The tag has no wiki summary.

learn more… | top users | synonyms

0
votes
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
1answer
160 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 ...
2
votes
1answer
178 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 ...
0
votes
0answers
41 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 ...
1
vote
1answer
878 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 ...
4
votes
2answers
270 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? ...
14
votes
2answers
546 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 ...
0
votes
2answers
446 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?
3
votes
1answer
162 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 ...
3
votes
2answers
395 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 ...
0
votes
3answers
173 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 ...
2
votes
1answer
601 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 ...
1
vote
1answer
226 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 ...
2
votes
4answers
178 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 ...
5
votes
1answer
303 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. ...
-1
votes
3answers
225 views

Does the Lorentz transformation not apply to light?

Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
1
vote
0answers
130 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?
1
vote
1answer
294 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 ...
2
votes
1answer
304 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 ...
0
votes
1answer
370 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 ...
-1
votes
1answer
285 views

Time dilation at the speed of light

Does a massless particle travelling at the speed on light in a vacuum (c) experience an infinite time dilation effect? i.e. Would the time dilation extend from the perspective of the massless ...
11
votes
6answers
15k 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 ...
0
votes
2answers
132 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 ...
4
votes
2answers
141 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, ...
5
votes
5answers
10k 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 ...
12
votes
5answers
954 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 ...
4
votes
3answers
241 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 ...
6
votes
2answers
2k 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 ...
3
votes
2answers
287 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 ...
1
vote
4answers
693 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 ...
0
votes
1answer
194 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 ...
24
votes
12answers
3k 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 ...
0
votes
2answers
641 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 ...
2
votes
1answer
314 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 ...
12
votes
13answers
2k 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 ...
5
votes
5answers
651 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 ...
11
votes
4answers
863 views

Can black holes form in a finite amount of time?

One thing I know about black holes is that an object gets closer to the event horizon, gravitation time dilation make it move more slower from an outside perspective, so that it looks like it take an ...