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Questions tagged [observers]

The tag has no usage guidance.

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2answers
54 views

Relativity from a basic assumption

Is it possible to derive Lorentz transformations just by assuming that if two spaceships are moving away from each other with a constant speed, it is impossible for them to tell who is moving, even if ...
0
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0answers
33 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

Is there any change in temperature due to special relativity? [duplicate]

Say I am travelling in a spaceship very close to the speed of light. Would there be any change in temperature in the spaceship relative to outside the spaceship? Please explain in detail.
2
votes
2answers
79 views

Is there a connection between the energy distribution and time dilation?

Can anyone please help me understand what is descibed bellow? Scenario 1. We have a pair of atomic clocks. Let's call them clock A and clock B. We switch both of them on at the same time. Clock A ...
1
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2answers
43 views

How do we observe an electron? [duplicate]

When an electron is observed it acts like a particle and its wave function collapse. This statement is very famous in quantum mechanics, but what is meant by observing an electron? Which devices are ...
1
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0answers
45 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. ...
31
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11answers
7k views

How could quantum effects occur in the early universe without an observer?

In inflationary cosmology, primordial quantum fluctuations in the process of inflation are considered responsible for the asymmetry and lumpiness of the universe that was shaped. However, according to ...
1
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2answers
71 views

Double slit experiment record but not look at it

I am having a tough tough stressful week trying to write an article about quantum mechanics. I know there was a question asked the same thing before, but I didn't understand nor I did not want to wake ...
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votes
1answer
69 views

How can I go and also not go faster than light?

Suppose I am in a spaceship. In this spaceship there is also my friend. So my friend and my relative velocity is zero. So no matter how fast my ship goes my friend's velocity relative to me is zero($0$...
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2answers
82 views

Clock in a sealed box at half the speed of light. How would it know it is moving?

Consider a clock enclosed in a sealed box here on earth syncronized with my wrist watch. I send the boxed clock around the galaxy a couple of times at half the speed of light (or the full speed of ...
23
votes
5answers
2k views

What is physically different about a moving vs still object in space?

If I have two asteroids. One dead still in space and one whizzing by at 10,000mph. What is the difference between the two, physically? If I freeze time and look at the two of them - what differences ...
0
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1answer
38 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. ...
2
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1answer
111 views

Proper time vs time

I'm reading about relativity and I thought I understood things clearly about proper time / coordinates until I read the analysis of the Doppler effect. A and B are 2 fixed points, there is a clock in ...
1
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4answers
109 views

How do we determine who is the “observer” when calculating time dilation? [duplicate]

I was reading about time dilation and I thought of a question. I really think that I am just misunderstanding something, so please bare with the question. But, I would appreciate if somebody could ...
3
votes
1answer
41 views

Bekenstein Bound and frame of reference

According to Wikipedia, this is the formula for the Bekenstein bound $$ S \le \frac{2\pi k RE}{\hbar c}$$ where $E$ is the total mass-energy. That seems to imply that the presence of a black hole in ...
1
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0answers
63 views

Can matter actually cross the event horizon effectively falling into a Black hole? [duplicate]

The answers I have seen do not take into effect the growth of the radius of the event horizon as significant amounts of matter get close to the existing event horizon. I would have expected that ...
2
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0answers
71 views

Problem in Special Relativity [closed]

"A space probe is sent to the vicinity of star Capella, which is $D = 42.2 \ light \ years $ from earth. The probe travels with a speed of 0.9930c. An astronaut recruit on board is 19 years old when ...
6
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0answers
90 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-...
1
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2answers
104 views

What does it actually mean to say that time “speeds up” or “slows down”?

I was thinking lately about relativistic time dilation and time passing differently on other planets (which both, eventually turned out to be caused by the same principle). Now, quite naturally (as ...
0
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1answer
50 views

Are black holes totally black and formed? [duplicate]

Good morning, I know some similar questions have been asked but I don't find a convincing answer in these. Excuse me if I have missed the answer. My question is: I have learned that some black holes ...
0
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3answers
89 views

Observer in Many Worlds Interpretation [duplicate]

Something has been bothering me about the Many Worlds Interpretation. Proponents of it (e.g. Sean Carroll) often claim that it does away with the observer, or at least the paradox-inducing status the ...
2
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0answers
23 views

Black Hole Formation Physics [duplicate]

Considering only Black Holes that form due to gravitational collapse since the big-bang, wouldn't it be true that that have not (in our reference frame), in fact, formed a singularity or even much of ...
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0answers
44 views

If I walk and you stand still, do you get older than me faster?

I was watching a video from Aurelien Barrau about relativity and time. As he was talking to the audience, he said that since he was walking on stage, he was ageing slower than people sitting in the ...
0
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0answers
31 views

How can our universe have black holes? [duplicate]

Assuming that we were never inside a blackhole at any point in the history of the universe, how can blackholes exist against Gravitational time dilation? For any point in space time in the known ...
1
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0answers
34 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 ...
2
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2answers
66 views

Is it possible to speed up time using Special Relativity?

I know that with special relativity when having more velocity than a stationary observer your time relative to the observer slows down. Is it possible using special relativity to increase your time ...
1
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2answers
86 views

Minimum separation from the spacetime interval

I've been working through invariant spacetime interval questions recently, and I came across a question in my lecture notes where; $$\Delta s^2=\Delta x^2 -(c\Delta t)^2 > 0 $$ Now it is clear to ...
1
vote
2answers
87 views

If the speed of light is a limit, is there a way to tell which direction we are moving through space and how fast?

Say two photons start at point A, and go in opposite directions. They will be traveling apart at 2x the speed of light correct? So if this limit is how fast you are able to travel through space (and ...
0
votes
1answer
59 views

Why the speed of light is independent of the relative motion of observer? [duplicate]

As we use Lorentz transformation equation to relate velocity of particle measured by observer which is in frame s this frame is in relative motion having some velocity to that particle so Why the ...
3
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5answers
143 views

Is relativity really relative?

Because of the relativity of linear motion, you can't tell the difference between whether your spaceship is moving and the stars are standing still or whether you're still and the stars are moving the ...
9
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4answers
821 views

Twin paradox in curved space time [duplicate]

In a flat space, where special relativity works, a travelling body can only return to the same point if we apply some kind of acceleration to the body. So twin paradox is not a paradox because a ...
1
vote
2answers
83 views

Doesn't the slowing of time when travelling at almost light speed create a paradox with an observer? [duplicate]

Disclaimer: I am extremely new to this and have no proper knowledge of this subject at all, this is just an idea that I had which I want to properly understand. I don't have any knowledge of necessary ...
9
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3answers
3k views

Which observer measures proper time in the twins paradox?

I know that proper time is defined as the time which the clock moving relative to that observe shows. That is, a clock attached to observer A will always be As proper time. I also understand that this ...
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2answers
42 views

How to calculate distance of earth when observer in space ship which travel with speed of light

Suppose we have two observer one is on earth and other is in space ship. If we launch the space craft and a light ray at the same time from earth, after 1 minute, what will be total distance travelled ...
5
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2answers
99 views

Would a Schwarzschild black hole “appear” to be a sphere in all reference frames?

I am wondering if all observers would agree that a non-rotating, non-charged black hole is spherical (i.e. there is no reference frame where one would measure it to be oblong in one dimension). I ...
1
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2answers
95 views

Rindler Coordinates and homogeneous Gravity Field

I understood from the equivalence principle that an accelerated observer in free space is equivalent to a stationary observer in a gravitational field. As far as I understood further, this means to ...
0
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1answer
67 views

What is an “observer” in quantum mechanics? [duplicate]

i read about the electrons double slit experiment, when both slits are open, electrons will form an interference pattern, but when there is a detector put to "observe" this weird behaviour, the ...
0
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2answers
71 views

If we filmed what happens on an extremely time dilated planet in realtime

Say there was a planet that experienced insane time dilation due to orbiting a black hole, say 1hr on there is 7 years on Earth (something like that), and that it was close enough to Earth for light ...
1
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2answers
134 views

Do you see the outside world from inside the black hole (can you see past the horizon from inside it)? [duplicate]

I have read these questions: If you fall in a black hole, when do you go past the event horizon? Can matter really fall through an event horizon? How can anything ever fall into a black hole as ...
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6answers
217 views

Is the relative speed of light really invariant, irrespective of the motion of the observer? [closed]

If 3 observers are on a planet which 100 light years from a star, and the star goes supernova, if one observer moves towards the star and one moves in the opposite direction, each observer will see ...
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2answers
65 views

Does the position in universe of a person not matter regarding death?

I might be completely wrong, but watching a documentary about time, the Einstein theory of relativity came up. From their explanation, time "slows down" depending where you are in the universe. I ...
2
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2answers
145 views

Can the horizon of a black hole move?

Because of time dilation we cannot observe a black hole forming in a finite amount of time. For the same reason I suppose we also cannot observe the horizon moving: everything happening on the horizon ...
1
vote
1answer
52 views

Doppler effect in light (Observer moving away from source)

I understand this intuitively and can picture it in my head, but when I do it on paper, the result is a sign difference that I cannot understand According to this diagram the wavelength = ct-vt = t(c-...
0
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2answers
51 views

Clearing up a discrepancy when deriving the Lorentz transformation from length contraction

I've been working through the Feynman Lectures on Physics. I'm currently on lecture 15: The Special Theory of Relativity, specifically 15-5, the section on the deriving the Lorentz Transformation ...
0
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1answer
68 views

Shortening of distances in Relativity Theory

I am studying relativity theory and I have understood why distances become shorter from the perspective of someone who is travelling close to the speed of light. However, later on I read that the ...
2
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1answer
108 views

How is it possible to enter a black hole, given time dilation?

This is a bit of a complex question - example scenario: X and Y (who happen to be immune from radiation and gravitation spaghettification, don't draw this into the equation) are some distance from a ...
4
votes
2answers
172 views

Consequences of infinite redshift in the event horizon of a Schwarzschild black hole

I am familiar with the usual derivation of the fact that it is impossible for someone to observe an object enter a black hole, because of the fact that light gets infinitely redshifted as its source ...
0
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2answers
103 views

The speed of light and the increase of relativistic mass [duplicate]

The speed of light theory predicts that as things travel faster their mass increases, so I think we if we look at a plane accelerating from mach one to mach two and measure the relativistic mass of ...
2
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0answers
60 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 ...
0
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1answer
49 views

Would humans die of old age on an interstellar/intergalactic voyage? [duplicate]

It is often claimed that if we ever sent humans to colonize other stars, we would have to send them on generational ships. However, if the ship traveled at $99.9\cdots 9c$, wouldn't the passangers' ...