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Questions tagged [space-time]

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

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Why do heavy objects bend space-time downwards? [on hold]

Einstein's general theory of relativity is famously demonstrated using stretched sheet and marbles. We all know the demonstration. But its GRAVITY itself which makes the stretching of the sheet ...
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3answers
235 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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How does a spinning black hole affect space-time compared to a non-spinning black hole?

I often see questions on this site that only apply to non-spinning black holes and often wonder how the answer would be different for a spinning black hole. As the title says, what are the major ...
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1answer
95 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
53 views

What would happen if space-time began to contract? [closed]

Assume that the expansion of the universe stops and it starts to contract again. What would happen? Would only distances between objects get smaller, or are there other effects we can expect?
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1answer
85 views

Looking at the Expanding Universe through the lens of relativity [closed]

The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light. I am assuming it has been thought about or maybe ...
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1answer
87 views

Why does gravity make time go slower and warp light?

I know that objects with lots of gravity are capable of warping light or slowing time (an example being a black hole). I also know this is because of the theory of relativity, but I need someone to ...
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3answers
2k views

Can we track matter through time by looking at different depths in space?

If we look back far enough we can see all the origins of the universe, so is it possible, even if not feasible, that we could trace the history of some matter as it moves through space-time? I want to ...
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63 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
152 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 ...
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2answers
101 views

What is the difference between the way light travels in a gravitational field and the way it travels through an expanding universe?

A photon is travelling through space. As it travels, the space through which it travels is expanding Does this describe A - a photon travelling from a distant galaxy to earth B - a photon travelling ...
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2answers
118 views

Does the Milky Way's movement through space have spacetime implications?

The way I usually see spacetime explained, it says that if you just sit still, you are moving at 0kph and so you are moving at maximum speed through time (ie. time for you is flowing at maximum speed)....
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1answer
71 views

What is the exact meaning of vicinity of Black hole or a disk? the same as inside?

What is the exact meaning of vicinity of Blackhole or a disk? Is this the same as inside the horizon for black holes? If so, why people don't say inside of BH, simply. What is the difference? I use ...
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1answer
63 views

How to convert factors of time dilation into something relatable? [duplicate]

On this post, Time according to the gravity of Sagittarius A? They found the factor of time on the varying distances from the SMBH, I am curious on how to turn those factors into relatable terms ...
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2answers
162 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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0answers
38 views

How to compare the observation with the theoretically predicted result?

On the Wikipedia Article on “Geodesics in general relativity”, it says the following: “Thus, for example, the path of a planet orbiting a star is the projection of a geodesic of the curved 4-D ...
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1answer
67 views

How can the universe be expanding? [duplicate]

I assume expansion implies an increase in the volume of the universe. But if the volume of the universe is increasing, does that not imply the area it is expanding into's volume is being reduced?
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2answers
160 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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2answers
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Since gravity is like an indent on a piece of paper (the space/time matrix) to a marble, can the black hole eventually suck in the matrix?

Can a black hole suck in time? People claim that if you were to put a bowling ball on a trampoline and rolled much smaller balls through the deppression, some would stay in "orbit", some would roll ...
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2answers
76 views

Is there a limit to how fast spacetime can bend/warp around an accelerating object?

If in the future a spaceship can accelerate to nearly the speed of light, will it encounter any kind of resistance/drag from the spacetime in front of it not being able to bend/warp fast enough around ...
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1answer
75 views

Does time dilation increase within overlapping gravitational fields?

If a spaceship was to travel to the barycenter of a binary star (the stars having identical size and mass) and come to a stop there, would the people on board this spaceship find that time is moving ...
2
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1answer
84 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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2answers
168 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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1answer
83 views

Space curvature and its rotation

As I learn, the gravity is caused by the spacetime curvature. Is there any gravitational/magnetic field that really exists around the Earth, or any other planets? Since the planets/stars rotate, does ...
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1answer
573 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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2answers
73 views

Dark Matter Curvature

Does Dark Matter affect Space Time Curvature? If so, then what is the formula to calculate space time curvature due to dark matter?
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1answer
745 views

What is the actual black hole merger speed?

I have seen models of 2 black hole mergers. https://www.theverge.com/2017/11/16/16665132/gravitational-waves-ligo-virgo-black-holes-merger-multi-messenger-astronomy When we see a space ship appear ...
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2answers
280 views

What is the fastest a galaxy or other body has been measured to (or can) travel?

Our solar system travels at an average speed of 515,000 mph and our galaxy at 1.3 million mph through space. What is the fastest moving body in space recorded and the fastest can a black hole or ...
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2answers
109 views

Are we really seeing the asteroids from the past?

Is it actually relevant to study objects that are light years far? Because in theories we are actually seeing the past as the light takes years to reach us. Lets say we are studying a asteroid that ...
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1answer
137 views

How well is Earth’s motion through the universe quantified?

If I had a time travel machine that could drop me into any point in space and time, could I accurately predict earth’s “position”? I know position is an improper term. Would it be possible to know ...
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3answers
211 views

Is the shape of observable universe and shape of space same?

I have read that Euclidean space is considered as flat space and Minkowski space is flat space-time. So when we say our observable universe is flat are we saying that the space is flat or space-time ...
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1answer
314 views

How does space time differ between galaxies? [duplicate]

Does the gravity wells differ enough between galaxies to have different speeds in space time? How much slower in space time would the biggest galaxy have compared to the Milky Way?
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2answers
257 views

How does space time differ within a galaxy?

Not the same question but is similar to other marked duplicate. How much time dilation does the center of a galaxy can exist and sustain human life from our point of view? What would a day equal to ...
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Gravitational eddies across the galaxy?

I read about natural gravitational eddies that travel in a wave that black holes have. They also have a strong magnetic field. Does those eddies follow magnetic field lines of the rotating black hole? ...
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1answer
74 views

Which quantum reality will be seen in a future Earth [closed]

If we orbit near a black hole to travel to future and come back to Earth, which of the quantum realities will be observed in the future Earth? My question is regarding many worlds interpretation of ...
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1answer
85 views

Which quantum reality will be seen in a far away galaxy [closed]

I recently watched Brian Greene documentaries on parallel universes and am trying to wrap my brain around multiple quantum universes that form at every event and Einstein's relativity that in space-...
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1answer
134 views

do rockets follow a straight path but is looks curved because of space time?

Does the path of a rocket or anything going straight up look curved because the mass of the earth is curving space-time? If we assume the earth, the rocket and all the celestial bodies whose ...
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2answers
699 views

Is spacetime hyperbolic?

I have always seen answers to this point to measurements of how "flat" local geometry is, but my problem is, thats space not spacetime. I would say its safe to say that the geometry of space in our ...
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1answer
65 views

Is it correct to assume that the relationship between an objects mass and size, is what decides if it’s a black hole or not?

I’m asking this question in reference to a scenario I saw posted a couple of days ago, where it’s stated that if you would shrink earth to the size of a cherry, it would become a black hole. Is it ...
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1answer
76 views

Time travel in past and future [closed]

Why it is not even theoretically possible to travel in past but possible to travel in future ?
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1answer
72 views

How entropy increases over time [closed]

According to 2nd law of thermodynamic, in an isolated system entropy increases over tume. In an open system entropy might seems decreases but combined result of all related events results in overall ...
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2answers
154 views

Canvas and bowling ball

I'm having trouble understanding the basic model for how matter bends space. The classic illustration is the canvas and the ball but that model needs a reference frame where one can define a downward ...
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2answers
136 views

What defines stationary vs spinning in space?

To produce artificial gravity on a space station, we simply spin it around some central point, and the acceleration makes objects "fall" outwards. If our space station is so far in deep space that it ...
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1answer
69 views

Maximum disturbance to space time of gravitational waves, and will this affect humans? [duplicate]

Do we have a theory that can tell us how much change gravitational waves can make to space time. If it is infinite then I think any time we can see biggest change in space time and how much could it ...
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2answers
260 views

Can we peek into a black hole with magnetic waves? [closed]

Aside from the fact that nothing we know of, excluding pure energy can escape from black holes. They affect both space and time in a manner that nothing else can quite compare to, and usually have ...
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3answers
193 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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1answer
273 views

Are wormholes even possible?

While this question could fall under Space Exploration or Physics (I don't have the "best" reputation on THAT forum), I feel that it is very much related to how the universe itself functions, ...
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0answers
60 views

Does a 4-manifold universe imply zero net energy?

If our universe is a 4-manifold (i.e. with every point in space-time already existing) does this imply that there is zero net energy (as net energy would do work and so change the universe)? If so, ...
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1answer
487 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
96 views

If the density of nebular distribution increases symmetrically in all directions, how does space curvature explain it?

Edwin Hubble, in The Observational Approach to Cosmology, wrote Thus the density of the nebular distribution increases outwards, symmetrically in all directions, leaving the observer in a unique ...