Questions tagged [space-time]

Questions regarding the 4-dimensional background structure of our universe.

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1answer
249 views

Can we see Earth by looking into space?

It is known that spacetime is curved,so I am wandering to know if its possible to look into space and we see earth (light from earth long long ago). Did I understood spacetime correctly and if its ...
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1answer
720 views

Does Time Exist for Photons? [closed]

If time slows down the closer you get to the speed of light, does it follow that time does not exist for photons. Do photons - even if they travel across billions of light years of space - arrive at ...
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1answer
98 views

When black holes such as those detected by LIGO merge, in what ways does the Schwarzschild Radius warp?

I was reading the paper about LIGO's detection of gravitational waves, and I wanted to know what the Schwarzschild Radius did. For example, I feel like the simulation here is oversimplified, and that ...
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2answers
259 views

When you travel fast around a black hole, do you experience high speed yourself?

When an object in the space comes close to a massive body (like a black hole or a neutron star), we see from Earth that its speed significantly increases while it is close to the body. As we know, ...
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2answers
827 views

time on earth compared to completely stationary in space

I recently started trying to understand the theory of relativity and I have the following question. Because earth is orbiting the sun at approx 67,000 mph (and its my understanding time slows down ...
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1answer
92 views

Perception of an objects history passing as an observer moves toward it

If a star is 20 light-years away and I look at it through a telescope, what I'm observing is what the star was doing 20 years ago yes? So, if I fix my sight on the star and move toward it (for example'...
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3answers
475 views

Distinction between metric expansion and objects just moving apart from each other?

I see explanations likes this: Galaxies and other sources, then, are not strictly expanding away from each other but rather are attached to the fixed grid on the expanding fabric of spacetime. Thus, ...
4
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2answers
145 views

Center of the universe

Big bang is not an explosion, but an expansion of space and time. Universe had almost infinite density... wait a moment. If it had ALMOST infinite density, it had a certain volume, and thus, space ...
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0answers
60 views

Why does the outside edge of a Kerr black hole ergosphere rotate at the same speed as the inner edge?

Reading through the Wikipedia on a Kerr black hole ergosphere, and this nice question on the maximal spin rate of a black hole leads me to ask: why does the outer edge of the ergosphere rotate at the ...
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1answer
115 views

Einstein General relativity and bending of space [closed]

As Einstein's General relativity suggests that the space time curves in the presence of matter, which is experimentally proven too, this phenomenon also explains orbits. My question is if the ...
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6answers
3k views

If an exoplanet transit we are seeing is 13000 light years away, are we seeing a 13000-year-old orbit? [duplicate]

If a star is 13000 light years away, doesn't that mean we are seeing 13000-year-old light? If it does, then does that mean when we discover a planet with dimming star light, we are seeing a planet ...
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2answers
23k views

What is the exact time Earth takes to revolve around its axis? [closed]

I read that our day is not exactly 24 hours long. If it is not then why weather seasons come at the same time (Summer, Winter, Autumn Spring) ? how it is equalized ? Update: Sorry I could not make it ...
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2answers
319 views

How is distance in light-years converted to years back in time?

When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened. Would it be ...
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2answers
282 views

Why do we use the Planck length?

We are not able to quantize spacetime and the theory of loop quantum gravity has been proved wrong but we still use the Planck length in astrophysics. Why?
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1answer
324 views

Will I age slower in space or on other planets? [closed]

I came across few videos which says Astronauts in ISS will have 0.07 seconds extra life. So if life is possible on mars, than what is the time period of life for ...
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3answers
222 views

Knowing time any where and any when

My question is if I put you down somewhere in the Milky Way galaxy in any given period of time, is there a way for you to tell when and where you are based on stars or constellations? Or some known ...
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3answers
1k views

Why can't gravity repel things?

Gravity is the result of the curvature of space, so could the curvature actually send objects away from the source?
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1answer
273 views

What is length of the universe on lights perspective

According to Einsteins theory of special relativity, when something is travelling close to light speed, travel path is contracted. When the traveller is light itself, does it see the travel path ...
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2answers
283 views

Does spacetime return to being flat?

I wrote an experiment in HTML5 and Javascript to try to show what is happening to the curvature of spacetime as a body moves through a region. As time progresses, I'm using the ...
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1answer
212 views

Assuming proton decay is false, what's the ultimate fate of a neutron star or white dwarf?

A still unproven theory that protons can decay, and have a halflife of $10^{30}$ years or so, meaning eventually all matter will dissolve because their constituent protons and therefore neutrons will ...
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2answers
414 views

How could universe inflate itself out of the very dense and curved early spacetime? Could it happen in a black hole too?

Wasn't spacetime as much curved as a black hole directly after Big Bang, because mass was so densly packed? Wasn't everything like an event horizon and how could things expand across it? Could ...
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2answers
193 views

Why is space and time spoken of as one thing

I've never understood why it's spacetime and not space and time. In other words why aren't space and time spoken of as two different things. Can someone explain to me why this is
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1answer
139 views

When I read that a system is located x light years away, why is there no direction?

Well, I just read an article about a galaxy with two black holes, and it stated that the galaxy is 1 billion light-years away. Why is there no direction given? If the Big Bang happened, and things are ...
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1answer
119 views

Is it possible make artificial gravitational waves?

Is it possible to generate gravitational waves (creating low or high disturbance in space-time) from very heavy bodies spinning at very high speed artificially?
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3answers
361 views

Why is time considered a (fourth) dimension?

Since dimensions usually refer to space and we naturally acknowledge three of them, we also perceive time and we separate space from time ("space AND time"), why is it, that time has ended up in the ...
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1answer
187 views

In layman's terms, why do we put the "time" in space-time?

What does "time" mean in the term space-time? I am trying to understand why anything that travels through space, from a proton to massive galaxies, is always referred to as traveling in space-time, ...
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1answer
258 views

How could we tell if the Universe is infinite? [duplicate]

I've heard from a number of people that the Universe is infinite, and from my perspective, I can't see how this can actually be known, especially given that the Universe started out a finite size and ...
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2answers
625 views

What is gravity really?

What is gravity? I want to know more than it being simply the "mysterious force" that attracts things to earth. Is it a particle, a wave, or something else entirely?
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1answer
78 views

What exactly is space-time fabric?

I have heard about space-time fabric but I can't understand its definition. Is space-time fabric a physical thing or did Einstein imagine it to assist him with general relativity?
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1answer
110 views

Is it possible to overcome the problem of blind spot(s) of current gravitational wave detectors?

If gravitational wave pass through specific points (which are know as blind spots) current GW detectors aren't able to detect the passed waves so over the time will we be able to completely overcome ...
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1answer
401 views

How does an absolute horizon form before the apparent horizon?

If I understand it correctly, the apparent horizon is the boundary between where light directed outwards will move outwards, and light directed outwards will move inwards. Even if light is moving away ...
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2answers
562 views

Is time itself speeding up universally?

Time moves more slowly near a mass than in relatively empty space. For example, I get that an observer would see someone falling into a black hole to appear to move more slowly and get "stuck" on the ...
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1answer
164 views

Taking Advantage of Time Dilation

According to Einstein's theory of Special Relativity, one's speed in relation to a relatively stationary object would 'slow down' time on the moving object. With this in mind, would it be possible to ...
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1answer
453 views

Discontinuity in space-time

What I understood about it till now is that space-time fabric is kind of broken there. Please tell me whether I am correct. If it's true then does it mean that perception of time will stop there? I ...
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1answer
631 views

Total mass of light? [duplicate]

I know that light is considered as energy, and as such has a mass. So it is certainly taken into account in universes models and calculations. So I'm wondering: How much of the total mass of the ...
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1answer
295 views

Why does disorder (entropy) increase in the same direction of time as that in which the universe expands?

Why does disorder (entropy) increase in the same direction of time. as that in which the universe expands? Why can't entropy decrease in the same direction in which it increases ?
3
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1answer
55 views

Do astronomers, in principle, have more information about older phenomena than younger?

The further away we see, the older states of the world we observe. And the volume of the part of space which is observable, increases by the square of the distance to it. So there should basically be ...
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1answer
71 views

World line coordinate finiteness

If you trace two particles' world line backwards in time, according to current theory, both objects should converge at big bang. Would both objects arrive there simultaneously? Another way of asking ...
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0answers
87 views

The nature of cosmological inflation — unfolding dimensions?

While the paradigm of cosmological inflation is well established, the nature of the inflation is not known and is tackled by introduction of a hypothetical "inflaton" field. I was wondering if there ...
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3answers
189 views

What is the oldest thing?

I'm well aware of the celestial bodies considered as the oldest visible in our galaxy. My question might feel a bit odd: What is the oldest thing in the universe? I am puzzled with this question as ...
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2answers
245 views

What are the dimensions of LIGO Detector evacuated chambers?

The LIGO complex is very large, but I assume that there is a very small chamber that actually does the science since they are measuring very small sheers. How big around is the actual evacuated ...
2
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2answers
337 views

A camera and time dilation?

If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. However, what if we sent a probe with a camera to a black hole? When we watch the ...
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3answers
542 views

Is space a thing? [closed]

Based on my extent of knowledge relating to astrophysics, I once thought space is a thing, which can be twisted a long side with Time regarding masses of objects(According to relativity theory). But ...
2
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2answers
232 views

Beginning of space-time

I have read that the Big Bang created space-time, but how could this be possible? The Big Bang was itself a singularity, and a singularity is a point in space-time where the curvature becomes infinite....
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3answers
320 views

How does time work beyond the cosmic event horizon?

The faster you move through space, the slower you move through time - the calculations show that as you approach lightspeed, time comes to a standstill. How does time work beyond the cosmic event ...
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1answer
366 views

Why we can't see our Sun as it was a few years ago?

Our Sun is orbiting the center of the Milky Way galaxy. So many years ago, it was at a different location from where it is now. In addition, we are observing stars and exoplanets as they were many ...
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1answer
122 views

What exactly is the cosmic definition of ‘now’ is?

There is no cosmic definition of now because of special relativity, because of rate at which time flows for a particular object depends upon your point of view and your velocity. For a rocket ...
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1answer
99 views

Could the accelerating expansion of universe inidicate we are surrounded by "denser" space? [closed]

I'm quite novice about all this, only have read some vulgarization books and sites, but I wonder: could all the observable universe be falling outwards on some non-observable, more compact kind of ...
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2answers
385 views

Why doesn't this paradox disprove (some) multiverse quantum gravitational theories?

As I understand it, one theory of the multiverse is that there are an infinite number of universes separated by small distances in other (than our observable 3/4) dimensions and that gravity is weak ...
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2answers
170 views

Is time taken into account by astronomers when creating and using maps of the universe?

There's really two questions I'm asking. Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those ...