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Questions tagged [observers]

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5
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1answer
505 views

What happens to objects sucked into a black hole after the black hole evaporates away?

Suppose an object falls into a black hole that's so massive that it wouldn't get torn apart at the event horizon. What happens to it after the black hole evaporates away? According to the theory ...
3
votes
1answer
357 views

Video of Double Slit Experiment Observer Effect

I have been watching a lot of videos of the double slit experiment and trying to wrap my head around it. I found examples of where the experiment has been done, however the videos cut out and only ...
2
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1answer
95 views

In special relativity, is there a prescription to find the coordinate transformation to a general (for instance accelerated) observer? And in GR?

Suppose we are in an inertial frame, so that the metric in our coordinates is just the Minkowski metric, \begin{align} \text{d}s^2 = -\text{d}t^2 + \text{d}x^2 + \text{d}y^2 + \text{d}z^2. \end{align} ...
2
votes
1answer
117 views

Operational Definition of Reference Frame in General Relativity

Most treatments of GR begin with the assumption that spacetime is a pseudo-Riemannian manifold (or, sometimes, that it is a more general manifold). But this entails quite a few tacit assumptions about ...
2
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1answer
347 views

Does a complete theory of quantum gravity require anthropic post-selection?

Does a complete theory of quantum gravity require anthropic post-selection? Certainly the black hole complimentarity and causal patch conjectures highlights the essential role of observers, at least ...
1
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1answer
71 views

Einstein's Simultaneous Lighning and the Lorentz Transformation

I am reading Einstein's book, "Relativity: the Special and General Theory" translated by Robert W. Lawson, and I have some questions concerning Special Relativity -- specifically, the thought ...
1
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1answer
76 views

How does a distant observer see matters that “form” an initial black hole?

I did see Can black holes form in a finite amount of time? but it does not seem to discuss how a distant observer would see evolution of collapsing matters that form a black hole. Does it view these ...
1
vote
1answer
158 views

Special Relativity pothole paradox

Consider a man who is 1 metre in width and is running (at relativistic speeds) towards a pothole in the ground which is also 1 meter in width. In the reference frame of the man it appears as though ...
1
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1answer
157 views

Does curved spacetime arise from inhomogeneity of gravitational field?

In general relativity textbooks such as Sean Carroll's Spacetime and Geometry, there is often a line of reasoning that goes like this: Strong equivalence principle states that free falling frames are ...
0
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1answer
39 views

Interdependence of time, the speed of light and distance in General Relativity

In the relation $$ \text{time}\cdot\text{speed of light} = \text{distance}\,,$$ by definition, the speed of light is constant. When bringing a clock, like in a GPS satellite, up into orbit, i.e. ...
0
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1answer
34 views

Reference when measuring the speed of fast moving objects

Let's assume an object is moving at a speed of V=50% of the speed of light, so the time in the frame of this moving object becomes slower by an amount of X. when we say time becomes slower by, it ...
0
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1answer
119 views

Question on Painlevé Gullstrand coordinates

A known set of coordinates used for the Schwarzschild metric is the Painlevé-Gullstrand coordinates. They consist in performing a change from coordinate time $t$ to the proper time $T$ of radially ...
0
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1answer
66 views

What (if any) significance exists in the analogy between the speed of light limit and the Schwartzchild radius of a black hole

I have always been intrigued by what seems to be very similar characteristic of the phenomena of traveling very, very fast, (close to the speed of light , and the Schwartzchild radius. AS a body gets ...
0
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1answer
63 views

Do multi-state of entangled particles exists?

I haven't taken any course in Quantum mechanics. But I felt "Quantum Entanglement" quite interesting. I recently read some articles on it. But I am not sure if I understood anything or satisfied with ...
0
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1answer
47 views

Force seen by an observer traveling near the speed of light

Suppose there is a wind with velocity $v \ll c$, which is blowing on a person who is moving at velocity $u \ll c$ (both in the $x$-direction). In the rest frame of the person, the wind exerts a force $...
0
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1answer
110 views

Help me to understand how time is relative!

I'm a bit confused about how time can be relative. Example: if a cosmic event happened that could be observed from earth, multiple times, because light from this event reached earth at different times ...
0
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1answer
139 views

Are quantum measurement of a system only occurring with human interaction?

In quantum physics, any functional interaction like measurement/observation forces particles down to a single state. Yet when plants do their photosynthesis it's been discovered that they actual ...
0
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1answer
34 views

Teleportation and the observers effect

I'm a layman, and I was wondering, if teleportation is to ever exist, I'd assume it'd be in the sense that you would take the object you are trying to teleport, get it's exact makeup, then send that ...
0
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1answer
145 views

To an observer in a black hole, would light be stationary? Would it be as if the black hole is accelerating faster than the speed of light?

Taking into account that we know that gravity and acceleration are fundamentally indistinguishable from each other, Would an observer in a black hole believe that he's accelerating upwards faster than ...
0
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1answer
115 views

Velocity in different time frames

A satellite orbiting the earth experiences time faster than a person on earth as its in a weaker gravitational field (which has a greater effect than the slowing down of time caused by its motion) ...
0
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1answer
156 views

Can the fact that the vacuum energy in curved spacetime is not boost invariant be explained without mathematics?

I read in an answer to a question if Hawking radiation can be explained without too much mathematics that this is impossible insofar the vacuum energy is not boost invariant in a curved spacetime. ...
0
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1answer
86 views

Twin Paradox From Neutral observers perspective

Suppose two planets A & B, with B moving away from A at velocity v. A spaceship departs from A in the direction of B at velocity v (putting it in the same inertial frame as B), and remains that ...
0
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1answer
57 views

Could we recognise if time was running at a different rate for one species than another? I.e a human and an ant

My question is quite simple if time ran at a different speed for smaller creatures, how would we be able to observe this or confirm by experiment?
6
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0answers
99 views

Twin paradox with one twin in orbit, one in radial free-fall

Many questions on Physics SE relate to the twin paradox, but I did not find any that ask this specific question. Suppose that object A is in a circular orbit around a spherically symmetric, non-...
4
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0answers
98 views

Role of the observer in Gödel's universe

I am here to clarify myself about the role of the observer in Gödel's solution (1949) of Einstein's field equations. The Universe we are dealing with is anisotropic, since the axis of rotation ...
2
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0answers
70 views

Could you actually see the event horizon of a Black Hole?

For years I thought to myself that surely you'd be able to see the event horizon of a Black Hole when looking at it against the surrounding light. I thought that it would be similar to this: Where ...
2
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0answers
47 views

Centre of mass in General Relativity

In the paper from Costa 2014, Figure 1, it discusses how the velocity of an observer influences where the center of mass of a spinning object is measured. If an observer is moving with velocity $v$ ...
2
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0answers
52 views

Gravitational time dilation and the pace of time

If we are in empty space far from a black hole, at rest relative to the hole, we would look at a clock and a light source inside the gravitational field of the hole, then we would, according to the ...
2
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0answers
186 views

Does an object travelling at speeds approaching $c$ observe an increase in the expansion rate of the universe?

According to the theory of special relativity as an object approaches light speed it experiences length contraction. This means that the distance it observes between it and it's destination reduces as ...
2
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0answers
296 views

Observers in (Schwarzschild-) de Sitter spacetime

In (pure) de Sitter spacetime, the cosmological horizon is said to be ‘observer dependent’. I imagine that as the observer always being in the center of that horizon. Another (spacelike separated) ...
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0answers
49 views

Apparent FTL speeds seen by observer

MY guestion is if I was in a ship orbiting a black hole (not very close to the event horizon) I am orbiting pretty far and I am experiencing that my time is slowing down realitive to people on earth. ...
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0answers
36 views

Entropy and observers

Struggling to understand the stance Bousso takes in his paper, The Entropic Landscape, https://arxiv.org/abs/1001.1155 Is he saying that because only by observing an increase in available state we ...
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0answers
199 views

Why is the double slit experiment highly regarded as mysterious?

I read in Wikipedia: The need for the "observer" to be conscious has been rejected by mainstream science as a misconception rooted in a poor understanding of the quantum wave function ψ and the ...
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0answers
76 views

Indeterminacy in Quantum Mechanics

Heisenberg's uncertainty principle tells us that there is a lower limit on the accuracy with which we can determine both the momentum and the position of a particle simultaneously. $\Delta$$x$ $\...
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0answers
102 views

Special Relativity

Does special relativity require faster than light information transfer to verify length contraction and time dilation? How does the "outside observer" measure these variables? I guess the outside ...
1
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0answers
65 views

Can two entangled electrons can get disentagled in Nature, withous us making a measurement?

Imagine we have two free, entangled [by their spins, which are in this case non-separable, while $x$ (or $p$) electrons are clearly separable]. In an experimental setup, we can measure (and observe) ...
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0answers
280 views

Question about some of the science in “Passengers”

In the movie "Passengers", there is a spaceship that is moving at half of the speed of light towards a destination planet orbiting another star, and the story takes place about 30 years after the ...
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0answers
77 views

single Observer iterpretation, experiment design

I am thinking of an interpretation of QM in which there is a single Observer (O). That is, its mind's history is marking a special path on the many-world graph, which we identify with reality. This ...
1
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0answers
284 views

How to determine the three-velocity measured by a single observer?

In this question the issue of extracting the three-velocity of a test particle in some frame arose. The answer provided by @PaulT and in this paper (arXiv) seems to me to give rise to ambiguity when ...
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0answers
58 views

How does an observer in arbitrary state of motion assign numbers to events in a flat spacetime?

In a flat spacetime, there is an inertial observer, who assigns events coordinates in a usual fashion: Placing a clock everywhere and synchronize them. From his POV, the other observer is moving in ...
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0answers
367 views

Why are subjects upside down when I look through my door peephole?

There is a convex lens 3/4" on the outside and 1 1/2" convex lens on the inside. Each lens has one flat side facing out and one convex side facing in. What can be done to correct this image?
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0answers
50 views

Does absolute motion/stillness exist?

I am not a physicist :) I (think I) understand the idea that motion can be relative in the sense that, I'm standing still inside a moving train in regards to the moving train itself, but I'm moving ...
0
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0answers
37 views

Equivalence in all inertial frames

Suppose there is a train moving to the right. and inside the train there is an observer, A. Outside the track, there is another observer B. When the train passes in front of B, right at the instant ...
0
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0answers
64 views

Observers and traveling backwards in time in Godel's universe, Is it possible?

Once we choose a position in Godel's universe, there is a cylinder associated to our position which divide our spacetime into two separated regions and in this coordinate system, our cylinder have a ...
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0answers
45 views

Is there an observer dependent temperature everywhere in spacetime?

A temperature $T=\dfrac{\hbar a}{2\pi c k_B}$ is associated to an uniformly accelerated observer. He feels this temperature all along his trajectory. The inertial observer will not assign this ...
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0answers
30 views

Is the Hubble parameter different for each observer?

As the universe expands, galaxies disappear beyond the observable universe. So we could calculate the rate of expansion of the universe (the Hubble parameter) by estimating the rate of disappearance. ...
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0answers
111 views

Energy per unit mass in General Relativity

The Schwartzschild metric in standard coordinates with signature $(1,-1,-1,-1)$ is given by $$ds^2=(1-\frac{r_s}{r})\ dt^2 - (1-\frac{r_s}{r})^{-1}\ dr^2 - r^2(d\theta^2+\sin^2\theta\ d\phi^2).$$ As ...
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0answers
66 views

Speed of light, comparison of two light waves travelling side by side

okay so.here is setup of my question...say we have two observers A and A'..A is fixed to origin of coordinate axis x,y while A' is inside a hollow box (shown as rectangle MNRP) whose one side MN has ...
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0answers
94 views

Is it possible to derive the Doppler effect formulas for sound using relative velocity?

Is it possible to derive the Doppler effect formulas for sound using relative velocity? If possible can anyone please explain it to me.
0
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0answers
171 views

does an object travelling close to the speed of light in an inertial frame of reference behave Relativistically

The two tenants of Special Relativity are: The laws of physics are the same in all inertial frames of reference. The speed of light in free space has the same value $c$ in all inertial frames of ...