Questions tagged [space-time]

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

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26 views

Can expansion of space cause the motion of galaxies, does expansion of space do effect motion of our sun around center and earth around Sun?

I'm just wondering that expansion is anyway related to in effecting motion of a star under the galaxies ? Planets are currently revolving around sun in helix motion, if galaxies has motion as well ...
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Does time flow in a Minkowski spacetime?

In a spacetime where the stress-energy tensor is null (no energy, no matter, no entropy), I wonder whether any motion of the variable time in the phase-space is well defined. The arrow of time, meant ...
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If time is not absolute and depends on the gravitational field, then why we keep using our own (particular) time in cosmology?

Sorry if my question is not really clear, but indeed it is not clear in my mind neither. But maybe some of you can help. Time is not absolute and can be affected by the gravitational potential. Now ...
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Types of Multiverses [closed]

Can anyone recommend me books or other online resources on the concept of the Multiverse, it types, and about higher mathematical dimensions of space-time. I have been interested in such topics for a ...
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First Confirmed Visual Observation of Gravitational Lensing

Is it possible to identify the first direct observation of the gravitational lensing? What object was lensed, and where did the energy detected fall on the electromagnetic spectrum?
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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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104 views

Will the “fabric of space time” rip from expansion?

I'm quite familiar with the fabric of space time theory and as I've been quite lonely these past few weeks, I started thinking that since the universe is expanding and since the "fabric" is the ...
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Why are pseudo-Newtonian potentials used in studies of accretion processes around black holes?

In accretion processes around black holes, pseudo-Newtonian potentials are defined for the the black hole geometry. For examples, the potentials defined by Paczynski-Wiita and Artemova et al. for ...
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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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With the expansion of the universe is time also increasing?

With more space being created would there be more time in that new region formed? Is the over all universe increasing in time? This is my first question so go easy on me. PS. Would that also mean that ...
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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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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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Based off of the study that found the universe has a positive curvature, how big would the whole universe be?

This study found that the universe has a positive curvature https://www.nature.com/articles/s41550-019-0906-9. I didn't really want to buy it and see if it says how big the universe might be. I know ...
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Whats the time dilation difference between the earths reference and (near) the milky way galaxy central black hole? [duplicate]

How much difference in time is there between our time of reference and very near the black hole at the center of our galaxy. I was trying to get answer in terms of something like "1 year in here ...
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Neutron star size in different reference frames

What is the estimated size of neutron stars observed in their reference frame and in our reference frame? That is, how bent is space-time around neutron stars?
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How is time defined in astronomy?

I was amazed when my teacher told me that in space, time is define as a coordinate. It means we can define something with a four coordinate system with "negative time" $-t$ as easily as we can say $-...
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187 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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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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165 views

Do gravitationally bound (e.g. orbiting) objects really resist the expansion of space?

Thinking about the expansion of space, it is commonly explained that gravitationally bound objects (like galaxies and galaxy clusters) will not be affected by the expansion of space (dark energy). I ...
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265 views

Will intergalactic travel be impossible in roughly 15 billion years?

Even if we (or aliens somewhere in the universe living at that time) somehow invent something that can go just short of the speed of light, will intergalactic travel still be impossible in roughly 15 ...
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How can we see stars if they are hundred years of light far from the Earth?

So the right question is, is the light years counted from that second when you look up to the sky? If that so, how can we see the stars from the telescope (which I think it starts when you put your ...
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194 views

What is the time dilation less a magnetic field?

Does time dilation drop off like a gravity or does resemble a magnetic field model? Could a smaller body with a magnetic field have more time dilation then a larger body without and to what degree?
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342 views

Universe is expanding, why doesn't time expand with it?

Reading this response When the universe expands does it create new space, matter, or something else? I understand Universe is not expanding like if it is stretching its space, but it is actually ...
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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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238 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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55 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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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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131 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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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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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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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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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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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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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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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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213 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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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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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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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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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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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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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 ...
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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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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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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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629 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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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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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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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 ...