The Universe is a Very Big Place

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The farther one will naturally appear dimmer. Scientists can compare a star's actual brightness with what we see from Earth and use that difference to calculate how far away the star is, Gallagher said. But what about the absolute edge of the universe? How do scientists calculate distances to objects that far away?

That's where things get really tricky. Remember: the farther an object is from Earth, the longer the light from that object takes to reach us. Imagine that some of those objects are so far away that their light has taken millions or even billions of years to reach us. Now, imagine that some objects' light takes so long to make that journey that in all the billions of years of the universe, it still hasn't reached Earth.

And what's outside of that? We don't really know," Kinney said. But by calculating the size of that little bubble, scientists can estimate what's outside of it. Scientists know that the universe is That means that an object whose light has taken You might be tempted to think that gives us an easy answer for the size of the universe: But keep in mind that the universe is also continuously expanding at an increasing rate.

In the amount of time that light has taken to reach us, the edge of the bubble has moved. Luckily, scientists know just how far it's moved: Some scientists have used that number to try and calculate what lies beyond the limit of what we can see. Based on the assumption that the universe has a curved shape, astronomers can look at the patterns we see in the observable universe and use models to estimate how much farther the rest of the universe extends. One study found that the actual universe could be at least times the size of the But Kinney has other ideas: "There's no evidence that the universe is finite," he said, "It might very well go on forever.

There's no saying for sure whether the universe is finite or infinite, but scientists agree that its "really freaking huge," Gallagher said. Unfortunately, the little part we can see now is the most we'll ever be able to observe. Because the universe is expanding at an increasing rate, the outer edges of our observable universe are actually moving outward faster than the speed of light. The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift.

Observations have found this to be roughly true, but this effect depends on cluster properties that do change with cosmic time, making precise measurements difficult. Future gravitational waves observatories might be able to detect primordial gravitational waves, relics of the early universe, up to less than a second after the Big Bang.

As with any theory, a number of mysteries and problems have arisen as a result of the development of the Big Bang theory.

Some of these mysteries and problems have been resolved while others are still outstanding. Proposed solutions to some of the problems in the Big Bang model have revealed new mysteries of their own. For example, the horizon problem , the magnetic monopole problem , and the flatness problem are most commonly resolved with inflationary theory , but the details of the inflationary universe are still left unresolved and many, including some founders of the theory, say it has been disproven.

It is not yet understood why the universe has more matter than antimatter. However, observations suggest that the universe, including its most distant parts, is made almost entirely of matter. A process called baryogenesis was hypothesized to account for the asymmetry.

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For baryogenesis to occur, the Sakharov conditions must be satisfied. These require that baryon number is not conserved, that C-symmetry and CP-symmetry are violated and that the universe depart from thermodynamic equilibrium. Measurements of the redshift — magnitude relation for type Ia supernovae indicate that the expansion of the universe has been accelerating since the universe was about half its present age. To explain this acceleration, general relativity requires that much of the energy in the universe consists of a component with large negative pressure , dubbed "dark energy".

Dark energy, though speculative, solves numerous problems. Dark energy also helps to explain two geometrical measures of the overall curvature of the universe, one using the frequency of gravitational lenses , and the other using the characteristic pattern of the large-scale structure as a cosmic ruler.

Negative pressure is believed to be a property of vacuum energy , but the exact nature and existence of dark energy remains one of the great mysteries of the Big Bang.

Therefore, matter made up a larger fraction of the total energy of the universe in the past than it does today, but its fractional contribution will fall in the far future as dark energy becomes even more dominant. The dark energy component of the universe has been explained by theorists using a variety of competing theories including Einstein's cosmological constant but also extending to more exotic forms of quintessence or other modified gravity schemes.

During the s and the s, various observations showed that there is not sufficient visible matter in the universe to account for the apparent strength of gravitational forces within and between galaxies. In addition, the assumption that the universe is mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the universe today is far more lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter has always been controversial, it is inferred by various observations: the anisotropies in the CMB, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and X-ray measurements of galaxy clusters.

Indirect evidence for dark matter comes from its gravitational influence on other matter, as no dark matter particles have been observed in laboratories. Many particle physics candidates for dark matter have been proposed, and several projects to detect them directly are underway. Additionally, there are outstanding problems associated with the currently favored cold dark matter model which include the dwarf galaxy problem [] and the cuspy halo problem.

The horizon problem results from the premise that information cannot travel faster than light. In a universe of finite age this sets a limit—the particle horizon —on the separation of any two regions of space that are in causal contact. There would then be no mechanism to cause wider regions to have the same temperature. A resolution to this apparent inconsistency is offered by inflationary theory in which a homogeneous and isotropic scalar energy field dominates the universe at some very early period before baryogenesis.

During inflation, the universe undergoes exponential expansion, and the particle horizon expands much more rapidly than previously assumed, so that regions presently on opposite sides of the observable universe are well inside each other's particle horizon.

The observed isotropy of the CMB then follows from the fact that this larger region was in causal contact before the beginning of inflation. Heisenberg's uncertainty principle predicts that during the inflationary phase there would be quantum thermal fluctuations , which would be magnified to cosmic scale. These fluctuations serve as the seeds of all current structure in the universe. If inflation occurred, exponential expansion would push large regions of space well beyond our observable horizon. A related issue to the classic horizon problem arises because in most standard cosmological inflation models, inflation ceases well before electroweak symmetry breaking occurs, so inflation should not be able to prevent large-scale discontinuities in the electroweak vacuum since distant parts of the observable universe were causally separate when the electroweak epoch ended.

The magnetic monopole objection was raised in the late s.

Structure and Composition:

Grand unified theories predicted topological defects in space that would manifest as magnetic monopoles. These objects would be produced efficiently in the hot early universe, resulting in a density much higher than is consistent with observations, given that no monopoles have been found.

This problem is also resolved by cosmic inflation , which removes all point defects from the observable universe, in the same way that it drives the geometry to flatness. Curvature is negative if its density is less than the critical density ; positive if greater; and zero at the critical density, in which case space is said to be flat.


  • The big bang is still happening, and we can see the universe expanding.
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  • Rooftop Rascals.

The problem is that any small departure from the critical density grows with time, and yet the universe today remains very close to flat. For instance, even at the relatively late age of a few minutes the time of nucleosynthesis , the density of the universe must have been within one part in 10 14 of its critical value, or it would not exist as it does today.

Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe were greater than the critical density , then the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state similar to that in which it started—a Big Crunch. Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down but never stop.

Star formation would cease with the consumption of interstellar gas in each galaxy; stars would burn out, leaving white dwarfs , neutron stars , and black holes. Very gradually, collisions between these would result in mass accumulating into larger and larger black holes.

What Is the Big Bang?

The average temperature of the universe would asymptotically approach absolute zero —a Big Freeze. Eventually, black holes would evaporate by emitting Hawking radiation. The entropy of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death. Modern observations of accelerating expansion imply that more and more of the currently visible universe will pass beyond our event horizon and out of contact with us. The eventual result is not known. This theory suggests that only gravitationally bound systems, such as galaxies, will remain together, and they too will be subject to heat death as the universe expands and cools.

Other explanations of dark energy, called phantom energy theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn apart by the ever-increasing expansion in a so-called Big Rip. The Big Bang as the origin of the universe: One of the common misconceptions about the Big Bang model is that it fully explains the origin of the universe. However, the Big Bang model does not describe how energy, time, and space was caused, but rather it describes the emergence of the present universe from an ultra-dense and high-temperature initial state.

The Big Bang was "small" : It is misleading to visualize the Big Bang by comparing its size to everyday objects. When the size of the universe at Big Bang is described, it refers to the size of the observable universe, and not the entire universe. Hubble's law violates the special theory of relativity : Hubble's law predicts that galaxies that are beyond Hubble distance recede faster than the speed of light.

However, special relativity does not apply beyond motion through space. Hubble's law describes velocity that results from expansion of space, rather than through space. Doppler redshift vs cosmological redshift : Astronomers often refer to the cosmological redshift as a Doppler shift which can lead to a misconception. Accurate derivation of the cosmological redshift requires the use of general relativity, and while a treatment using simpler Doppler effect arguments gives nearly identical results for nearby galaxies, interpreting the redshift of more distant galaxies as due to the simplest Doppler redshift treatments can cause confusion.

The Big Bang explains the evolution of the universe from a density and temperature that is well-beyond humanity's capability to replicate, so extrapolations to most extreme conditions and earliest times are necessarily more speculative. How the initial state of the universe originated is still an open question, but the Big Bang model does constrain some of its characteristics. For example, observations indicate the universe is consistent with being flat which implies a balance between gravitational potential energy and other forms requiring no additional energy to be created, [] [] while quantum fluctuations in the early universe can provide the circumstances for dense regions of matter such as superclusters to form.

Ultimately, the Big Bang theory, built upon the equations of classical general relativity, indicates a singularity at the origin of cosmic time, and such an infinite energy density may be a physical impossibility.

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In any case, the physical theories of general relativity and quantum mechanics as currently realized are not applicable before the Planck Epoch , and correcting this will require the development of a correct treatment of quantum gravity. While it is not known what could have preceded the hot dense state of the early universe or how and why it originated, or even whether such questions are sensible, speculation abounds as the subject of " cosmogony ".

Proposals in the last two categories see the Big Bang as an event in either a much larger and older universe or in a multiverse.

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