What is Observer: Definition and 322 Discussions

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. entropy1

    I Observer superposition in MWI?

    In MWI, would you say that a measurement puts the observer in superposition of being in the various worldlines? If I said "yes" to that, would I be correct?
  2. DennisN

    I An observer passing the event horizon of a black hole (Part 2)

    Hi all, this is a new scenario I got thinking about after having received great feedback and corrections from other PF'ers in this thread. Thanks again for the great help! This new scenario is similar to the previous one, but with a twist including a mirror. And as I said in that thread, I am...
  3. DennisN

    I An observer passing the event horizon of a black hole

    Hi all, I've just read this entire thread and watched the videos about black holes posted by @PeroK, which I liked very much (thanks @PeroK! :smile:). I am not particularly well aquainted with GR and my questions are concerning the often mentioned statement that an observer that passes the...
  4. Quantum Alchemy

    I A question about Many Worlds and my Remote Control

    I get so many different answers to this question so maybe here someone can pin this down. When I get up in the morning and I turn on my TV, I have over 3,000 channels so is there a universe with a version of me going to each channel? If not, how do I go to one channel over the other? Can my...
  5. Hawzhin Blanca

    A Many worlds, observer and Entropy

    According to Everett-interpretation or many world interpretation of quantum mechanics, each decision an observer makes, the world splits into two parallel universes, let’s say an observer in some point in Spacetime is tests the Schrödinger’s cat experiment, in one branch of the universe the cat...
  6. D

    Help with Length contraction of ruler at 60degree angle to observer

  7. K

    I Communication with Rindler Observer: Is It Possible?

    Is it possible that some light signals will never reach the Rindler observer? Just to be clear, by Rindler observer I mean an observer undergoing constant acceleration (as measured in his own rest frame).
  8. Arman777

    I How Does Time Dilation Affect Space Travel Duration?

    Let us suppose a spaceship moving from Earth to another star that is 10ly away with a speed of 0.99c. Calculate the of years spaceship takes to reach its destination (a) in the rest frame of an observer on Earth and (b) as perceived by a passenger on board the ship For (a) I find that ##t_0 =...
  9. K

    B Doppler Effect: Light Blueshifted When Source Moving Towards Observer

    If I and the light source are both moving toward one another, I see light blueshifted. What if I'm at rest and the source moving towards me?
  10. jybe

    Sound Interference Problem -- Observer moving between two speakers

    Homework Statement Two identical loudspeakers are driven in phase by the same amplifier at a frequency of 680 Hz. The speakers are 4.6 m apart. An observer stands 9 m away from one of the speakers as shown. The observer then starts moving directly towards the closest speaker. How far does the...
  11. Machine1701

    I Why doesn't decoherence apply to unobserved experiments?

    This is based on the Hugh Everetts interpretation of quantum mechanics, where the waveform never collapses but the observer becomes a part of it, thus experiencing decoherence of the wave form from their point of view. So, let's say someone is doing the two-slit experiment. The particles going...
  12. G

    B Can an observer perceive he is traveling faster than light?

    I have seen thought problems with an observer on a train or in a station, etc., but I have not seen ones with the observer traveling at relativistic speeds. It seems to me that at sufficient speed he would observe himself exceeding the speed of light due to the slowing of time. This seems like...
  13. R

    B Is there an experiment proving observer dependency exists?

    The idea of the outcome of an experiment depending on whether or not it is being observed is strange. I have never seen this happening in real live. Still in physics it is held that it does exist: the double slit experiment using very low-energy laser light (assuming that one photon passes the...
  14. H

    B An observer looking at Earth's past history

    I was thinking about the signals Mankind has sent out from Earth greeting other races out there. Is it reasonable to think that even if some being received the signals (data) they would have no idea about locating Earth because it would be in somewhere else in the Galaxy/Universe by then? So...
  15. R

    B Speed of Light Slowed for SuperBig Observer?

    How fast would the light travel for a SuperBig observer... immagine his head is the size of the Sun, and he is sitting in a room, then he decides to turn on the light in the room... if he is so big, would he have to wait some seconds until the light reaches his eyes? Would it mean that for this...
  16. S

    B What is the role of a non-real observer in mathematical thinking?

    ?
  17. Kenneth Boon Faker

    A question about wave/particle duality

    Subatomic particles can take the form of a wave or a particle. While in wave form, it is not like a physical wave, but rather a probability wave, (i.e. a wave of information about where the particle is probably located etc.) And while in particle form, a photon, for example, can knock electrons...
  18. Kenneth Boon Faker

    B Subatomic particles and the observer

    I have read that when an electron is observed, it behaves differently to when it is not being observed. Could someone please expand on this, or indeed correct me. In what way does an observed particle behave differently to a particle that isn't being observed by somebody's consciousness?
  19. J

    B Understanding The Conscious Observer: Young's Double Slit Experiment

    How exactly does the mere act of observing collapse the wave function of, say, photons? I don't quite understand that one. And Richard Feynman's question related to Young's double slit experiment and the fact the electron went through both slits, as well as neither, and just one slit, and just...
  20. D

    B Temperature of a black hole....observed from the singularity

    I'm just a layman here, who enjoys science and astronomy. I was reading about the temperatures of the cores of black holes being extremely cold, and how time at the singularity...progresses super, super slowly. But this is only as measured from an outside observer's perspective (such as from a...
  21. Arman777

    I Why the speed of light is constant for every observer?

    Why the speed of light is constant for every observer ? Is it a special thing for photons cause I guess there's no other elementry particle that can move with c ? Also I want to investigate the constant of c for every observer, in the perspective of particle relationship. For example, can I...
  22. T

    I Is my thought right or wrong? Light and a moving observer

    I would like to know whether my thought is right or wrong about time dilation example. Let's say, A person is standing at a starting point so his velocity is 0 ms'1. A car runs from that point in the velocity of 3 ms'1. A photon from a light source at that point is also emitted at the same...
  23. Kara386

    I Calculate Time at Infinity for GR Observer: A Photon's Journey

    We were shown the answer to this question as a worked example: A photon is emitted from a radius ##r_2## and travels radially inward to ##r_1## until it's reflected by a fixed mirror and travels back to ##r_2##. Calculate the time taken for the photon to travel in and back, according to a...
  24. sergiokapone

    I Velocity measurement by a stationary observer in GR

    In almost general case, the space-time metrics looks like: \begin{equation} ds^2 = g_{00}(dx^0)^2 + 2g_{0i}dx^0dx^i + g_{ik}dx^idx^k, \end{equation} where ##i,k = 1 \ldots 3## - are spatial indeces. The spatial distance between points (as determined, for example, by the stationary observer)...
  25. P

    Sliding mode observer gain -- How do I find it?

    Hi, I have a 2nd order of sliding mode observer of the form: \dot{\hat{x}} = \hat{f}(x,t) + \delta f + \Psi(u,y) +[ \frac{d \Omega}{dx}]^{-1} \upsilon where ##\upsilon##: \upsilon_1= \alpha_1 \lambda_1^{1/2} | y_1 -\hat{x}_1|^{1/2}*sign(y_1 -\hat{x}_1) \upsilon_2= \alpha_2...
  26. B

    I Does Conscious Observation Affect the Outcome of the Double-Slit Experiment?

    Hello there, My question is: Is there a double slit-experiment done with all of the measuring equipment in place and all of the equipment activated but without a conscious observer? Proving there is no differentation pattern regardless of a conscious observer. Thanks in advance
  27. Talisman

    I On being the sole observer in MWI

    Hi all, Suppose we have some particle in state $$|\Psi\rangle=\frac{1}{\sqrt{2}} (|U\rangle + |D\rangle)$$ It starts interacting with its environment, including Experimenter 1 (E1). From Experimenter 2's viewpoint, this can be represented as: $$|\Psi\rangle=\frac{1}{\sqrt{2}} (|U\rangle...
  28. P

    MATLAB Sliding mode observer in Matlab or Simulink

    Hi, I have designed a variable-based observer analytically on paper. Now it's time to implement it in Simulink/matlab. Suppose we have followings in a tire model. The EOM says: J\dot{\omega} = T-R_eF_x m\dot{v}_x = F_x where J is the inertia of the wheel, \omega is the angular velocity , m is...
  29. victorhugo

    B Question about the Heisenberg U.P. & the Observer Effect

    I studied only half a semester of quantum physics in high school (which i only finished 8 months ago and came first in physics luckily) but i remember Heisenberg's uncertainty principle. All over youtube people were saying things like "this is God's way of keeping us from getting into perfection...
  30. Pushoam

    How does relativity affect the observation of moving objects?

    Homework Statement A.P. French q.no. 4.3 Homework Equations t = L\c, (1) L0 = ϒ L The Attempt at a Solution The observer's frame is that frame w.r.t. which the meter stick is moving with speed 0.8c. The observer sees the mid-point at (x,y) at a time to(measured from the clock situated at...
  31. A

    B Wave-particle-duality and the evolution of the universe

    If I've understood correct, every particle in the universe exists in a waveform, which I've understood to mean propability where the particle does exist? Then which I've understood is, that the wave transforms into a particle only when observed, is this correct? Then if it is correct, how...
  32. A

    B Is a "meter" observer dependent?

    SI defines one meter as the distance traveled by light in one upon 299792458(=k) seconds, from which we get that, D=c*k, where k is marked above. So, let's consider two frames on at rest wrt the earth(f1) and another moving at, say 0.99*c(f2). SR says that the time dilates for f2 wrt f1. And...
  33. J

    A General relativity -- Proof of energy measured by observer

    I want to prove that ##E = -g_{\mu \nu}u^\mu p^\nu## is the energy measured by an observer with velocity ##u^\mu## of an object with momentum ##p^\mu##. My reasoning is that in special relativity we know that ##\gamma m = E##. We can transform to coordinates where ##u'^\mu = (1,\vec{0})##. Since...
  34. T

    B Finding the distance of two points from observer

    Lets suppose that two points A and B are very close together compared to their distance from an observer who is very far. Suppose the distance from observer to point A is DA and to point B is DB. How precisely we can find the distances separately.
  35. D

    I How important is light in the Observer Effect?

    How much importance does light (electromagnetism) have to do with the "Observer Effect" in the Double-slit experiment? From my research, it seems that the only successful "Observer Effects" in the Double-slit experiments, wherein, the interference pattern transitions to a clump pattern, is...
  36. N

    B What happens if the observer dies?

    Basic double slit experiment one observer knows the path of the particle. The back screen is a locked room and has never been seen. The observer dies and I decide to look at the screen. What will I see? I'm assuming the wave will still be collapsed.
  37. A. Neumaier

    A States in relativistic quantum field theory

    No. This is a noncovariant, observer-specific view.In the covariant, observer-independent view of fields, states are labeled instead by the causal classical solutions of hyperbolic field equations. On the collection of these the Peierls bracket is defined, which is the covariant version of the...
  38. Jilang

    I Is the state observer dependent

    I was just reading the thread about the dead cat/live cat. Is the state of the cat dependent on the knowledge of the observer?
  39. QuarkDecay

    B Doppler effect/ both moving same direction

    What happens if a source and the observer move at the same direction? Always hear how only one of them doesnot move, or when they move towards each other. For example. An ambulance moves towards direction A with Va. A biker moves towards direction A as well, with Vb. What happens to the...
  40. newrd

    B Who was the observer for the first 10 billion years?

    If reality requires an observer, and life on Earth is only 3.8 billion years old- yet the universe is 13.8 billion years old, who was the observer for the first 10 billion years?
  41. Drakkith

    I Age of the Universe as Measured by a Non-Co-Moving Observer

    In a recent thread I incorrectly stated that an observer moving at a high velocity relative to a co-moving observer would measure the age of the universe as more than the co-moving observer would. Apparently that is incorrect, and the age of the universe measured by the first observer would be...
  42. L

    I Universe is a sphere that is centered on any observer? How?

    I read here, http://www.space.com/24781-big-bang-theory-alternatives-infographic.html , that, "What we call the "observable universe" (or the "Hubble Volume") is the spherical region, about 90 billion light-years in diameter, that is centered on any given observer. This is the only part of the...
  43. S

    Relativity - velocity of object travelling perpendicular to the observer

    Homework Statement Two light beams collide head on. Calculate their relative velocity. (c) A particle moves north at speed 0.85c relative to an observer standing on the Earth. What is the velocity of this particle as observed by a fast ship traveling east on the Earth at speed 0.9c? Give the...
  44. BiGyElLoWhAt

    I Doppler shift for an observer in circular motion

    Say we have an observer in perfectly circular motion around a source, like a star. Is it reasonable to apply the angle change formula ##cos \theta_o = \frac{cos \theta_s - \frac{v}{c}}{1-\frac{v}{c}cos \theta_s}## and then take the component of the motion parallel to the light wave in the...
  45. phinds

    I Remote observer sees black hole evaporate

    In a couple of recent threads, I have attempted, unsuccessfully, to elicit a response to the following, which is my belief about why an observer standing well off from a black hole will in fact see the black hole evaporate (over a LONG period of time, of course, so the observer has to have an...
  46. S

    A Symmetry considerations between observer and observed in QM

    The following is taken from page 101 of Warren Siegel's textbook 'Fields.' Another example is quantum mechanics, where the arbitrariness of the phase of the wave function can be considered a symmetry: Although quantum mechanics can be reformulated in terms of phase-invariant probabilities...
  47. S

    B Moving clock as seen by an observer at rest

    Please forgive me if this has been asked before. I understand that a clock that is moving relative to an observer at rest will slow down. If the moving clock is in a transparent rocket, would the stationary observer on the ground see the moving clock slow down physically?
  48. adfreeman

    Mind over matter reality or myth?

    Hi, I’m new to the forum and I would like to ask some questions. I’m not a physicist –for some reason that I’ll always regret I chose Business Studies- and my knowledge of physics is limited to high school, physics books and documentaries; which I must have watched them all by now. Anyway, for...
  49. valentin mano

    Observer Falling Into a Black Hole -- What do they see?

    If we have an infalling observer through the event horizon,will she see the end of the Universe?
  50. N

    Observer dependent event horizon for Schwarzschild black hole

    Hello. In oral exams my professor likes to ask if Alice and Bob can communicate, if Alice ist just above the event horizon of a schwarzschild black hole and Bob ist just below. He wants to hear: Communication is possible, because the event horizon is observer dependent. Only an observer...
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