So we determine how long ago the big bang occurred by looking at the rate the universe is expanding...?

Question

...and reverse it.
However, if there are objects/bodies beyond our viewing range, how can we be sure about precisely dating the Big Bang? (Hopefully this makes sense). In other words, if we're unsure of the size of the universe, how can we use the rate of expansion to determine age?

Also, is it assumed the rate of expansion is (and has always been) constant?

Thx.

Answer 1

We can use the Cosmic Microwave Background (CMB) as a reference. This shows the early universe at the point where it became transparent. The elapsed time from the Big Bang to there has been calculated by theory. So in simplified terms, by knowing the red shift of the CMB, and the expansion rate of the universe, we can tell how long ago that happened. Recent, more precise estimates of the age of the universe use small variations in the CMB, in combination with theoretical models of the early development of the universe, to arrive at an age of 13.7 billion years.

Answer 2

To get an approximate age for the Universe, you don't need to see the whole Universe, you only need to see a few objects at different distances.

Answer 3

to answer the 2nd part, the latest research shows that the universe is expanding faster now than in the past. We have no way to account for this, but different teams have obtained the same results,

Answer 4

A number of different observations corroborate the Big Bang theory. Edwin Hubble (1889-1953) discovered that galaxies are receding from us in all directions. He observed shifts in the spectra of light from different galaxies, which are proportional to their distance from us. The farther away the galaxy, the more its spectrum is shifted towards the low (red) end of the spectrum, which is in some way comparable to the Doppler effect. This redshift indicates recession of objects in space, or better: the ballooning of space itself. Today, there is convincing evidence for Hubble's observations. Projecting galaxy trajectories backward in time means that they converge to a high-density state, i.e. the initial fireball.

According to the Copernican cosmological principle, the universe appears the same in every direction from every point in space, or in more scientific terms: The universe is homogeneous and isotropic. There is overwhelming evidence for this assertion. The best evidence is provided by the almost perfect uniformity of the cosmic background radiation. This observed radiation is isotropic to a very high degree and is thought to be a remnant of the initial Big Bang explosion. The background radiation originates from an era of a few hundred thousand years after the Big Bang, when the first atoms where formed. Another piece of evidence speaking in favour of Big Bang is the abundance of light elements, like hydrogen, deuterium (heavy hydrogen), helium, and lithium. Big Bang nucleosynthesis predicts that about a quarter of the mass of the universe should be helium-4, which is in good agreement with what is observed.

On basis of our understanding of the past and present universe, we can speculate about its future. The prime question is whether gravitational attraction between galaxies will one day slow the expansion and ultimately force the universe into contraction, or whether it will continue to expand and cool forever. The current rate of expansion (Hubble Constant) and the average density of the universe determine whether the gravitational force is strong enough to halt expansion. The density required to halt expansion (=critical density) is 1.1 * 10^-26 kg per cubic meter, or six hydrogen atoms per cubic meter; the relation "actual density" / "critical density" is called Omega. With Omega less than 1, the universe is called "open", i.e. forever expanding. If Omega is greater than 1 the universe is called "closed", which means that it will contract and eventually collapse in a Big Crunch. In the unlikely event that Omega = 1, the expansion of the universe will asymptotically slow down until it becomes virtually imperceptible, but it won't collapse.

Answer 5

I don't haev a concrete or correct answer or explanation for this question but I felt the need to say something becase of that idiot bernie. If you dont have any constructive thing to say dont bother opening your mouth at all.

and speaking about expanding, I think his brain (bernie's) hasn't expanded yet or maybe he just likes to act immature (if he is inside an age range to be considered mature of course which I highly doubt)

Answer 6

To get an approximate age for the Universe, you don't need to see the whole Universe, you only need to see a few objects at different distances. We can't see any objects with redshift higher than 1000, but their dynamics only effects the timing of the very early Universe. It is certainly true that those early times, earlier than a nominal 400,000 years after the Big Bang, might really change things. Actually, we probably understand the dynamics of the Universe after the first second, because if they were very different from the standard theory, light element nucleosynthesis would not come out correctly. However, the period of "early inflation", nominally in the first tiny fraction of a second, is not at all understood, and it is possible to invent a theory of early inflation that makes the past history of the Universe infinite. In other words, it is possible that early inflation actually lasted an infinite amount of time, rather than a tiny fraction of a second, making the age of the Universe infinite ("ongoing eternal inflation"). It would still be true that the time since the nominal "first second" (when the light elements were generated) is 13.7 billion years, but the "bang" itself would be in an infinite past of complex, unknown high-energy physics.

It is definitely not true that the rate of expansion is constant---if it were, you would only need the distance and redshift of a single object, and the age of the Universe would then be the distance to that object divided by its velocity. Instead, the age of the Universe is determined by fitting an entire self-consistent dynamical model of the Universe, including the time-dependent gravitational effects of all the various constituents (baryonic matter, dark matter, dark energy, relativistic particles). The net gravitational effect of the photons, for example, is less important now than it was in the early Universe, and this can be calculated. The Dark Energy was not important in the distant past, but is becoming increasingly important now. The problem with the very early Universe is that we don't understand the properties of materials under the extremely high densities and temperatures of those very early times, and they might be very different from what we expect.

Answer 7

this is not nessasary because the rate of the expansion of the universe could have increased at some point in time so if u reverse it u may find the date earlier that it actually is u do not what rate it fully has expanded like my ars*hole has expanded dramtically over the years as yours becuase u now get bummed alot longer and quicker than before