Observer Definition and 324 Threads

If yes, does dark energy define a frame of absolute rest? In the Einstein field equations, the cosmological constant is just a scalar, so it is independent of frame. But, sometimes, the cosmological constant is described as being a kind of vacuum energy density. Wouldn't a vacuum energy...

hello i have this question " a liquid has refractive index (n). find the refractive index of this liquid for an observer if the liquid have a velocity (v) to this observer " i have my solution in an attachment please look at it and tell me if it is the right solution thank you...

Uncertainty principle -- Nature of observer About the fact that electrons have a determined position only after having been observed/measured, I don't understand how they make the difference between being watched by an eye/instrument or any non-measuring object just sitting there.

Let's imagine a rocket orbiting the earth. The rocket could be any real rocket with moderate speed, so that relativistic effects are not significant, and also rocket does not experice notable centrifugal or other acceleration (so the rockets reference frame would appear almost inertial). A...

Yesterday, I read about Hawking's new proposal regarding the firewall paradox. A more general thought about standard black holes occurred to me. Black holes including stellar black holes are of course always presented as if the event horizon is an invisible barrier, which the unfortunate...

We are trying to find the relative velocity in a Lemaitre observer's frame, when said observer passes an observer dropped from rest at Painleve radius r_0. I have searched for related previous posts, found some, but none that clarified this particular situation. Let the passing happens at 0 < r...

Hey guys, I've been trying to find out an answer to this question I had today but couldn't find it. The question is regarding the measurement problem and the observer effect for the double slit experiment. Say I have 2 electron detectors labeled A and B respectively. Detector A is located at the...

Textbooks like Landau and Lifshitz avoid the observer having to be conscious, by saying a measurement is the interaction of a quantum system with classical apparatus to produce a classical result. However, there is an analogy that is often drawn that wave function collapse is like statistical...

Hey guys. I have a question regarding exercise 6.5 in MTW ("Radar Distance Indicator"). The exercise asks the following: http://postimg.org/image/lkn2oujc5/; I did the problem several different ways and I always end up at the same final equation relating ##L_0## to ##L##, an equation which...

Hi In double slit experiment our observe can change the past and in the entanglement our observe affact other particle pair. How could such a thing possible ?

Homework Statement A source of sound emits waves at a frequency f 450 Hz. An observer is located at a distance d 150 m from the source. If the observer is moving away from the source at a velocity vobs 40 m/s, how does the number of wavefronts change with time? dN/dt ? (in Hz)...

Could the "hidden variables" be encoded in the observer? The hidden variables that have been proposed to dictate the action of quantum outcomes, Could they be in observer dependent as opposed to encoded in the particle? We know the observer is an integral part of the process. Has this...

Homework Statement We are given that a light-bulb radiates 0.1 W from it, and the wavelength of light emitted from it is 530 nm. Seeing as the human eye requires around 6 photons per second for the brain to register a light signal. I am then asked, what is the largest possible distance...

Would someone help me to understand what would happen in this situation. w→ x→ (y)→ z Photon emitter is at point w emitting photons one at a time. Double slit is at point x. Screen is at point z. There is a detector at point y (after photon has already passed through slits) which is capable...

What values of right ascension are best for viewing by an observer at 40 degrees north latitude in January? I found this problem in the "Introduction for the Modern Astrophysics". I'm stuck with this problem because I don't know how to relate the right ascension and latitude.

I'm studying quantum mechanics and I can't seem to understand what qualifies as an observer. Does the "observer" need to be a conscious one? Yes or no and why? Thanks in advance :)

"Proper Reference Frame"-Accelerated observer Hi guys. This is regarding section 13.6 (p.327) in MTW. Here the authors consider an arbitrary accelerated observer in any space-time and construct a set of local coordinates carried along the entire worldline of the oberver with the origin of the...

I have seen many programs on Quantum Physics suggesting that we are the Observer that causes the collapse of the wave function. When I look into the experiments it seems more like the thing that causes the collapse of the wave function is other waves smashing into them. For instance in the...

Hi all, Please forgive my simplistic understanding on this, as I am a novice with an interest in Science, but I have the following question: I've been reading a book on Einstein, and here's the stuff I get: Speed is relative since there is nothing to "fix" a grid to which we know to be...

Imagine that we have a system that consists of a massive black hole, and the asteroid revolving around it on a stable orbit. What method can determine the distance to these asteroids observer who is still close to the event horizon? The first thing that came to mind is to determine the signal...

This is a basic question regarding Lorentz transformations. Let's say we have two observers - S on Earth and S' which we put on a rocket headed for Alpha Centauri (A.C) =). If i choose 2 events like this: rocket leaves Earth rocket arrives on A.C These two events clearly do not...

Hi! I was doing some exercises about the doppler effect on sound until I found this problem that I can't find the solution! "A source of sound of frequency f0 moves horizontally at constant speed u in the x direction at a distance h above the ground. An observer is situated on the ground at...

Suppose we have a spacetime diagram like this: Red lines indicating light travel from the moving object to the observer. Object is moving at the speed of 0.8c. At this speed we have: Lorentz factor 1/√(1 - v2/c2)=1/0.6=1.66(6) Relativistic Doppler effect √((1 + β) / (1 - β)) = 3 My question...

Question: Suppose I want to measure the polarity of a photon. What is the minimum amount of energy I need to invest? What are the needed forms? (Examples might include rest mass for storage devices, energy in interacting particles, etc.) I'm looking for an ideal device. Background: I have a...

I apologize if this is ill defined or overly speculative. As far as we know, mass is a permanent characteric of all particles, so we have three disjoint possible categories of particles: bradyons (particles with timelike world-lines), luxons (lightlike world-lines), and tachyons (spacelike)...

What blue shift of distant light would you observe, while free falling into a black hole. It seems that hovering at the horizon (which is not possible), would result in infinite blue shift. But what about the observed blue shift in free fall, as a function of the radial Schwarzschild coordinate?

Apologies if this is in a FAQ somewhere. A is out in deep space. B is falling toward the planet. Does A need both SR & GR to calculate B's time/space dilation as determine by A's IRF?

Let's say we are working with the Schwarzschild metric and we have an emitter of light falling into a Schwarzschild black hole. Suppose we define the quantity u=t- v where dv/dr= 1/(1-r_{s}/r) where r_s is the Schwarzschild radius. What is the u as observed by the emitter? I just need a...

When designing a State Observer for a control system the observer poles (eig(A-LC)) should typically be about 10 times faster than the controller poles (eig(A-BK)). But when designing a digital control system what does it mean for the poles to be faster? For the analog case it simply means...

I am not a theoretical physicist but I have heard of Schrodinger's cat. It is a fact that stresses and strains measured along a structure are directional i.e the stresses and strains vary according to the direction you orient your strain gauge in. Does this have any connection with the 'observer...

If Galaxy A drifts apart from Galaxy B with twice the speed of light then how could a Galaxy C next to Galaxy A drift apart from Galaxy A at a similar speed? edit: PS. Wouldn't that need some kind of "universal central observer" to limit Galaxy A from Galaxy C to not drift apart by more than 2*c?

According to the Schwarzschild metric an interval of proper time d\tau at a fixed distance r from an object of mass M is related to an interval of co-ordinate time dt measured by a distant observer: d\tau = dt \sqrt{1 - \frac{2GM}{rc^2}} This is just the gravitational time dilation formula...

Homework Statement A shuttle is orbitting around the Earth at a velocity of (7.7x10^3) m/sec. The distance between a point on the Earth to the shuttle is (6.7x10^6)m. Calculate the speed of the shuttle relative to an observer on the earth. Completely lost! I was able to solve the...

http://www.ctvnews.ca/world/un-recognizes-palestine-as-non-member-observer-state-1.1058351 I am honestly curious how this is detrimental to peace in the region. I don't really see any downside to this. Anybody care to enlighten me?

In relativity, we do not talk about just space anymore, but space-time, with time being just another dimension. An observer A at rest in an IRF who considers himself at rest at t=0 x=0, has a far away clock at t=100 for example moving towards him, i would like to say at 1second per second, but...

Using a simplified (radial co-ord only, spatially flat) FRW metric with the usual co-ordinates of cosmological time t and co-moving radial distance r: ds^2 = -c^2 dt^2 + a(t) dr^2 we find the path a lightbeam takes by setting ds=0 to obtain \frac{dr}{dt} = \frac{c}{a(t)} Therefore if a...

What is the time measured by an observer who is in free-fall near an object? The Schwarzschild metric is given by: \large c^2 d\tau^2 = (1 - \frac{r_s}{r}) c^2 dt^2 - ( 1 - \frac{r_s}{r})^{-1} dr^2 - r^2(d\theta^2 + \sin^2 \theta d\phi^2) Now for an observer at a fixed position one uses...

Homework Statement A train is passing a platform at 0.75c, and an observer, stationary and at the middle of the platform, sees two bolts of lightning simultaneously hit the front and back of the train when the train's middle was adjacent to the middle of the platform. A passenger on the train...

On 2 October, 5 days from now, Derek Wise will give an online international seminar talk which will be a followup to his June 2012 paper with Stefen Gielen---as I recall a lot of us found that paper very interesting and it topped the second quarter MIP poll. So I want to review that paper, the...

for an observer arriving at a random time t_1, where t=0 is the time when the last car passed, i got the following pdf for Δ^∗- the time the observe waits until the next car: ρ_{Δ^∗}=\frac{1}{Δ^∗}⋅(e^{-\frac{Δ^∗}{τ}}−e^{-\frac{2Δ^∗}{τ}}). the mean is τ, like the book said and it goes to 0 for...

I know this is a stupid question but I can't figure out how to get an answer. I'm trying to figure out if the rules of relativity force a limit on the velocities of two objects in relation to each other. Just as a thought experiment, if a spaceship is traveling at 186,281 miles per second over a...

Practicing Lorentz transformations but still not absolutely clear about conditions for observer's frame of reference. For example: Suppose that just as one of Einstein's long and surreally fast trains is passing a station platform, lightning strikes the platform at two points making scorch...

It is said that in the case of a homogeneous and isotropic spacetime, the surfaces of homogeneity must be orthogonal to the tangents to the world lines of the isotropic observer. Does this mean that the isotropic observers are always at rest in a surface of homogeneity?

I know very little about QM, so forgive me if this question is a bit difficult to comprehend. I understand that there is some debate about whether a conscious observer is necessary to collapse the wave function. But I was wondering if there was any experimental evidence showing to what degree a...

Is it safe to conclude from the double slit experiment that the observer actually affects what is being observed? I ask with regards to a project I'm writing which I wish to be scientifically accurate.

If he can do only one thing at a time, so how is it possible for him to think on any thing. That is events are thought to happen in a series of freeze-frames. Or to say an observer has to be separate from these freeze-frame, to make thinking possible. Also how is the observer separate...

Spacetime curvature observer and/or coordinate dependent? In another topic several people suggested that spacetime curvature is not absolute, it apparently depends on the observer and/or coordinate system. Apparently if someone goes fast (whatever that might mean in relativity) curvature is...

It is known since Hawking that an observer "a rest" at some far distance of a black hole sees a thermal radiation emitted by the black hole. The mass of the black hole diminishes while it emmits the thermal flow of particles. For a free falling observer there is no thermal radiation. So, for...

Couple noob questions. 1.What is quantum mechanical definition of an observer? 2.Why is looking at the double slit experiment with your eyes while the electron goes through any different than a camera looking? Each one is looking, one can just see better. Is it the fact that the outcome...

Is there a region that the light never reaches the 'uniformly accelerated' observer? Of course, light travels in the same direction the observer moves. It sounds weird for me... I derive the parameterization of t and x, and gets hyperbola. So I try to find with drawing that in the ST...