Observer Definition and 324 Threads

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...

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...

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...

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...

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...

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...

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?

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...

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

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...

Let’s assume it is 5,000,000 years in the future and we have created a quantum synchronization box that can broadcast a signal, used to synchronize two clocks and video feeds, no matter where they are in the universe. The third observer watches a split TV screen, which features the faces of two...

There are many videos and articles about this topic (what it looks like if you fall into a black hole). I remember hearing that, inside the event horizon of a black hole, time has essentially stopped for an outside observer. However, if you fell into one that would mean that any amount of time...

Can someone or approve or disapprove my question. I want to make sure I get this right. I will use Bill & Nancy as observers and friends For example, if Bob is going at the speed of light inside a spaceship, his mass will increase indefinite but he will not notice the effects. Bob will...

I don't know if you physicist out there knows it, but the statement that observing something changes its state is having a drastic impact on the less informed populace at wide. An example, one of the most popular Quantum Physics video on youtube <Link to video not acceptable under PF rules...

What can be counted as a observer effect? that would cause collapse of the wave function? e.g. Is it only the which path information or is it purely the act of observing? As in if observer effect is the cause of wave function how come we can even see the interference pattern at all, Is it...

I have question that involves quantum tunneling and wave function collapse that occurs when the state of an object is measured. I will try to explain what I mean. We don't know the exact location of an electron in an atom, because it doesn't have a location, it is in its wave form and we can't...

WARNING. I'm not a physicist! If there was a universe that only had 10000 photons and we observed all of them then ran the double slit experiment would we get a normal pattern or an interference pattern? If we observe a particle is that it forever in the universe that we happen to be running...

CASE I - Do magnetic field is felt by observer which is moving and charge is stationary? CASE II- Do magnetic field is felt by observer which is moving with same velocity as that of charge? Does it has some experimental proofs and explanations...

Hey guys and gals, clearly I'm new here, not only new here but new to QM (relatively speaking). I've read a few threads here pertaining to a thought I've been pondering on but the answer doesn't seem clear. In the Copenhagen interpretation, what qualifies as a "measurement", and/or what...

I understand that the coordinate system (CS) for a distant observer Od is different than that for an observer Of who is falling radially toward the event horizon of a non-rotating black hole (BH). Using the Schwarzschild metric, I would like to understand the transformation equations that...

The problem with the notion of Event Horizon is that it speaks ot events which will never be seen in the future. So it requires to wait eternally. So apparent Horizon is introduced. It uses http://www.fysik.su.se/~ingemar/relteori/Emmaslic.pdf They are closed spacelike surfaces. when they emit...

Howdy. It has become clear to me that translational motion is not taken into account in general relativity because it is subjective, and that rotational motion is taken into account in GR in places such as the Kerr Metric. What makes rotational motion so absolute? Couldn't an observer's...

Is it true that for a free falling observer in a non homogeneuos gravitational field, the metric according to his reference frame is always Minkowski? If it is true, Is it valid only locally?

Hello again. In a double slit experiment with electrons, suppose that we have the instrumentation to measure how space-time is curved by these particles. Would it be possible to obtain the electron's position and momentum by measuring the change in the direction of photons that move nearby but...

Hi. From what I've read about the "observer effect" in the two slit experiment, the electron's wave function collapses due to photons altering its momentum. Now, in the beginning of the universe photons couldn't escape the original Big Bang fog until it cleared out, so these should have...

Hello, I signed up cause I was going through the Quantum Eraser threads, but couldn't find an answer to my question. It's about this version from 1999/2000 of the elaboration on the classic double slit experiment: Results seem quite straight forward. Wherever we have "path information" the...

Hello! I've been reading up about Quantum Mechanics, and I'm trying to understand various aspects of the double slit experiment. This is one of among many videos I've watched: Dr Quantum - Double Slit Experiment Here's my understanding so far of the basic setup (where the gun is shooting out...

Homework Statement As you drive at a speed of 15.0 m/s an ambulance approaches you from behind with its siren blaring at a frequency of 1022 Hz. After the ambulance has passed you the signal is now 981 Hz. If both you and the ambulance travel at a constant speed how fast was the ambulance...

Homework Statement Two sound sources 15m apart producing identical 229 Hz sounds. As you move from one to the other, you hear beat frequency of 2.5. How fast are you moving?[/B] Homework Equations The question asks for the velocity of the observer Vo. The trick here is to use the standing wave...

It is said that when an observer look up the sky and observe the cosmos, the further out he looks, the further back in time he sees, allowing him to peer into the past. However, there is a catch, namely, the observation must take place at present time. In other words, a distant object 100 light...

Can I consider each particle as there own observer with there own personal experience of time say each quark or each electron ? Because I read that every observer is as valid as any. I know that general relativity is a theory applied to the very big and here I am asking question for the very...

So if we "look" at a particle, then its wave function collapses. Does "look" mean, hitting that particle with another particle (a light particle?). A simple Yes/No answers first please. I mean, does its wave function collapse because we first need to hit that particle with an electron or a...

Please someone help me! I am suffering from severe depression after seeing philosophical videos (deepak chopra is one of them) about reality. Many of them talking that reality is an illusion and nothing exists, and used quantum physics as a reference (the observer effect). Others simply say the...

Wormholes usually send things through time and space, right? So if an observer threw a baseball through a wormhole, the baseball's position in space-time would change. However, can that action affect the observer's location in space and time, or would it create some sort of paradox?

Hi, I have 16 years old, I am planning to be a physicist in the near future, and I have 3 doubts, could you guys answer to me? 1. Does quantum entanglement proves that everything is connected? http://phys.org/news/2015-01-popper-againbut.html#nRlv 2. 'The Observer Effect' and 'The Uncertainty...

I've recently come across the claim that if the mouths of a hypothetic wormhole don't move in relation to each other, then paradoxes in the form of closed timelike curves cannot be demonstrated to occur, even if an observer moves at relativistic speed relative to them. Is this true? I want to...

Hi guys, in GR a free-falling observer will measure the local speed of light as c, like in SR. My question is will an accelerated (non-inertial) observer locally measure a greater speed than c, or will he also measure the local speed of light as c. For instance, if there is an object that is...

Suppose an observer flies through our solar system at ##v \approx c## relative to the Sun, such that he sees each planet's (and the sun's) mass as greatly increased. What happens to the orbits of the planets? Since he sees the center of mass of the solar system as flying past him at ##v \approx...

Black holes are claimed to radiate at a temperature corresponding to the hawking radiation. But who is measuring the temperature? If the radiation is measured from far away the red shift will indicate a lower temperature won't it? Is the temperature given by the formula as measured from a...

According to the observer effect, a particle changes when observed. Is it possible that how it changes is predetermined at its creation? Are there any papers that have explored this?

Hey, I have a question regarding accelerated motion in special relativity. Suppose an observer has a constant proper acceleration α, his velocity in an inertial frame of a distant observer will then be given v = c tanh(ατ/c), where τ is the proper time of the accelerated observer. Since every...

In case when we don't observe the presence of an electron at either slit, there is an interference pattern, in case we do observe there is a 2 band patter, as an electron would be a particle. I understand that without an observation, the state of an electron in a superposition of all eigen...

A train (source) approaching a stationery observer, wavelength of the sound is equal to the distance between source and observer, How?

We all remember the animations describing the double slit experiment to the public, laying out the foundations of the mysterious quantum world. Now take the part when we try to determine which slit the electron went through. The narrator will say something like this, in a hushed voice: „And...

Homework Statement the observer is stationary , but the sound source is moving towards the observer , i was told that the speed of sound relative to the observer doesn't change. why is it so ? in my opinion, the speed of sound relative to observer changed . because of v= f x (lambda) , as...

If you have two hydrogen atoms as your system, then you use the many body schrodinger equation for 2 protons and 2 electrons. The coulombic repulsion between the two atoms is built into the SWE, so is there a range of different possible magnitudes for the repulsion? If so, does the system decide...

Homework Statement why the wavelength of sound is affected by the moving observer? because as the observer move, the sound source is still stationary . so in my opinion it's not affected by the moving observer. the ans is C for this question. i can't understand. Homework Equations...

According to Einstein (e.g. in his book The Meaning of Relativity), a clock rotating about a central clock will be judged by the central clock to run slower than the central clock. This means that a signal sent by the central clock will be perceived by the rotating clock as being of a higher...

Does mechanical energy of a system depend on the framework of an observer (neglecting a constant)?

I am trying to understand this apparent "paradoxes" but probably i am missing something important. Imagine that accourding to stationary observer on Earth two twin cats are moving in the opposite directions with speed -v and v. When the two cats meet the stationary observer at the beginning O...