Questions tagged [space-time]

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

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3
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2answers
405 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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1answer
49 views

Does the combination of concepts of "cosmic sensorship" and "Gregory-Laflamme instability" correlate with the "string theory"?

Does the combination of concepts of "cosmic sensorship" and "Gregory-Laflamme instability" correlate with the "string theory" since it appears that both require ...
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What effect does time dilation have on bodies orbiting close to Black Holes?

As far as my (somewhat basic) knowledge of astrophysics goes in general the closer to a star your orbit gets smaller (because you travel less distance) and faster (because you're deeper in the gravity ...
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How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?

How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us? The question might look a bit odd but I am really stuck on my head. We know, ...
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1answer
193 views

Theoretically could the expansion of the universe affect acceleration due to gravity?

I was wondering if theoretically the universe expanding affects speed or acceleration due to gravity, compared to if space weren't accelerating. The way I have it in my head, something is falling ...
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3answers
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Would time go by infinitely fast when crossing the event horizon of a black hole?

If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the ...
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5answers
6k views

Is it suspicious that gravitational waves propagate at the speed of light?

Thinking about gravitational waves and the fact that they propagate at the speed of light, I was wondering if it isn't suspicious - the speed of light I mean. Does it perhaps point to something ...
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1answer
41 views

Why is the FLRW universe (general relativity solution(s)) sometimes called the 'FRW universe'?

Why is the letter L for Georges LeMaîtres often, or even usually, left out? Does he, or does he not, deserve some credit for this cosmological solution to Einstein's general relativity?
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777 views

Confused about rubber sheet analogy!

How to resolve confusions on the rubber sheet analogy of the spacetime curvatures? I am a newbie to spacetime curvature. I have watched several youtube videos on Einsteins GR and spacetime curvature ...
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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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0answers
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How do we know that spacetime is fabric? [closed]

I have started learning about astronomy as it amazes and inspires me. I have a question. What led us to believe that spacetime is fabric? What is the evidence shows this, and is it considered proven? ...
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1answer
261 views

A universal reference point [duplicate]

I would like to use a system of co-ordinates (x,y,z,t) based on a specific well known point. My original choice (the center of the universe in the big bang theory, Bigbang0), was wrong as the universe ...
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6answers
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If the Sun disappeared, could some planets form a new orbital system?

If the sun were to suddenly disappear, the planets would continue to travel tangentially to their former orbits. (This I know from this answer to a somewhat related question here.) In such a scenario, ...
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3answers
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Life planets orbiting black-holes. Can/Do they really exist?

So, I watched Interstellar and if you watched it too you know that there's a planet orbiting a black-hole, they call it Miller's Planet. According to the movie, every hour on Miller's Planet is ...
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5answers
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Why is the observable Universe larger than its age would suggest?

The age of the Universe is estimated at 13.8 billion years, and current theory states nothing can exceed the speed of light, which can lead to the incorrect conclusion that the universe can't have a ...
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0answers
52 views

How would you define "space" in GR (General Relativity) and in QFT (Quantum Field Theory)?

Is there a univocal definition of space that can be accepted in GR and in QFT? In GR space is actually "Spacetime", a 4-dimensional entity that includes time. In this case it's impossible to ...
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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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1answer
1k views

What are the stages in the life of a universe?

Geological periods describe varying phases in the last few hundred million years on earth. Are there any names for the periods on a timescale 1-2 orders of magnitude greater, that is, for the stages ...
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2answers
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Space time and aging

Would a more significant curvature of spacetime relative to earth (i.e. time on jupiter) effect the aging process? Basically would you age at a slower rate? Or age faster on the moon?
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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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1answer
213 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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8answers
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Does matter accumulate just outside the event horizon of a black hole?

My understanding is that time slows and approaches stopping when approaching the event horizon of a black hole. I have seen this explained several places, including a brief explanation in the last ...
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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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2answers
338 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
234 views

If the Sun disappears right now, when the absence of its gravity affects on Earth? [duplicate]

Imagine if the Sun disappears right now. When the Earth will be affected by its absence? Does it affect immediately, or it takes almost 8 minutes? (The time that light travels from the Sun to the ...
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1answer
574 views

In what ways does the mass and energy of the milky way curve space time?

Space is curved by mass (or more precisely by mass and momentum as described by the stress-energy tensor). The milky way system has a lot of mass and a lot of energy. In what ways is space-time curved ...
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1answer
118 views

Distance between two events

I would like to start from the very basic such as Pythagoras Theorem. If I want to calculate distance between two points in a right-angled Triangle We use $c^{2}= a^{2}+b^{2}$; Using this We are quite ...
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1answer
30 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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0answers
66 views

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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0answers
72 views

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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1answer
146 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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1answer
86 views

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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2answers
4k views

How long would it take to reach the edge of the reachable universe?

How long would it take to reach the current edge of the reachable portion of the universe, with the following bounds in mind: We figure out a way build a space ship to provide a constant 1 G ...
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1answer
72 views

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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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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2answers
121 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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3answers
27k views

When we see the Sun, do we actually see its past?

The Sun's rays hit our eyes around 8 minutes after they are emitted from the Sun. Does this mean that the Sun that we see is always the Sun as it was some 8 minutes before? I strongly think this must ...
3
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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
264 views

How would Special relativity explain past-present-future if thinking about 13-billion-light-years distanced objects

Halo. I'm interested in how would Special relativity comment on this: Suppose there are 2 objects, A and B. They are 13 billion light years away from each other. When the light from the B object ...
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0answers
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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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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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1answer
264 views

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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0answers
71 views

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 ...
3
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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
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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4answers
4k views

What is a singularity? What is at the center of a black hole? Specifically regarding space-time

So because I can only really think of space-time in 2-dimensions like a sheet of something, my assumptions might be wrong to begin with. I was watching a YouTube video on black-holes and there was a ...
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5answers
23k views

By putting a mirror in space, would we be able to see into the past?

I only ask this because of how fast light travels. The question remains in the title. Why, or why not, would this work?
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3answers
2k views

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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2answers
136 views

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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1answer
2k views

Time according to the gravity of Sagittarius A*?

This may be a really dumb question (I'm more of a Biologist than an Astronomer) so I apologize in advance for my little knowledge pertaining to Astronomy, but, if I'm not mistaken, time is effected by ...