Observer Definition and 331 Threads

The Observer is a British newspaper published on Sundays. In the same place on the political spectrum as its sister papers The Guardian and The Guardian Weekly, whose parent company Guardian Media Group Limited acquired it in 1993, it takes a social liberal or social democratic line on most issues. First published in 1791, it is the world's oldest Sunday newspaper.

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  1. S

    Siren frequency heard by observer when an ambulance passes

    I am not sure I understand the question. Based on "The ambulance travels towards, passes close to, and then travels away from a stationary observer", I would answer greater than f then less than f. If based on "as the ambulance passes the observer", I would say less than f and constant (option...
  2. e0ne199

    MATLAB Unable to produce desired results using state-space model with observer for inverted pendulum

    Hello everyone, I am trying to make a state-space observer of inverted pendulum using this code : and I connect it to this model : but somehow I am only able to produce this result : Do you know what is actually wrong with my code?? any response and help is really appreciated..thanks before
  3. S

    I Speed of information-carrying radiation

    How can an approaching observer receive the information from a source at a higher rate (as an accelerated recording), while the information-carrying radiation could not?
  4. S

    B Speed of light seen by a moving observer

    How can the speed of light remain the same for an observer while the duration of a light beam is shorter if you move towards the light, and longer if you move with the light? The light beam remains the same length.
  5. James Halifko

    How Does Lifelong Curiosity Shape Our Understanding of Modern Physics?

    I have been curious for as long as I can remember: at least 70 years now. My life has been an eclectic collection of adventures and studies, not all in an academic sense. I have a background in electronics, an AA in Physics (A simple comment marriage sidetracked my formal education), a US Army...
  6. A

    B Is this an Unavoidable Collision between 2 spaceships traveling at 0.6c each?

    Relativity always talks in terms of observer but fail to explain common sense problems like this. The fact that no one can measure anything faster than light does not preclude to objects moving towards each other at a higher velocity than an external observer can measure. Move the observer to...
  7. S

    Why is the "conscious observer" thing considered?

    Question from someone scarcely more knowledgeable on QM than a layperson. To my understanding, early in QM's study, some thought observation by a conscious being was required to collapse a wave function. I was told here that said Copenhagen interpretation(?) is only considered by people like...
  8. M

    B Falling into a black hole

    If, from an outsider's perspective it takes an infinite amount of time to cross the event horizon, but a finite amount of time for the black hole to evaporate, how does that look like from the perspective of the falling observer. For that matter, how does it look like from the perspective of the...
  9. M

    Stationary observer meaning in relativity problem

    For this problem, I don't understand what it means by the notation of a "stationary" observer. I thought there was no such thing as absolute rest. Does someone please know whether it means stationary with respect to the object? Thanks!
  10. R

    I A question about Relativity of Time using Time dilation experiment

    The time dilation experiment involves two frames in relative motion, let one at ground and other at train with velocity V. The light clock runs faster in rest frame, as seen by an observer A at rest in train ( just beside clock ) than that observed by an observer B in ground frame which observes...
  11. S

    Range of frequency heard by observer related to Doppler effect

    My answer is (A) but the correct answer is (B). My attempt: $$f_2=\frac{v\pm v_o}{v\pm v_s}f_1$$ $$=\frac{v+0.1v}{v}f_o$$ $$=1.1f_o$$ If we consider the observer to move pass through the sound source and now is moving away from the stationary source, then: $$f_2=\frac{v-0.1v}{v}f_o$$...
  12. MatinSAR

    Question about time dilation

    My try which was failed : Observer at rest measures time ##\Delta {t'}= 2.2 \mu s## In the frame of reference of the Earth observer measures time ##\Delta t=\dfrac {\Delta {t'}}{\sqrt {1-u^2/c^2}}## I have two unknowns ##u## and ##\Delta t## so I cannot find ##u##. Is there another equation...
  13. S

    I Does Schrodinger's Cat contradict itself?

    In the schrodinger's cat thought experiment is the cat technically the observer because The cat can observe if its alive or dyeing? Should schrodinger's thought experiment only work with non living objects?
  14. E

    A Movement vs expansion in space

    How can an observer distinguish two objects that are moving from each other in space compared to those that are moving with space due to expansion of the universe?
  15. mister i

    B Does the age of the Universe differ for observers in expanding space?

    The age of the universe is said to be about 13.8 billion years. But, since time depends on the observer, would it be the same for a possible inhabitant of a planet in a galaxy about 10,000 million light years away that is separating from us at 60% of the speed of light?
  16. Hill

    I Interpretation of (X,T) coordinates in Kruskal diagram

    These are the points in the book: What is "naturally used"? Does it hold only as the observer crosses the event horizon? How can they "use" them?
  17. S

    I Exploring Wave Function Collapse: The Role of Conscious Observation

    Do scientists still entertain the idea that wave function collapse requires a conscious observer? Is it possible? Why/not?
  18. Physicsperson123

    I Why Do Some Events in My Lorentz Transformation Appear Incorrect?

    Here is the space-time diagram of an observer: Here is the diagram as seen by an observer travelling from left to right: I have attempted to represent the axis system of the moving observer on the axis system of the stationary observer in the following diagram: Event D seems to lie in...
  19. F

    B Further Understanding Simultaneity Conventions

    Summary Almost a year ago, I created a post titled “Understanding the phrase 'simultaneity convention'”. The answers included requirements for defining a simultaneity convention. But some simultaneity conventions, while meeting all the requirements, still appear problematic. What am I missing...
  20. K

    I How does an observer moving at relativistic speeds perceive a pulsar?

    Let us suppose our velocity towards a distant neutron star roughly equated to a dilation factor of 10. On board our vessel we are equipped with a NIST-F2 atomic clock . Since the clock travels with us, it also experiences the same dilation; thus, in our frame, the clock keeps time the same as...
  21. S

    I Fuel paradox arising from Galilean transformation?

    I have encountered a problem related to the Galilean Transformation. Let's consider two observers who will be referred to as ##O## and ##O^{'}##, with their corresponding coordinates ##(t,x,y,z)## and ##(t^{′},x^{′},y^{′},z^{'})## respectively. They are initially at the same location, at time...
  22. B

    Decoherence vs Observer Wave Function Collapse & MWI: Questions

    I have a couple of questions about decoherence vs. observer wave function collapse and multi-worlds interpretation. Am I right that Zeh's decoherence theory does not involve an observer, and esp not a conscious observer? Also, am I right that his theory does not involve or align with the...
  23. StenEdeback

    What is the volume of the system when inserting the 4-velocity of the observer?

    I have attempted but with no result.
  24. G

    Which hemisphere is the observer?

    TL;DR Summary: Astro Olympiad Problem determining the latitude of an observer from a picture taken. Well this question and answer are really confusing. There are no cardinal directions labelled on the picture. However because the Sun and the Moon should move on a circular path, the left side...
  25. V

    Flag orientation for a boat observer Vs a ground observer

    I am confused by the question. So, the first thing I am trying to understand is whether the flag direction will be same to a boat observer as to a ground observer. I know that the flag will orient itself in the direction the wind is blowing towards, so the flag should always point in NE...
  26. M

    Non-inertial observer inside train

    For part (c) of this problem, The solution is, However, how did they know that the fictitious force that acts on the mass until the string become taut (T = Ma from as observed by an observer at rest outside) has a magnitude of Ma (assuming that the observer has no communication with the...
  27. J

    I Observer effect in the Dual Slit experiment

    How detectors/observers in front of each slit works , does it somehow disturb with electron/photon? Does photon/electron must pass through detector/observer, so maybe his internal parts change final result on screen into just two lines?
  28. B

    I Observing a Collapsing Shell: Time Dilation Explained

    What does and observer inside of a collapsing shell observe? Lets say we have a shell of matter collapsing to a black hole. What would observers near the center see? How would the rest of the universe appear when, The shell is approaching the Schwarzschild radius? After the shell passes the...
  29. Onyx

    I Appearance of Warp Bubble Internal Volume to Distant Observer

    At a single moment of coordinate time ##t##, would a distant observer perceive a warp bubble's interior volume as blown up, or would it seem compressed? Looking in the catalogue of spacetimes at the static local tetrad of the Alcubierre metric, the ##e^x_{(x)}## leads me to think that a static...
  30. D

    I HUP and the observer effect

    The observer effect results from the interaction of a quantum system with a measurement device. The HUP is more fundamental: it results from the fact that certain quantum measurements cannot be made simultaneously (or, equivalently: certain quantum observables do not commute, most famously -...
  31. Tertius

    I Co-Moving Coordinates & Lapse Function N(t) in ADM Decomposition

    In the ADM decomposition, like in the construction of the FRW metric, the coordinates are defined to be co-moving, so we know $$d\tau = dt$$ (i.e. the lapse function is normalized away) Starting from a five-dimensional embedded hyperboloid (as in carroll pg. 324) ## -u^2 + x^2 + y^2 + z^2 + w^2...
  32. guyvsdcsniper

    Find the contraction of angles seen by an observer

    I am trying to follow the work to this question but am stumped at steps 3 and 4. I am confused as to where the cos^2(90+θ) comes from? I can see it is used to invoke sin into the equation since we have that value. Is it because we are only measuring the x-component of the movement, so we need...
  33. Istiak

    Find out velocity of an observer (relativity)

    Initial observer is at rest. So ##x\prime=0##, and according to question they are 10 meter apart. So lorentz transformation becomes ##vt=x## ##v=\frac{x}{t}## ##=\frac{10 \\ \mathrm m}{13\times10^{-9} \mathrm s}## But I don't get the expected answer. I believe if I had took ##\beta c## instead...
  34. L

    I Can configuration space be observer independent?

    We can formulate the spacetime in an observer/coordinate independent way, i.e. a particle becomes a worldline in the 4d space. Then relative to each observer, the worldline can be casted to a function in R^3. However, I haven't found any reference on formulating configuration space in a...
  35. F

    I How things appear to an accelerated observer

    I've been working on a Minkowsky spacetime diagram generator. The software is probably way overkill, but I'm retired and it keeps my brain active. I am no physicist, but I am a pretty good programmer. Side note: if you have any interesting things to diagram on a 2D Minkowsky spacetime diagram...
  36. T

    I Observer Inside Collapsing Shell

    let's consider spherically symmetrical thin shell of dust, which is collapsing under its own gravity. There are no other forces as pressure or so except gravity, and particles of shell (dust) are in free fall. The shell has total mass M and collapse starts from rest state with diameter of the...
  37. PainterGuy

    What is the "observer" in PID control?

    Hi, The sentence in red confused me. I've basic knowledge of control theory so, if you can, please keep it simple. I understand that with pole-placement regulator (LPR) and linear quadric regulator (LQR) one can use an observer to estimate the system's internal states rather than measuring...
  38. Roberto Pavani

    B Exploring Time and Space Dilatation Near Black Hole Event Horizon

    As closer the observer will be to the event horizon, the more the time dilatation will be. As we know, if the observer O1 has a clock, another observer O2 very far from the black hole will se the O1 clock "slowing" down as O1 approach the event horizon. The limit is that the O1 clock "stops" at...
  39. H

    A Ising lattice seen by an inertial observer

    We have an Ising lattice on the x-axis . on every site there is an atom which can be up or down. i suppose that there are N atoms (repetedly with the same values). Each sequence of spins has an energy H with a probability exp(-H/k T) i suppose that there is a device attached to each atom...
  40. D

    B Understanding the Observer in Quantum Mechanics: Debunking Common Misconceptions

    Im confused What collaspes the wave function ... is it a human eye ball or physical measuring device. The way QM is described on youtube for layfolks is not very good. They make it sound like the physical observer collaspes the wave function ... however its a physical device interacting with...
  41. M

    I Observe Hawking Rad. in Black Hole?

    Theoretically could an observer in a black hole perceive hawking radiation escaping the black hole as a black hole within the black hole? Also if so maybe that black hole could produce a radiation similar to or related to hawking radiation (Making a strange entangled system for conservation of...
  42. V

    Forces on particle in complex motion relative to ground observer

    A table with smooth horizontal surface is fixed in a cabin that rotates with a uniform angular velocity ω in a circular path of radius R. A smooth horizontal groove AB of length L(<<R) is made on the surface of the table. The groove makes an angle θ with the radius OA of the circle in which the...
  43. I

    B Time Dilation: Away or Toward Observer?

    I thought the answer was no. I.e. the traveler's proper time always passes more slowly than a stationary observer's clock regardless of the traveler's direction with respect to the observer. I was watching Brian Greene's NOVA episode on time, however, and, at 23:15, he has a demonstration...
  44. robphy

    Insights The Electric Field Seen by an Observer: A Relativistic Calculation with Tensors

    Continue reading...
  45. A

    I Electric Field seen by an observer in motion

    In Robert Wald's General Relativity textbook page 64 reads: __________________________ In prerelativity physics, the electric field ##\vec{E}## and magnetic field ##\vec{B}## each are spatial vectors. In special relativity these fields are combined into a single spacetime tensor field ##F_{ab}##...
  46. V

    Law of inertia (inertial observer and inertial frames of reference)

    I am trying to figure out what are inertial observer and inertial frames of reference. The law of inertia holds for inertial observers. Inertial observers are objects with zero net force acting on them, and move with constant velocity. Suppose we fix a set of coordinate axis in space, relative...
  47. B

    B Anthropological Influence on Culture: Exploring the Observer Paradox

    When an anthropologist analyzes a culture he/she might influence it and so does not get an accurate understanding of that culture. Does that mean that there was no specific culture before the anthropologist arrived? NO! Similarly, why would someone say that a particle has no position before...
  48. S

    B Event horizon for observer within main horizon

    The event horizon of a black hole is defined with respect to observers far away, and we know that light from within the horizon can't reach a distant observer. But what if an observer is within the "main" event horizon? Presumably, there will be another horizon nearer to the center, such that...
  49. M

    I Precession of Mercury: Adaptation for Observers

    For the observation of the gravitational redshift one needs an adaptation of the GTR of the object (related to the Sun´s gravity) and the observer (related to the Earth’s gravity). I assume that the situation is similar for the observation of the precession of Mercury, another experiment...
  50. entropy1

    I The need for a "conscious observer"

    Does unitarity of the evolution of wavefunction get rid of the need for a "conscious observer", and does collapse in contrast demand a "conscious observer"? For with unitarity there are is no requirement for such an observer, and collapse can't be explained without such an observer. The...
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