# 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. ### 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...
2. ### 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: $$f_2=\frac{v-0.1v}{v}f_o$$...
3. ### 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...
4. ### 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?
5. ### 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?
6. ### 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?
7. ### 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?
8. ### 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?
9. ### I Lorentz transform gone wrong

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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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...
14. ### What is the volume of the system when inserting the 4-velocity of the observer?

I have attempted but with no result.
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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?
19. ### 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...
20. ### 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...
21. ### 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 -...
22. ### 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...
23. ### 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...
24. ### 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...
25. ### 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...
26. ### 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...
27. ### 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...
28. ### 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...
29. ### 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...
30. ### 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...
31. ### 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...
32. ### 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...
33. ### 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...
34. ### 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...

36. ### 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}##...
37. ### 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...
38. ### 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...
39. ### 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...
40. ### 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...
41. ### 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...
42. ### Special relativity — Observer measuring the velocity of a passing rocket

I am a little confused with the text above. Actually, all is ok until 2.51, i think i am missing something. What is this? Another way to define gamma? (The doubt is not about the raising indices, neither about "n00 = -1", is just where does the equation came from. That is, the equation is easy...
43. ### B Metric tensor for a uniformly accelerated observer

Hello all, let's suppose we have, in a flat spacetime, two observers O and O', the latter speeding away from O, with an uniform acceleration ##a##. In the Minkowski spacetime chart of O, the world-line of O' can be drawn as a parable. We know that the Lorentz boost at every point of the...
44. ### B Light's Speed & Moving Observer: What Happens?

for example the car headlight would look faster then c speed. (it speed would be the speed of light +the speed of the car) to observer in front the car. because the light come from the car so the speed of the car would connect with light speed (like when you walk on a train) . so does the light...
45. ### I Speed of light for a Rindler observer

I've read that speed of light for a Rindler observer is not constant. I wasn't sure why and I tried to do this as an exercise for myself, I think I came with the correct answer, but I'm not sure, is the following argument correct? Let's describe the (flat) space-time using Rindler coordinates...
46. ### Frequency of sound received by an observer

My thought process was this, They are asking us to find the frequency of sound received by observer when the source reaches at origin. According to me when the source reaches origin there would be no component of source's velocity in the direction of observer, hence vs=0 vo=0 since the observer...
47. ### Lorentz transformation for an approaching observer

I think this should be t'= Lorentz factor* (1+v/c)t, but that doesn't make sense to me.
48. ### B How does an isolated observer know if they're accelerating?

I'm reading a book on principles of relativity, and am going through the definitions of reference frames and free particles. From what I've understood from there and other answers on SE, a non-inertial reference frame is one in which a free particle is measured to be undergoing acceleration...
49. ### I Basic observer effect questions

What counts as an observer, and what does it mean to "observe"? I've read a detector (machine) is an "observer." But how do we know it performed an observation without observing it? Is it possible our observation of the detector retroactively caused the wave function to collapse?
50. ### I Wigner's Friend shows the difference between Observer and Measurement

You often hear this debate about the role of the observer in Quantum Mechanics. How you view this role is usually dictates the interpretation you prefer. If it's Copenhagen, then the observer is more robust and plays a crucial role in wave function collapse. If it's Many Worlds, then the...