# Tag Info

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We need to first ask ourselves what is Space? What is Time? Then we can begin to answer your question after we define what these two are and the relationship between them. According to Geometrical Mathematics and based on Numerical Vector Space is nothing more then an empty construct and has no Dimensions until you give it a coordinate. We can define space ...

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There are two parts to your question. First, why can we see things "46 billion light years away" if the Universe is only about 13.8 billion years old? Because the Universe is expanding. How far does a photon travel in 13.8 billion years in an expanding Universe? It depends on the rate of expansion. I'll give a simplified example to illustrate the point: ...

2

When they say the universe was the size of a baseball about a billion billion billion billionth of a second after the big bang, does that means the observable universe was the size of a baseball, or does it mean the entire universe? In the past, the answer would have been the entire universe. Big bang cosmology is all about the expanding universe starting ...

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Because near matter spacetime isn't expanding, and if it isn't expanding it can't be stretching the matter. The expansion of spacetime is a prediction of general relativity for the special case of a matter distribution that is homogenous and isotropic. If we feed in this condition we find that the geometry of spacetime is described by an equation called the ...

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General relativity deals with equivalence classes of maps. If you take one map of space-time, put it through a continuously differential equation, and alter the metric accordingly, you get an equivalent map. You can't talk about one or the other being right. They're equivalent. Either they're both right or they're both wrong. To be fair, that's just a ...

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I'm going to first address some misconceptions you seem to have and then I will get to answering your question. Now, as stated in the comments, @Pulsar did a very thorough job of answering this question in another post. But I read through that answer and it's a bit technical. I already knew the stuff, so it made sense to me, but I can see how someone ...

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In my Physics Class we had to look into possible areas where Dark Matter could be "hiding". Where is all the dark matter? Actually, I think it's hiding in plain sight. If you've read up on relativity I think you can work it out. See Einstein's Leyden Address where he described a gravitational field as space which was "neither homogeneous nor isotropic", and ...

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There are two main misconceptions about dark matter. One is that dark matter is a clump of stuff traveling with the matter. The other is that matter does not interact with dark matter. Dark matter fills 'empty' space. 'Empty' space has mass. Spacetime has mass. Dark matter is displaced by matter. The Milky Way moves through and curves spacetime. The ...

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There are several reasons to believe that dark matter is a particle. The most widely accepted alternative explanations for the different phenomena that led us to conjecture dark matter in the first place, can collectively be labeled "we don't understand gravity well enough". But no matter what, the effects of dark matter are sort of "localized". The ...

1

There are two ways I can answer this question. I'm pretty sure one of the ways is, while technically correct, mostly worthless to you because it ignore the question you're trying to ask and focuses on the question you did ask. So let's start with that one. The redshift used by Hubble comes from expansion only and from gravity only. In general relativity, ...

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From expansion of the universe, the expansion of the universe is a repulsive force. Why it is a force? Because just like gravity, it is from spacetime, eventually it pushes atoms apart

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The reason it's thought of as expansion of space rather than just things moving farther apart through space is that the math of general relativity describes it that way, and GR has been well-supported by experiments so far. GR is all about curvature of spacetime, and curvature of anything can be determined by how we measure distances. A lot of the math in ...

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The balloon analogy imagines the universe as a 2D surface expanding around a central point as it moves through a 3rd dimension of time. This may be the origin of confusion as in reality there is no 2D surface of expansion, like a wave front, but rather an expansion of 3D spacetime, wherein every point in space quite literally is its own central point from ...

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Your question may presuppose that the Universe had a beginning in its own past. If we apply the logic of our experience and perception that we live with in space/time, this may seem like a reasonable inference. But just as complex systems may need more than knowledge of the sum of their constituents to be understandable, broader knowledge of the Universe ...

4

I'll answer your question with an analogy. Imagine a really small balloon, so small that it occupies a point. Now, imagine that the balloon is expanding uniformly outward from that point. Note that that central point is not part of the balloon. It's the same idea as to what happened with the BB. In this analogy, the universe is the surface of the balloon. ...

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it must have started from a single point This is a common misconception popularized buy the media. Imagine this grid: Imagine each square getting larger. If you think about it, you will see that each point on the grid is expanding. The grid is the universe. Each point on the universe is its own "singularity".

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No, the argument is not correct. The spatial "conformal" coordinate $R$ in which, together with the conformal time $\tau$, the angle of the light rays is 45 degrees is not $\rho$ but nothing else than $r$: $$ds^2 = -dt^2 + a(t)^2 dr^2 = a(t)^2 (-d\tau^2 + dr^2)$$ If you want a diagram with $\tau$ on the vertical axis where the light rays are drawn at 45 ...

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Surely therefore our locally measured time is not the cosmological time t but rather the conformal time T? I don't think so. Our locally measured time is our locally measured time. If you had a clock that started ticking when the big bang occurred, the clock reading would be 13.8 billion years. If it displayed the conformal time, the clock reading would be ...

2

No. It is perfectly possible to have a flat universe that expands forever and is accelerating. Dark energy is what makes this possible. Whilst the curvature of the universe is defined by the sum of all the energy densities in it, the effects of matter (baryonic or dark) and dark energy are quite different on its dynamics. It is in fact quite possible to ...

1

Well, yes. "Expansion" of time as you call it is the cosmological age. The "direction" of progression of the time defines cosmological arrow of time.

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This is a commonly considered idea, of which one variant is the "Hubble bubble". Anything that happens outside of the visible universe, is, after all, in principle unknowable to us.

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Regular matter and energy, through, gravity tends to slow the expansion. I do not know of any theory that treats it or any other "retarding" force as friction. However there is evidence that another stuff in the universe, different from regular matter and energy (called dark energy) is actually accelerating the expansion, rather than slowing it (also, ...

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Gravity is the retarding force. I don't think that non-conservative forces are customarily considered.

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This is yet another instance of taking the ubiquitous balloon analogy too far. See, while it's a wonderful way to express the expansion of the universe, there are some misconceptions that arise from it: We live in a universe of finite size (we don't know, but we think not) and non-zero curvature (according to WMAP, we don't, or at least we think we don't) ...

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If you mean by "our universe" the matter in spacetime we are able to reach and observe then you are right. The universe will become more and more finite for us unless someone will invent a "warp drive" or "wormhole" (currently the probability for it is very low). According to research you have ca. 100bn years time before all others galaxies will be gone ...

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Galaxies are not moving away from us, it is the space between us and the galaxies (and everything, in general) that is continually expanding. This is allowed to happen faster than the speed of light, because no object actually crosses the light speed barrier in the process. So consequentially, the universe has no size constraint like the one you've stated.

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As pointed out in the answer above, the observations that lead to the dark energy theory were not all distant (7-14 billion light years), but less so. Dark Energy expansion is observed throughout much of the observable universe - not just the very distant. Also, consider the basic hubble discovery - galaxies 4 billion light years away were moving way from ...

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The thing is, we don't completely base our understanding of the expansion of space on galaxies 7 to 14 billion light-years away. For evidence that the universe is expanding, look at Edwin Hubble's original paper in which he confirmed what we now call Hubble's law. The galaxies he studied are on the order of millions of parsecs away. Multiply that by 3.26 to ...

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There is a concept known as entelechia, which basically means an idea so complicated and so full of border cases that no useful ideas can be obtained from it. One entelechia is the concepto of god, a súper being who created everything in just 6 days and who needs your money. And the fossil record was put there by good just to test your faith. Eventually it ...

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