As a consequence of the Lorentz transformations, time and space transform into each other when changing reference frame. This calls for a unified description: Minkowski spacetime.

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1answer
60 views

“Spacetime tells matter how to move; matter tells spacetime how to curve” and acceleration in flat space-time? [closed]

John Wheeler stated "Spacetime tells matter how to move; matter tells spacetime how to curve." Does this contradict with the assumption that mass can be accelerated in flat space-time (see i.e. this ...
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2answers
140 views

Einstein wrote $x^4=ict$, where $c$ is the speed of light. Does this mean the fourth dimension is moving? [closed]

Saw this on a forum: Einstein wrote$x^4=ict$, where $c$ is the speed of light. Does this mean the fourth dimension is moving? We can write $x^4=ict$ as $dx^4/dt =ic$. The fourth dimensions is thus ...
3
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2answers
88 views

Gravity and spacetime bending [duplicate]

Something that puzzles me if gravity is just bending of space time near a mass then what is gravitational force? If say two massive bodies were perfectly at rest relative to each other they would ...
-1
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1answer
37 views

Do we exist in warped space and time?

Does the Suns altering of space and time (as evidenced at an eclipse) extend to the Earth such that we exist in warped space and time or are we outside those effects.
0
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1answer
36 views

Is turning space into time and time into space possible from an observer's perspective?

If the distinction between space and time depends on the reference frame, what reference frame should we use to perceive time as space and space as time?
4
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3answers
578 views

Could a finite amount of space in the universe exist without time? [closed]

Is it possible that a finite amount of space in the universe exists without time? Namely, that it is possible for us to find an element of space that has no time (everything happened at one point and ...
0
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1answer
83 views

Has there been any analysis on LIGO data looking for a 24 hour frequency?

The reason I ask this is because it seems like it would be a simple analysis to run with all the data we have and it would tell us if the land-based LIGO detectors pick up anything depending on our ...
1
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0answers
37 views

What is the space-time medium? [closed]

What is the space-time medium? According to this answer: "... fields are a fundamental part of the universe." Then why do we describe a gravity as being depressions in space-time? And why don't we ...
1
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1answer
35 views

Function to model deformed spacetime in 2D visualization of an Alcubierre drive

In the Wikipedia article on Alcubierre drive there is a top image. It is 2D visualization of an Alcubierre drive, showing the opposing regions of expanding and contracting space-time that displace the ...
0
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0answers
18 views

Is the fabric of space time a real thing? [duplicate]

With ny limited intelligence I think Einstein said that the gravity is caused by a curvature in spacetime.But unless there is an actual feelable fabric(or someting similar) how is a curvature caused ...
2
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0answers
52 views

Closed timelike curves in the Kerr metric

I just read in Landau-Lifshitz that the Kerr metric admits closed timelike curves in the region $r \in (0, r_{hor})$ where $r_{hor}$ is the event-horizon ( I am talking about the case $|M|>|a|$ ...
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2answers
36 views

Curvy space in and around massive objects [closed]

If space curves around massive objects, what happens to the space within the massive objects?
2
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0answers
61 views

Should we consider space and time as separate entity?

In general relativity, we think of space and time in spacetime framework. As some people say, metric tensor sign difference, along with our inability to go backward in time suggests that space and ...
0
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0answers
35 views

Time. Is it really a dimension? [duplicate]

I have trouble accepting that time is a dimension, in the same way that space has three dimensions. Wherever there is space and matter, it has spatial properties. You can move back and forwards in ...
3
votes
2answers
145 views

Is curvature space-time has impact on the object geometry

When we have e.g. metallic cube of dimensions 1x1x1m and we put it on the space without gravitational force the cube has equal 1x1x1m and we can use Euclidean geometry. But when this cube move on ...
1
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2answers
95 views

A twin-like paradox, with no acceleration and no 3rd reference point. What would happen?

The following is a variation on the twin paradox, with no acceleration and no 3rd reference point (i.e. described purely in terms of relative motion). Imagine two observers initially located right ...
0
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1answer
161 views

Does Inertial time dilation demonstrate that Time is not a dimension? [duplicate]

If time is a dimension and 'now' simply an expression of your position with respect to that dimension, the progress of any object along that dimension should remain in step with all other objects. By ...
1
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0answers
29 views

Why doesn't electricity and magnetism distort space as well? [duplicate]

I think Kaluza/Klein was partly worked on to find additional dimensions to account for electric and magnetic fields. I am confused why the gravity field gets the privileged spot of distorting ...
0
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1answer
71 views

What happens to spacetime in a universe with no clocks?

For example, in the far future when all matter has been absorbed into BHs which have evaporated leaving only photons.
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2answers
246 views

What would have been the story of the Universe if there was no mechanism to produce massive fundamental baryonic particles? [duplicate]

Thanks for those of you who took their time answering my problem but it seems that there is a misunderstanding between us. Most answers are based on the assumption of Electroweak symmetry breaking ...
6
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2answers
2k views

Does the existence of “gravitational waves” (assuming they exist) imply that time exists as a 4th dimension in the universe? [closed]

I'm new to thinking about special and general relativity and I have no formal training as a physicist. However, I've been doing a bit of thinking about spacetime recently. I was wondering if ...
3
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1answer
47 views

Frame dragging resulting in an orbital plane?

In astrophysics today we talked about spinning black holes, ring singularities, and frame dragging. Is this also (to some degree) the cause of the milky way being as flat as it is? Does the spin of ...
0
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1answer
44 views

3 points in space, relative motion, and the speed of light

I'm new to thinking about relativity, as well as phenomena related to the speed of light, time dilation, length contraction, simultaneity, etc. I am pondering a paradox. Assumptions: Motion is ...
0
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3answers
139 views

Is time unidirectional because of 4th spatial dimension? [closed]

We heard about an expanding universe. Consider an expanding sphere. Consider the surface of the sphere as our 3 dimensional universe. Can time dimension be the radius $R$ of this sphere? And because ...
0
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1answer
43 views

Does volume of an object affect space-tme curvature? [closed]

If I have 2 bodies of same mass, let 100 tonnes, Both have different volume, let one of $1m^3$ and other of $10,00,000m^3$. Which would have more gravity. Consider here that affect of gravity by ...
1
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1answer
35 views

Lorentz Invariants and Time dilation/Distance contraction?

If distances contract in direction of motion and time dilates at high speeds, why are the rest mass $m_0$ and proper time $t_0$ called "invariant" under Lorentz transformations. Since depending on ...
2
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0answers
41 views

Could a 3+1 space be embedded in a 4+1 space and retain its 3+1 characteristics? [closed]

I'm confused because I can conceptualize this embedding scenario in two seemingly incompatible ways. Which of the following scenarios are possible?: 1) 4+1 space automatically enforces 4 dimensions ...
2
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2answers
41 views

How object's movement is separated from the space-time movement?

In Issues related to expansion of the universe while space-time itself is moving how it is possible to calculate the speed of an moving object? In other words how object's movement is separated from ...
1
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3answers
83 views

How/why does gravity affect spacetime? [duplicate]

I've always heard that gravity warpes spacetime, but I've never understood why and/or how. I'm only 12 so please keep it simple if possible.
1
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1answer
42 views

Could the rest mass be somehow considered as a very exotic kind of kinetic energy?

In its rest frame a free system of invariant mass $m$ has energy $E=mc^{2}$. That frame is moving in spacetime with a four-velocity whose magnitude is $c$. Inside my brain something asks: Would ...
12
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3answers
1k views

How does gravity truly work? [duplicate]

I Am only 12 years old and I'm constantly wondering and trying understand how gravity really works. On YouTube everyone always talks about objects wrapping space time around themselves and uses the ...
-1
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1answer
66 views

Wouldn't it take an infinite amount of time to create an infinite universe? [duplicate]

I have heard many people say that the universe is possible infinite. But, if it takes time and energy to create bodies such as planets and stars and the universe has only existed for 13.7 billion ...
3
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0answers
26 views

Parity and Time reversal when the number of space or time dimensions is even

There's a side remark in the middle of section 2.6 of Weinberg I that I find a bit unclear. Suppose that $L(p)$ is a boost that carries the four momentum $k^\mu=(0,0,0,M)$ to $p^\mu$, and that ${\bf ...
0
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1answer
59 views

Does mass compress space-time?

My understanding of relativity explains that the presence of mass warps space-time so that light travelling through the warp follows at straight line but the warp itself is curved and therefore the ...
1
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1answer
63 views

Questions about how the curvature of universe is described with a single number

I often read of physics talking about "the" curvature of the universe, giving it some letter $K$, and claiming that we have seen that $K = 0$ within such and such certainty. I have three questions: ...
1
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0answers
80 views

Absolute direction of time [closed]

As Universe is expanding into emptyness, we think that flow of time is forward. This means that expansion is directed forward in time. Even though we don't know for sure whether this expansion will be ...
0
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2answers
64 views

Don't rulers expand at the same rate as the universe they measure? [duplicate]

If you placed a giant ruler between the sun and our nearest star for example, wouldn't the divisions on the ruler expand at the same rate as the universe - therefore maintaining a constant distance? ...
2
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2answers
80 views

Can gravity prevent quantum superposition of positions for a massive object?

Theoretically, nothing prevents a really massive object to be in a superposition of two spatial locations, even far away one from the other. Then I guess spacetime would also show the superposition of ...
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votes
1answer
45 views

Since Alcubierre drive moves a flat region of space, does it mean that space acts lika a liquid? [closed]

The Alcubierre drive would move a patch of flat space through space and, leaving exotic matter aside, is mathematically correct. Does that means that space-time is not a "solid" lattice i.e. not ...
2
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2answers
56 views

Could it be possible to bend space in more than one “way”?

Ever since the announcement of the discovery of gravitational waves, I have found myself pondering related notions of space. Recently, I was thinking about an analogy I've heard to explain how mass ...
0
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1answer
61 views

Black hole's singularity: Does it has to be multi-dimensional?

We assume that there is an infinite density at the center of a black hole. But we also know that if it was really infinite, it would apply an infinite gravitational force to masses even if they were ...
0
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3answers
218 views

Two “devil's advocate” questions related to LIGO measurement results interpretation

"If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things." Rene Descartes Laymen like me typically refers to Wikipedia ...
0
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3answers
94 views

How is Space-Time produced? [closed]

The parable of the ant walking on the surface of a balloon tells us that as the balloon expands, more of surface is created, hence more place for the ant to walk. Space-Time is also in the same ...
0
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2answers
84 views

How do you know what kind of space(time) you have when solving the Einstein Field Equations?

I'm experimenting with the EFE, and I ''invented'' a metric; a diagonal non-zero metric, and I discovered that the Riemann tensors are equal to zero which implies the Einstein tensor $G_{mn}$ equals ...
0
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1answer
55 views

What dictates the rate in which time passes? [closed]

I understand that special relativity tells us that our perception of the passage of time can change depending on reference frames. But why does time pass the rate at which it does in my reference ...
1
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0answers
93 views

What is the justification for continuing to model space-time as a manifold in string theory?

Background The question I have arises from taking seriously the idea that, in a physical theory, one should first define all physical quantities via (thought) experiment. Justification and ...
3
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1answer
52 views

Is the cosmological horizon expanding faster than space itself?

I read that the rate of expansion of the universe is still a mystery. But if it's actually decelerating, wouldn't it mean that our cosmological horizon is expanding faster than space, and that one day ...
1
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0answers
22 views

Time in the early universe [duplicate]

When it is said, for example, that grand unification took place "Between 10−43 second and 10−36 second after the Big Bang", how are these figures of time derived? Moreover, do these figures have any ...
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votes
1answer
94 views

Time slows down as you approach the speed of light, travelers observe speeds faster than light travel? [closed]

If I was on a spaceship traveling almost at the speed of light, my time would slow down relative to the time for a stationary external observer. My question is, since we measure distances between ...
0
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0answers
55 views

Scale factor of the universe

Do we impose that the scale factor $a(t)$ of the Universe is a continuous function? Or there is a physical meaning? Usually in physics we define functions to be continuous, such as the velocity of a ...