# Tag Info

70

Actually, what you've read about the production of nuclei is not quite correct. There are several different processes by which atomic nuclei are produced: Big Bang nucleosynthesis is the fusion of hydrogen nuclei to form heavier elements in the early stages of the universe, as it cooled from the big bang. There are rather specific thermal requirements for ...

29

The key word in what you've heard is "available" because there is quite a lot of lithium in the earth that is not so easy to obtain. The notion of "available Lithium" probably means known land reserves, which according to this page amount to 14 million tons. The amount dissolved in seawater is estimated at 230 billion tons (which is enough for lots of ...

27

Spencer's comment is right: we never "prove" anything in science. This may sound like a minor point, but it's worth being careful about. I might rephrase the question like this: What's the smallest size of the Universe for which we have substantial observational evidence in support of the standard big-bang picture? People can disagree about what ...

27

There are quite a few common misconceptions about the expansion of the universe, even among professional physicists. I will try to clarify a few of these issues; for more information, I highly recommend the article "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" from Tamara M. Davis and ...

23

An observer with zero comoving velocity (i.e. zero peculiar velocity). Such an observer can be defined at every point in space. They will all see the same Universe, and the Universe will look the same in all directions ("isotropic"). Note that here I'm talking about an "idealized" Universe described by the FLRW metric: \mathrm{d}s^2 = ...

22

The cosmic microwave background does not originate with the big bang itself. It originates roughly 380,000 years after the big bang, when the temperature dropped far enough to allow electrons and protons to form atoms. When it was released, the cosmic microwave background wasn't microwave at all- the photons had higher energies. Since that time, they have ...

19

The big bang was everywhere, because distance didn't exist before it, so from one perspective, everywhere may be the centre (especially as some theorists think, the universe doesn't have an edge) The real issue is that the question shouldn't matter, as we can only gain information from distances within our visible radius and once we get to that limit, what ...

19

This is a common point of confusion, not only with regards to inflation, but any time an expanding universe comes up... The "cosmic speed limit" as you call it says that no particle or signal can move through spacetime faster than the speed of light. Spacetime is a very specifically defined thing, described with a coordinate system. There is no restriction, ...

16

General relativity is a local theory. That means it describes spacetime near the point you're looking at but it doesn't say anything about the large scale structure of spacetime. Now this may seem unrelated to your question, but actually it's key to why we say that time started at the Big Bang. If we make a few apparently sensible assumptions about the ...

15

I work with stellar models, so I thought I'd chip in here. My instant reaction is that you shouldn't worry too much: determining the age of a star is difficult and different models will disagree (sometimes significantly!) on that age. How reliable is this research? I can't see an obvious reason to doubt the conclusion. What method do they use to ...

15

There's a very common misconception that the Big Bang happened at a point like a bomb going off. It doesn't help that almost ever TV documentary on the subject represents the Big Bang in this way. Explaining what actually happened is hard without going into the Maths, but here's an explanation I gave taken from (of all places) the Science Fiction Stack ...

14

It is not possible to calculate the coordinates of the point where the Big Bang happened, because there is no such point. All of space is expanding away from the rest of space, in a manner that looks the same throughout space (the technical term is that the universe is homogeneous). The Big Bang happened everywhere in space.

12

Here is a copy of an answer I wrote some time ago for the Physics FAQ http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html Is the Big Bang a black hole? This question can be made into several more specific questions with different answers. Why did the universe not collapse and form a black hole at the beginning? Sometimes people find ...

11

Short answer: They are different. Long answer: There are a number of subtleties involving horizons in cosmology. I refer anyone who is interested in the details to a paper by Davis and Lineweaver, which I have referenced many times on this site. Here I'll only refer to Figure 1 of that paper, shown below. All three frames are the same, with the lower two ...

11

In the expanding universe, you have to be a bit careful to define exactly what you mean by distance. The "proper distance" referred to here in that article means the distance measured at the present time. We have to be careful even to define what we mean by that last phrase -- time is relative, you know. But if the universe is approximately homogeneous, then ...

11

This is actually a common question. Many websites have been setup to try to explain this. I like this one for instance. I shall attempt to do my own layman explanation. First of all, in order to have a black hole, you need to have a place for it to be in. Since there was no such thing as a universe, there isn't a place for the black hole to actually ...

11

Yes, the expansion of space itself is allowed to exceed the speed-of-light limit because the speed-of-light limit only applies to regions where special relativity – a description of the spacetime as a flat geometry – applies. In the context of cosmology, especially a very fast expansion, special relativity doesn't apply because the curvature of the spacetime ...

10

A high enough energy density is a necessary condition but not a sufficient condition for black holes to form: one needs to have a center which will ultimately become the center of the black holes; one needs the matter that collapses to the black hole to have a low enough velocity so that gravity may squeeze it before the matter manages to fly away and dilute ...

10

It comes from everywhere. The thing is that the Big Bang didn't happen at an isolated point and expand into existing space. Space was compact then and has grown bigger in the intervening time.

10

You'll see it clearly in this two images: As you can see, I've only moved one layer, while the other stays static.This is a clear example what happens in the universe. Everywhere is the "center of universe".

10

What you are describing looks like a hypothesis to me. A hypothesis is an idea. You have an idea. A theory, in the sense it is used by modern physics, is an idea about how the universe works which is supported by some rigorous elements, whether we're talking about some mathematical explorations (such as in the case of string theory, or back in the day, ...

10

What you're seeing is the galactic plane of the Milky Way. There are several processes emitting at a variety of wavelengths, and because the emission is so nearby it comes out quite bright on the all sky map. Planck observes at about $\mathrm{mm}$ wavelengths, so the most prominent emission within the galaxy is thermal emission from dust clouds. Often maps ...

9

Good question! I often pondered that myself. As this website explains, the Big Bang wasn't a black hole basically because it couldn't be! A black hole is the mathematical solution to Einstein's equations of General Relativity that describes a pre-existing region of spacetime that has gravitationally collapsed and formed a singularity. Since there was no ...

9

This is a small complement to David's and Scott's answers As usual Wikipedia's page on Lithium contains useful information : Both natural isotopes have anomalously low nuclear binding energy per nucleon compared to the next lighter and heavier elements, helium and beryllium, which means that alone among stable light elements, lithium can produce net ...

9

Yes, the energy conservation law fails not only right after the Big Bang but in any cosmological evolution. See e.g. http://motls.blogspot.com/2010/08/why-and-how-energy-is-not-conserved-in.html The time-translational invariance is broken, so via Noether's theorem, one doesn't expect a conserved quantity. Also, if one defines the "total" stress energy ...

9

Of course the expansion of space is being considered by astronomers. In fact, it's pretty much the only thing they are considering. The redshift due to expansion of space is the way that astronomers know that it came from 13.14 billion years ago. What you do is look at the lightwaves very carefully. They will be stretched out (which looks like redshifting) ...

9

Omar is correct that the furthest back we can "see" is the Cosmic Microwave Background because before this time photons, the carriers of light, were "coupled" with the protons and neutrons (and before that quarks). As the universe cooled the photons were able to be freed and create the Cosmic Microwave Background we see today. However we can theoretically ...

9

If the Universe is spatially infinite, it always had to be spatially infinite, even though the distances were shortened by an arbitrary factor right after the Big Bang. In the case of a spatially infinite Universe, one has to be careful that the singularity doesn't necessarily mean a single point in space. It is a place - the whole Universe - where ...

Only top voted, non community-wiki answers of a minimum length are eligible