and_Life/PDFs/FloodBasaltExtinctions12x24.pdf -------------- - a few random papers: http://www.scribd.com/doc/67472779/Courtillot-Renne-2003-On-the-Ages-of-Flood-Basalt-Events http://www.pnas.org/content/107/15/6555.full.pdf+html http://www.hcs.harvard.edu/~jus/0303/haggerty.pdf http://www.nhmus.hu/~palfy/palfy_etal_2002_gsaspecpap.pdf http://jpkc.nwu.edu.cn/stru/data/zlwx/zl/5.pdf http://www.clas.ufl.edu/users/eemartin/GLY5736F11/LIPs-ElementsMag.pdf http://geoweb.princeton.edu/research/Paleontology/Keller_AJES_05.pdf http://www.nature.com/nature/journal/v477/n7364/abs/nature10385.html http://muller.lbl.gov/papers/sciencespectra.htm -------------- A link to a paper that delineates the major extinction events, nicely: http://iod.ucsd.edu/courses/sio278/documents/veron_08_coral_reefs.pdf - some general information on flood basalts here: http://www.geolsoc.org.uk/gsl/education/flood_basalts_1 - information w.r.t. the end Triassic extinction event here: http://palaeo.gly.bris.ac.uk/Palaeofiles/Triassic/vulc.htm#The%20Effect%20of%20Volcanism: - an article here: http://blogs.scientificamerican.com/history-of-geology/2011/09/16/large-igneous-provinces-and-mass-extinctions/ - a map showing the extent of the C.A.M.P. flood basalts: http://www.auburn.edu/academic/science_math/res_area/geology/camp/Fig1.jpg - a paper w.r.t. C.A.M.P. here: http://jpkc.nwu.edu.cn/stru/data/zlwx/zl/5.pdf - link with some nice graphics w.r.t. climate change: http://www.friendsofscience.org/assets/documents/FOS%20Essay/Climate_Change_Science.html - a summary w.r.t SLIPs http://www.mantleplumes.org/SLIPs.html - others w.r.t. LIPs http://www.le.ac.uk/gl/ads/SiberianTraps/LIPS.html http://www.largeigneousprovinces.org/ - download .kml for GE here http://www.geology.sdsu.edu/kmlgeology/kmz/lip/lip.kmz http://www.geology.sdsu.edu/kmlgeology/kmz/hotspots/hot_spots.kmz --------------- For more information w.r.t. the volcanism hypothesis, try searches like: http://duckduckgo.com/?q=Mass+extinctions+and+ocean+acidification&t=lm http://duckduckgo.com/?t=lm&q=Anoxic+event+flood+basalts&t=lm http://duckduckgo.com/?q=Mass+extinctions+and+flood+basalts&t=lm http://duckduckgo.com/?t=lm&q=Large+igneous+provinces+and+mass+extinctions&t=lm

    23 days ago