Observer Definition and 324 Threads

Caveats: I'm sure this is kind of putting the cart before the horse here, because if I have to ask this question, it surely means I ought to be reading up on it first. This is for a story, but that should not mean this is the wrong forum; I'm really just asking about the basics of Minkowski...

So for example, we can say a stationary observer and a moving ship are in relative motion horizontally and at rest with each other vertically, right? This is basic Pythagorean math. Stationary observer has own light clock that dribles up-down like a pendulum and it drops a beam 1 light-second...

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...

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

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?

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.

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...

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...

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...

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...

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!

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...

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: $$f_2=\frac{v-0.1v}{v}f_o$$...

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...

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?

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?

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?

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?

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

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...

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...

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...

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...

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...

I have attempted but with no result.

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...

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...

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...

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?

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...

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...

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 -...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

Continue reading...

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}##...

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...

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...

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...