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Questions tagged [space-time]

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

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How is gravity a force if it is the result of space-time warping and bending?

If gravity is just the result of the bending of space-time, how does that make it a force? Isn’t it just an interaction between celestial bodies?
Prince Pugs's user avatar
0 votes
0 answers
19 views

How is it known that the stars move in the universe because spacetime is expanding and not that the stars expand through empty space? [duplicate]

Quoting one article, This expansion should not be thought of as stars flying away from each other in a static spacetime fabric. Instead, the stars are more or less static relative to a spacetime ...
Pablo's user avatar
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5 votes
3 answers
2k views

Is the gravitational constant really constant over our Universe?

For instance, if objects are travelling at relatively high speed around 'c', is G the same value for them as for us on earth? I believe a lot of matter is travelling fast away from other matter, so is ...
Bryan Major's user avatar
2 votes
0 answers
143 views

What happens at the edge of a finite and "bounded" universe?

So far, we know only about two types of universes: Infinite and finite universes (Unbounded edition). In an infinite universe, there is no edge. Because well, an infinite space doesn't have an edge. ...
Alastor's user avatar
  • 2,658
21 votes
2 answers
3k views

Does seeing a gravitationally lensed/magnified galaxy imply that they could also see us as well?

Does an observer in that galaxy see our galaxy magnified as well?
2080's user avatar
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7 votes
3 answers
2k views

How do we work out the light travel time on a cosmic scale?

I just read this article in the AUSTRALIAN SKY & TELESCOPE magazine, Nov/Dec 2022 Issue 140, on P16, KEEP YOUR DISTANCE: How far away are the objects we see in the universe? And on P23: "And ...
Curious Cat's user avatar
3 votes
4 answers
294 views

What makes space space?

Consider a situation where everything is removed from the Universe. All matter, all radiation, everything. Only a completely black void would remain. But what is it? What is this empty "space&...
juzzlin's user avatar
  • 165
0 votes
1 answer
151 views

What is everything wrong with this theory of dark matter?

So I had a hypothesis about why dark matter exists, but seeing as I've just barely begun studying astrophysics its most likely chock full of misconceptions and oversights. Here's a diagram of the ...
Aryaman Rtunjay's user avatar
-1 votes
1 answer
119 views

Could vacuum expansion arising from the Big Bang be a consequence of entanglement?

The model assumed here is that the vacuum is a coherent 4-d manifold, embedded in a background of quantum spacetime “foam”, or bulk. It is further assumed the bulk is itself disentangled, possessing ...
RalphW's user avatar
  • 33
0 votes
0 answers
59 views

Question about how it's possible for black holes to have gravity and a possible resolution [duplicate]

1. Assumptions 1.a: gravity propagates at c (maximum) 1.b: gravitational fields cause time dilation 1.c: escape velocity at the event horizon is c 1.d: gravity "warps" space-time, but in ...
P Varga's user avatar
  • 190
3 votes
2 answers
3k views

Why can't dark energy be considered a 5th fundamental force?

So I have recently been researching for multiple articles about fundamental forces, currently there are just 4 forces: Gravity Electromagnetism Strong nuclear force Weak nuclear force So far there ...
Alastor's user avatar
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0 votes
1 answer
118 views

If E.T. alien civilizations exist, won't those exoplanets be almost the age and rate of progress as ours? [closed]

This question is posed also as a mini theory, although I am really asking if someone knows how some parts of our universe would be far-more advanced if "everything" started at the same time (...
Dr. Deshando's user avatar
2 votes
1 answer
75 views

How would the symmetry of time dilation behave if a wormhole sent you near the rest observer?

The scenario I'm envisioning is this: A spaceship ("the ship") departs from a rest position ("Point A" or "the planet"), and travels at a relativistic speed towards Point ...
Arkathorn's user avatar
19 votes
2 answers
3k views

Could we (Earth, Humanity, Solar System) be falling into a black hole?

With the expansion of the universe, all objects far away from us appear to be moving away (ie: exhibit Redshift). With distance, this acceleration / redshift also seems to increase (~73,000 (m/s) / (...
G. Putnam's user avatar
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0 votes
0 answers
28 views

Can the cosmological constant be coupled to redshift of radiation

Can space-time be more embedded with the things inside it than we actually think?Can the redshift of radiation be a property of spacetime and that dark energy exists only to conserve the overall ...
appliedSciences's user avatar
0 votes
1 answer
207 views

Space travel relative to solar system's movement through space

Assuming our entire system (stars, planets, etc) is moving through space at around 180,000 mph. Why can't we leave in a direction opposite our system's movement to achieve deepspace flight? Part two ...
James Long's user avatar
1 vote
0 answers
53 views

Does the (relative) distance of the photon sphere from the center of a black hole vary according its mass?

I know that the photon circle or photon sphere is located at around 1.5 times the radius of the Schwarzschild event horizon, but wouldn't it be comparatively further out for smaller black holes? After ...
Kurt Hikes's user avatar
  • 5,097
4 votes
0 answers
68 views

What does it exactly mean for spacetime to have no global symmetries?

Are there spacetimes or metrics with no global symmetries? Spacetimes/metrics with no global Poincaré, Lorentz, diffeomorphism, CPT, translational and gauge invariances? And if there are, what does it ...
vengaq's user avatar
  • 937
1 vote
0 answers
68 views

Non-homogeneous and anisotropic metric and laws of physics...?

In this popular science article, they say that if our universe resulted to be non-uniform (that is highly anisotropic and inhomogeneous) then the fundamental laws of physics could change from place to ...
vengaq's user avatar
  • 937
1 vote
0 answers
27 views

Spacetimes where symmetries vary from place to place?

Are there spacetimes or metrics where symmetries (like Poincaré, Lorentz, diffeomorphism, translational... invariances) are only local and the symmetries of one local neighbourhood are not, a priori, ...
vengaq's user avatar
  • 937
2 votes
1 answer
80 views

Are there non-smooth metrics for spacetime (that don't involve singularities)?

I found this statement in a discussion about the application of local Lorentz symmetry in spacetime metrics: Lorentz invariance holds locally in GR, but you're right that it no longer applies ...
vengaq's user avatar
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1 vote
1 answer
77 views

Could inhomogeneities or topological defects break the fundamental symmetries of the Universe?

I have heard that some types of inhomogeneities and topological defects in cosmology have been proposed to be able to break fundamental symmetries of nature such as the Poincaré, Lorentz, ...
vengaq's user avatar
  • 937
1 vote
1 answer
292 views

Does the expansion of space stretch the space-time fabric?

This question appeared to me when I was thinking about General Relativity. During the expansion of space, the space in which particles reside is expanded. Now, general relativity states gravity is the ...
Naveen V's user avatar
  • 161
6 votes
2 answers
284 views

Light or neutrinos graze or pass through the Sun and arrive at Earth - need an expression for Sun's gravitational effect on observation direction/time

Skyfield's Github has discussion Jupiter hiccup #815 which then links back to to Non-physical gravitational deflection corrections for Solar System bodies #734. The script and plot from #815 are shown ...
uhoh's user avatar
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20 votes
5 answers
6k views

Why is time referred to as "The" capital T 4th dimension?

Often you hear people say "time is The 4th dimension". What confuses me is that people talk about "The 4th" dimension as if it's a specific thing and I don't understand why. What I ...
Michael Seltenreich's user avatar
2 votes
1 answer
404 views

Would an observer standing at the edge of the "observable universe" perceive the expansion of space-time?

I got this bizarre idea in my mind, after reading SCP-3321 There, as a person gets teleported through a wormhole, ends up at the edge of the Observable Universe, 46 billion light-years away from Earth....
Alastor's user avatar
  • 2,658
0 votes
1 answer
117 views

Time and space travel as applied to expanding space and the ratio of/between time and distance

If a place is 500 light years away, then I set out to this place, then is it true to say that, the place which I set out from, will be 750 light years away from my destination, once I have reached it? ...
Lux Magi's user avatar
1 vote
2 answers
2k views

If Looking Into Space is Like Looking Back in Time, Why is it the Same in Every Direction?

After seeing the James Webb space picture, in which a tiny sliver of the sky the size of a piece of rice from our perspective here on Earth was examined and revealed contain, as expected, an abundance ...
Jack Casali's user avatar
1 vote
1 answer
72 views

How would a balloon structure of a universe look if we collected all mass together in a small region?

Imagine a universe with an inflating balloon structure of spacetime. Matter is distributed uniformly. Now somehow we manage to collect all matter together within a small volume. What would happen to ...
Felicia's user avatar
1 vote
3 answers
320 views

Does dark energy make galaxies expand over long periods of time?

Does dark energy expand galaxies slightly over time? I would think this could be verified easily (observe if galaxies far away / further in the past smaller and denser), and might make a good ...
Jonathan's user avatar
  • 4,385
-6 votes
1 answer
133 views

In relativity why does matter bend spacetime in a downward direction [closed]

A major flaw , I think it is in relativity.
Kapish Lakhotia's user avatar
0 votes
1 answer
61 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 ...
Alex's user avatar
  • 701
20 votes
5 answers
7k 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 ...
PunchyRascal's user avatar
1 vote
1 answer
108 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?
Kurt Hikes's user avatar
  • 5,097
3 votes
1 answer
514 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?
Aditya Radadiya's user avatar
1 vote
0 answers
111 views

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? ...
Maharshi's user avatar
  • 111
18 votes
6 answers
7k views

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, ...
Psychonaut's user avatar
8 votes
1 answer
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 ...
stevec's user avatar
  • 181
3 votes
1 answer
637 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 ...
user random numbers's user avatar
3 votes
6 answers
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 ...
johnny's user avatar
  • 185
5 votes
2 answers
1k 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 ...
Sazzad Hissain Khan's user avatar
40 votes
3 answers
12k views

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, ...
Sazzad Hissain Khan's user avatar
1 vote
3 answers
2k 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 ...
Pouya Samie's user avatar
0 votes
0 answers
58 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 ...
NikoEraser's user avatar
1 vote
1 answer
285 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 ...
Amartya's user avatar
  • 153
1 vote
1 answer
46 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 ...
MIKEY SINGH's user avatar
0 votes
0 answers
79 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 ...
user avatar
2 votes
0 answers
83 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 ...
user avatar
2 votes
1 answer
86 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 ...
user34161's user avatar
0 votes
1 answer
134 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?
BigNutz's user avatar
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