The observer tag has no wiki summary.
131
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14answers
42k views
A mirror flips left and right, but not up and down
Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
15
votes
8answers
2k views
How can anything ever fall into a black hole as seen from an outside observer?
The event horizon of a black hole is where gravity is such that not even light can escape. This is also the point I understand that according to Einstein time dilation will be infinite for a ...
12
votes
2answers
279 views
What does a sphere moving close to the speed of light look like?
What shape does the viewer in a reference frame with $v=0$ perceive? I suppose that since the sphere moves in one direction only (oX only, not oY) its section would change into an ellipse, where the ...
10
votes
13answers
1k views
What are the mechanics by which Time Dilation and Length Contraction occur?
What are the mechanics of time dilation and length contraction? Going beyond the mathematical equations involving light and the "speed limit of the universe", what is observed is merely a phenomenon ...
9
votes
2answers
208 views
Is the uncertainty principle just saying something about what an observer can know or is it a fundamental property of nature?
I ask this question because I have read two different quotes on the uncertainty principle that don't seem to match very well. There are similar questions around here but I would like an explanation ...
8
votes
5answers
571 views
Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?
From what I understand, the uncertainty principle states that there is a fundamental natural limit to how accurately we can measure velocity and momentum at the same time. It's not a limit on ...
6
votes
8answers
2k views
Would time freeze if you can travel at the speed of light?
I read with interest about Einstein's Theory of Relativity and his proposition about the speed of light being the speed limit for anything with mass. So, if I were ...
4
votes
5answers
503 views
Time Dilation - How does it know which Frame of Reference to age slower?
Okay, I'm asking a question similar to this one here: Time Dilation - what happens when you bring the observers back together?. Specifically, I am curious about a specific angle on the second part of ...
4
votes
3answers
197 views
Subjectivity of decoherence
I read that quantum decoherence is subjective, in the sense that two observers may not have the same "environment" and after each one has traced over those degrees of freedom they will end up with a ...
4
votes
2answers
607 views
How can time be relative?
I don't understand how time can be relative to different observers, and I think my confusion is around how I understand what time is.
I have always been told (and thought) that time is basically a ...
4
votes
3answers
182 views
Black hole formation as seen by a distant observer [duplicate]
Possible Duplicate:
How can anything ever fall into a black hole as seen from an outside observer?
Is black hole formation observable for a distant observer in finite amount of time? ...
4
votes
1answer
57 views
Relativity of simultaneity - An example
I am trying to understand the relativity of simultaneity in different frames, and I am trying to work out an example.
Suppose along the x-axis there are two points 2000m apart. Event A happens at t=0 ...
4
votes
2answers
131 views
Effect of gravity at near-lightspeeds
Let's say I'm in a space station, hurtling towards our galaxy nearly close to the speed of light. From my reference frame, I see the galaxy coming towards my ship at the same speed.
I pass the Sun, ...
4
votes
1answer
193 views
Falling into a black hole
I've heard it mentioned many times that "nothing special" happens for an infalling observer who crosses the event horizon of a black hole, but I've never been completely satisfied with that statement. ...
3
votes
2answers
213 views
What do you feel when crossing the event horizon?
I have heard the claim over and over that you won't feel anything when crossing the event horizon as the curvature is not very large. But the fundamental fact remains that information cannot pass ...
3
votes
2answers
211 views
Decoherence when no one is looking?
I understand that in the single-electron-at-a-time double slit experiment, if a detector is placed before the slit, the interference pattern vanishes.
Suppose I left the detector on, but put a bag ...
3
votes
1answer
135 views
Formation of a black hole and Hawking radiation
From the perspective of an outside observer it takes infinitely long for the black hole to form.
But if the black hole is no extremal black hole, it emits Hawking radiation.
So the outside observer ...
2
votes
5answers
4k views
Why can I never see any stars in the night sky?
I have always lived near a large city. There is a stark contrast between the picture linked below for example, and what I see with the naked eye.
Sometimes I can see a few stars here and there, but ...
2
votes
3answers
182 views
If time slows down when you move faster, does this give you an “effective speed” different from your proper speed?
Suppose you're travelling at 0.9c toward the sun, and you tag past the Earth and start a clock. Would Lorentz contraction/time dilation cause you to get to the sun faster than (about) 9 minutes ...
2
votes
1answer
223 views
What happens to speed and frequency of a light beam moving in transparent medium when observed from different inertial frame of reference?
Suppose a transparent medium where speed of light is $c/n$, an inertial frame of reference $K$ which is stationary relatively to the medium and an inertial frame of reference $K'$ which is moving ...
2
votes
1answer
59 views
An infalling object in a black hole looks “paused” for a far away observer, for how long?
As I understand, to an observer well outside a black hole, anything going towards it will appear to slow down, and eventually come to a halt, never even touching the event horizon.
What happens if ...
2
votes
1answer
105 views
Would dense matter around a black hole event horizon eventually form a secondary black hole? [duplicate]
Possible Duplicate:
Black hole formation as seen by a distant observer
Given that matter can never cross the event horizon of a black hole (from an external observer point of view), if a ...
2
votes
1answer
252 views
Time dilation - why the observers see each other the slow one but then one of them is older or younger?
I'm in trouble with time dilation:
Suppose that there's two people on the Earth (A,B), they are twins and each other has a clock. (So they are at the same reference frame). B travels in a spaceship ...
2
votes
1answer
60 views
Does the observer or the camera collapse the wave function in the double slit experiment?
Ok so if we setup a camera before the slit we will find a single photon and will follow through accordingly, likewise by having a camera setup after the slit, we can retroactivly collapse the wave ...
2
votes
1answer
256 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 ...
2
votes
4answers
148 views
What counts as an observer and memory states in quantum interpretations?
The Everett interpretation has memory robots. Copenhagen requires observer memory states. Consistent histories has its IGUSes. Decoherence has its existential interpretation. All of them refer to ...
1
vote
4answers
176 views
What is the exact mechanism by which time dilates?
What is the exact mechanism by which time dilates for a fast moving object?
Can the time dilation be explained by any theory other than relativity?
1
vote
1answer
217 views
In general relativity (GR), does time stop at the event horizon or in the central singularity of a black hole?
I was reading through this question on time and big bang, and @John Rennie's answer surprised me.
In the immediate environment of a black hole, where does time stop ticking if one were to follow a ...
1
vote
3answers
89 views
Special Relativity - speed of light question
Just a basic question:
I know that if you are traveling at $x$ speed the time will pass for you slower than to an observer that is relatively stopped. That's all just because a photon released at the ...
1
vote
1answer
171 views
Does the increase of (relativistic) mass, while flying near speed of light, has any impact on astronauts? [duplicate]
Possible Duplicate:
Would travelling at relativistic speeds have any impact on human biology?
I am asking myself this question for a few day. What is the answer on: Does the increase of ...
1
vote
4answers
412 views
Questions on wave-particle duality
Wave-particle duality states that a particle has both wave properties and particle properties when one is not observing it.
1) What is an observer? Need it be anything living or can other particles ...
1
vote
1answer
141 views
How does a strobe lamp stop a fast moving object?
A strobe lamp can be used to seemingly stop a fast moving object when calibrated.
Commonly used in quality assurance during production to inspect otherwise non-observable assembly line activity.
What ...
1
vote
1answer
53 views
Does non-mass-energy generate a gravitational field?
At a very basic level I know that gravity isn't generated by mass but rather the stress-energy tensor and when I wave my hands a lot it seems like that implies that energy in $E^2 = (pc)^2 + (mc^2)^2$ ...
1
vote
2answers
161 views
Do scientists literally believe the Schröedinger's cat though experiment?
I've heard the Schrödinger's cat "paradox" (although there's nothing particularly paradoxical about it, just counterintuitive), but I've never been clear on whether or not it's meant to be taken with ...
1
vote
1answer
194 views
What is the speed for an object that travel close to the speed of light?
I have some questions regarding Einsteins theory of Relativity that should be fairly easy to answer. Lets say we make an experiment where we have a rocket (with an astronaut inside) that travels very ...
1
vote
1answer
63 views
How do we know space is expanding when we are part of space? [duplicate]
From what I understand space itself is expanding, and the Big Bang attempts to describe this expansion at the very early stages of the universe.
This is usually described in a visual way as 2 dots on ...
0
votes
1answer
334 views
How does time dilation work without a privileged reference frame?
As I understand special relativity, light travels at the same speed in all reference frames.
What I fail to understand is why time dilation would occur in one reference frame, but not by an equal ...
0
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2answers
201 views
Am I faster than my shadow?
I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?
0
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1answer
106 views
What is the maximum time dilation between two objects, if one is standing still and the other is moving at $c$?
What is the maximum ratio in the rate of change in time in reference to object $A$ which is standing still and object $B$ which is moving at the speed of light?
0
votes
3answers
149 views
Time slowing down problem
When someone moves, time slows down for him. Let, a man standing still and another moving very very very fast, this happens for an hour (as measured by the standing man). Time has moved slower for the ...
0
votes
3answers
109 views
Stuff can't go at the speed of light - in relation to what? [duplicate]
We all know that stuff can't go faster than the speed of light - it's length becomes negative and all kinds of weird stuff happens.
However, this is in relation to what? If two objects, each moving ...
0
votes
1answer
135 views
Does photon possesses no time to cover any arbitrary distance?
Photon travel 8 minutes (with speed $c$) from the sun to reach the earth. Any particle (or space-ship) with velocity $0.99 c$ covers the same distance (93 millions km) within less than 2 minutes ...
0
votes
4answers
202 views
The bigger the mass, the more time slows down. Why is this?
If I were to stand by a pyramid, which weighs about 20 million tons, I would slow down by a trillion million million million of second. Don't know if that's exactly right, but you get the point. Also, ...
0
votes
1answer
151 views
What is the difference between observer, frame of reference, and gauge?
It seems to me that there is considerable relationship between the three concepts: frame of reference, observer, and gauge. How do they overlap?
My current understanding is that an observer with a ...
0
votes
2answers
104 views
Why is matter drawn into a black hole condensed into a single point within the singularity? [duplicate]
Possible Duplicate:
Why is matter drawn into a black hole not condensed into a single point within the singularity?
When we speak of black holes and their associated singularity, why is ...
0
votes
1answer
132 views
In What Frame of Reference does the Special Theory of Relativity Operate? [duplicate]
Possible Duplicate:
Time Dilation - How does it know which Frame of Reference to age slower?
This has bugged me for years.
According to the theory of relativity, the faster an object ...
0
votes
3answers
87 views
Observer effect, do this mean literally someone or just any interaction with other matter?
I am a layman and was wondering, the quantum observer effect. The regular notion to laymen seems to be literally "if you look at it", but as I am coming to understand the world I live in better I feel ...
0
votes
1answer
45 views
Wavefront emitted by bodies at traveling near the velocity of light
I studied that no body can travel with the velocity of light. But, assuming that when a body moves nearly velocity of light, will it obey length contraction law of Einstein or will it emit the same ...
0
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0answers
52 views
What is an “observer” really? [duplicate]
Possible Duplicate:
What is an observer in quantum mechanics?
I'm sick of quantum physics explanations which term experiments where the outcome depends on "if you observe it or not". For ...
0
votes
0answers
36 views
Can a black hole actually grow, from the point of view of a distant observer? [duplicate]
Possible Duplicate:
Black hole formation as seen by a distant observer
I've read in several places that from the PoV of a distant observer it will take an infinite amount of time for new ...
