# Tag Info

4

Here is a good basic summary of the history of the steady-state theory and the observations that caused it to fall out of favor, mainly the second two mentioned by Kyle Kanos. One of these was the observation of intense radio sources that didn't seem evenly distributed throughout the universe, but were only seen at large distances (higher redshifts): The ...

2

The following passage has been extracted from the book Parallel worlds: Finally, in Nature magazine in 1965, Hoyle officially conceded defeat, citing the microwave background and helium abundance as reasons for abandoning his steady state theory.

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The steady state theory fails to model a few observed features of the universe: the accelerated expansion of the universe radio galaxies and quasars that are only observed at high redshifts & not everywhere the existence of the microwave background light

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Ever heard of the cosmic microwave background? The CMB is a relic from when the universe became "opaque" - when, as Wikipedia says, protons and electrons combined to form neutral atoms. These atoms could no longer absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog. So photons decoupled and the CMB was ...

-1

In a flat/Euclidean, isotropic, and homogeneous, Riedmann Universe, such as what we believe our own to be, space is infinite. This can be determined by solving the FLRW Metric with a curvature of $k=0$. The FLRW Metric for polar coordinates can be written as: $$ds^2 = -dt^2 + a^2(t) \left[ \frac{dr^2}{1 - kr^2} + r^2d\Omega^2 \right]$$ Since $r$ is the ...

2

Your questions are in no way challenging. The answer to both questions is the same: it could be, we do not know. Actually, you could also ask the opposite: how do we know that physical space is equivalent to the continuum (the real line) instead of being a larger infinite (by this a mean an ordered field of larger cardinality, such as the surreal line)

0

Thus, the two primary options for flat finite space "shapes" are 3-D torus or video-game-screen. Not true. It's possible that the universe has a nontrivial topology, but there is no evidence for it, and it's not the most common assumption. The most common assumption is that if the universe is closed, it has the topology of a 3-sphere. I do not ...

3

The total energy of the universe is a vexed issue since different commentators have different views about what the concept means. See the question Total energy of the Universe for a sampling of the various viewpoints. If you Google for zero energy universe you'll find several papers purporting to show that the total energy is zero. However since their ...

4

All statements like "when the universe was the size of a grapefruit" refer to the currently observable universe. As the universe has a finite age and light travels at a finite speed (and there is nothing infinite going on with expansion), the observable universe is a finite patch. I discussed some of the different notions of horizons in answering another ...

3

If we take the simple approach of determining the state of the "jerk" today by assuming an exponential expansion (e.g., $a(t)\sim\exp(H_0 t)$), then $$\dot a=H_0a\tag{1}$$ The derivative of this is then, $$\frac{d^2a}{dt^2}=H_0\dot{a}=H^2_0a$$ And now for the "jerk," $$\frac{d^3a}{dt^3}=H^2_0\dot{a}=H^3_0a\tag{2}$$ The Hubble constant is already pretty ...

2

At what speed does our universe expand? This question doesn't make sense in the form in which it was posed. To see why, let's start by thinking about how we know the universe is expanding. The expansion of the universe was originally discovered by Lemaître and Hubble, who found that the redshifts of galaxies were proportional to their distances from ...

0

As I stated in my comment, our observable universe is much larger than the Hubble radius: we can observe galaxies that are receding from us faster than the speed of light. I refer to this post of mine and links therein for more info: http://physics.stackexchange.com/a/63780/24142 Also, in the standard cosmological model, where the density of dark energy is ...

1

As mentioned in a comment, the observable universe is finite. However, it is reasonable to think that the total universe may be infinite. Although we don't know this for certain, there is no experimental evidence that definitively contradicts that (eg. the curvature of space is very close to zero, within the precision of our measurements). In fact, Brian ...

1

Ulitimately the Universe's expansion is due to the initial conditions, unfortunately explaining why these initial conditions exist is beyond the scope of classical big bang theory as they exist as parameters than can be adjusted. However the expansion of the Universe is not independent of the matter it contains and the Friedmann equations link the rate of ...

3

The basic reason for cosmological expansion is simply inertia. Because the universe was in an expanding state soon after the big bang, it kept expanding. This is roughly analogous to Newton's first law of motion. In addition to this, dark energy is currently causing a significant acceleration of the expansion. (Its effect was not dominant in the past, and ...

0

You are apparently comparing with the expansion of some object, which is being heated. Well, such an object consists of particles, atoms in a lattice maybe, and each of those vibrate. More thermal energy makes them vibrate more violent, which make them fill more space. If all atoms require more space, the object expands, since they all "push" at each ...

1

This sounds a bit in the spirit of John Wheeler's geometrodynamics. He hoped to find in the dynamic geometry of GR a way for "mass without mass, charge without charge, field without field" to somehow emerge just from vacuum gravitational fields interacting. He contemplated "geons" which would be packets of gravitational waves held together on the short ...

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Your question has been addressed before, see the questions: Can we observe an edge of the universe? Does the universe have an edge/boundary/barrier? If yes, what is at the edge? But this is a subtle issue and one that's worth using a few more of the Physics SE's electrons to discuss. You describe the universe as a bubble or a torus, and the implication ...

2

There is no edge of the universe. The standard model for cosmology is based on the FLRW metric. It is what happens when you assume the universe is homogeneous and apply general relativity. In this model the universe could have a finite volume that's not growing too fast, where paths just loop back on themselves. A photon in such a universe would keep ...

0

Will an unhindered (un-scattered) photon go to the edge of the universe? To add to the answer of @RedAct : If you are thinking of the three dimensional part of the universe we observe now, it is an instantaneous universe, i.e. time t has one value. In this sense we are at the edge of the expanding universe, the right cutoff at 13.8 billion years in the ...

1

The answer probably depends on how that question is interpreted. The universe is expanding. The ultimate fate of the universe isn't known for sure, but the growing consensus among cosmologists is that the universe will probably continue to expand forever. If that's the case, then a photon that leaves the Earth now will never catch up to what is currently ...

1

You presume causality, namely that something has to occur to instigate something else (cause and effect). In fact, you presume that there is a well-defined "time". However, our current best theories have problems defining time close to the start of the universe. If there is no clear way to define time then you cannot say that something has to precede ...

0

Your question is most right. But if we live in a 3d world not just a sheet because a sheet as you would say it has a bottom but what about the 3d vision of it don't you think it has a top and bottom and sides, just take a round ball and wrap a sheet around it add gravity to it and we really don't have a sheet but that only a visual complex of ones ...

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Have a read through Did the Big Bang happen at a point? and the answers to it. The singularity at the Big Bang is the zero time limit of the equation (the FLRW metric) that describes the expansion of the universe. Most physicists believe that this is a mathematical artefact and does not describe what actually happened. It seems likely that some quantum ...

4

Counter Argument - A better part of the universe seems to be governed by certain laws (of Physics), which appears to preclude a Divine Creator. In fact, sometimes with such a precision that one expects that even those aspects that aren't well understood today, would be well understood some day, when issues with existing theories get resolved/ these theories ...

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