Universe

[jflowers]

I've seen that quote in someone's signature.

Yes, lots of Douglas' quotes around, my location for example

[Vince1963]

I've seen that quote in someone's signature.

Yeah you have Ganymede12 :icon_mrgreen: :icon_mrgreen: :icon_mrgreen: . I think you'll find its "Astrosurf" LOL

[Naemeth]

So I've a question, how does the fusion of Hydrogen make Helium, and from that every element in the Universe, when in chemical forumlae at least, Hydrogen isn't in every chemical. Is this because the Hydrogen has changed, and if it is, how has it changed?

[SionR25]

Each element is defined by he number of protons it has within its nucleus. Hydrogen is the most basic element and only has one proton. In extreme pressures and heat of a star, two hydrogens (two protons) are forced together to make helium, which has a proton number of two. This process is the same for all other elements, just greater number of protons being forced together.

It isn't a chemical process hence not every element is shown to contain hydrogen.

Sion

[JulianO]

Its changed, its not a chemical reaction but a nuclear reaction.

Chemical reactions involve the electrons around the nucleus shifting positions and forming attachments between two atoms.

Nuclear reactions involve the changing of constituent particles that form the nucleus of the atom.

So Hydrogen - in its normal form is a nucleus composed of a proton, with a single electron around it.

In a star it is normally ionised, meaning the electron has been stripped away by the heat.

Normally two hydrogen nuclei, being protons and having the same charge repel each other, but if they are hot enough, and so moving fast enough they can come close enough despite the repulsive electric charge for the two to come under the influence of a different short range force that will stick the two together. Its more complicated than that, as actually one of the protons has to change to a neutron.

Anyway - through a series of nuclear reactions, basically 4 protons come together to form a helium nucleus, composed of two protons and two neutrons (+ various other particles to balance the books). This releases some energy, which makes the sun shine.

There are other reactions in bigger stars that can fuse 3 Heliums together to make carbon. Suffice it to say you need temperatures similar to the middle of the sun (15 million degrees or so) to even begin this process, so not the sort of thing you'd do in a chemistry lab!

[Naemeth]

Each element is defined by he number of protons it has within its nucleus. Hydrogen is the most basic element and only has one proton. In extreme pressures and heat of a star, two hydrogens (two protons) are forced together to make helium, which has a proton number of two. This process is the same for all other elements, just greater number of protons being forced together.

It isn't a chemical process hence not every element is shown to contain hydrogen.

Sion

Cheers for that!

If we managed Nuclear Fusion to the extent we could use it as our own secondary fuel source (primary being our own Sun), wouldn't we be creating a sun in miniature?

[SionR25]

Yep, thats the idea. Its the biggest source of energy we know so the best thing to try and recreate to meet our own energy needs.

Sion

[symesie04]

Fusion is highly effecient and clean source of energy. Perfection of it would almost entirely relieve us of our dependecy of fossil fuels. Perhaps its no wonder then that total global govermental funding into research is less than $10,000,000 a year. Pathetic.

[Naemeth]

I'm sure the NHS spending alone is 8 times that.

[symesie04]

Think Posh Spices and Coleen Rooney's joint annual spending is 8 times that as well! (allegedly)

[George Jones]

I think it is, or at least in the way if you could shoot off in one direction at enough speed and travel for long enough you will not ever get to an 'edge' of the universe but will eventually arrive back at the same place.

We can only arrive back at the same place in space if the universe is spatially closed. If space were 1-dimensional and closed, space would be the circumference of a circle. The circumference of a circle is 1-dimensional, and if you travel on the circumference of a circle, you can back to where you started without turning around. If space were 2-dimensional and closed, space would be the surface of a sphere. The surface of a sphere is 2-dimensional (e.g., the surface of the Earth), and if you travel on the surface of the Earth, you can back to where you started without turning around.

In our universe, space is 3-dimensional, so one more dimension of space must be added. This is hard to imagine, because there is no fourth dimension of space (time is not a fourth dimension of space) that we can use to visualize a closed 3-dimensional curving around in. This just a problem with visualization, not an actual impediment to maths and physics.

The latest results show the universe is flat, at least pretty much so. WMAP results indicate it is flat within an error of 0.5%. So if you would never come back to your starting point.

Is our universe closed? As Julian has noted, if it is closed, it is just barley closed. Can we, in principle, cirmumnavigate our universe if it is just barely closed? This is a question that I have been meaning to look at for several years, and this thread has finally motivated me to get down to it. Thanks! My calculations indicate that in a universe similar to ours that is 1% over the critical density for being closed, light only makes it 7% around the circumference of such a closed universe. This may seem strange, since, even if our universe is closed, observations indicate that our universe will never end in a Big Crunch. Light has all of eternity to circumvate a closed universe, but it only make it 7% of the way around! Why? Because: 1) if our universe is closed, it is only just barely closed; 2) the universe is expanding. A long-winded expansion on this follows.

Standard models of the universe are either open or closed. The average density of matter and energy determines if a universe is open or closed. If this density is at or less than a critical density, the universe is open; if this density is greater than the critical density, the universe is closed. Here, "open", "closed", and "flat" all refer to 3-dimensional space, not to 4-diemsional spacetime. A flat universe is actually a curved 4-dimensional spacetime. In Einstein's theory of gravity, gravity is spacetime curvature, and universes have gravity. A flat universe is an open universe that is on the border of being closed, i.e., right at critical density.

Standard models of the universe either expand forever, or reach maximum expansion, contract, and end in a Big Crunch.

Without dark energy, the preceding two paragraphs are linked. A universe expands forever if and only if it is open; a universe ends in a Big Crunch if and only if it is closed. Without dark energy, a photon circumnavigates a closed unicerse exactly once during the time from Big Bang to Big Crunch.

Dark energy, repulsive gravity, changes the picuture. With dark energy, closed universes can still end in a Big Crunch if the density of dark energy is small enough, but, because of repulsiom, the time taken to get to Big Crunch will be longer. Consequently, a photon in this type of universe will circumnavigate the universe more than once. with just the right amount of dark energy, a photon can circumnavigate the universe an arbitarily large number of time before the Big Crunch.

If, however, the amount of dark energy is large enough, a closed universe will expand forever, and, at late times, expansion will proceed exponentially quickly. Because of this exponential expansion, the position of the photon in space approaches a limiting value as time gets large. Depending on the amount of dark energy, this limiting position can be made arbitrarily small (lots of dark energy, early onset of exponential expansion) or arbitrarily large.

My calculations seem to verify all this. As I said above, in a closed universe that fits our obseevations, a the limiting value is about 7% of te circumference of the universe.

Observations indicate that our universe is near the border between open and closed, and that even if our universe is closed, it will expand forever.

[Vince1963]

Hi guys... Just found this video on youtube

, weird coincidence or what, i didn't see this when i started this thread.

[Ganymede12]

So 10 pages of complete science talk -some of which made our heads hurt- has been explained in a 6 min YouTube video?

[Vince1963]

Great stuff Ganymede12... I feel a bit of a wally now lol. Its been a good thread though and i for one have definitely learned some stuff here, so not a complete waste of time.

[sologuitarist61]

I think all mpodern thinking

But isn't this true, that some scientists believe that this could be the case?. that black holes defy all physical laws, and could black holes just be the curved fabric of space (Albert Einstein) with no actual opening or exit (like water going down a plug hole but with no actual exit)(i'm not very good at explaining this) where all matter collects going round and round the vortex adding to the mass creating ever more energy...Till one day (who knows) it implodes on itself (big bang) creating the birth of a new universe maybe parallel to the one we know maybe there's others. maybe this is where we started from and its a continuous cycle.. We may never know. I'm sure you may have an answer for me Badgerchap lol

I think that all modern laws and thinking go out of the window when we talk about what it may be like inside a black hole. Plenty of ideas but I guess that is we will will ever have until someone goes in and comes back out (I know - impossible). The most likely scenario is that someone will come up with an idea that no one can see any fault in and that will be the new dogma.

[Ganymede12]

After watching the What's the Universe expanding into? clip, one of the other video's that came up was What is the Higgs Boson? I was interested and played the clip and it explained that the Higgs Boson makes up the Higgs field that gives matter mass. But...

• This contradicts what my physics teacher told me. He said that the Higgs boson is one step down from quarks and that they are truly the smallest thing that exists.
  
• If the Higgs field is every where then doesn't that mean the near vaccume of space isn't a vaccume at all and therefore sound should be able to travel through it?
  
• If the Higgs field is every where then that means that, as the Universe expands the number of Higgs bosons has to increase to fill the entire universe or the Higgs field is thinning out or the Higgs field doesn't cover the entire universe.
  

Once again, I am confused!

[DarkStar7]

As the Universe expands I expect the number of Higgs bosons to increases but each one doesn't last very long.Perhaps the aftermath of some of them appear as cosmic rays.

I was predicting the Higgs wouldn't exist. Even now I don't thing it will be found to have spin 0. My hypothesis which suggests we are within a hyper dimensional Universal gravitation field would need the Higgs field to be the 4D space-time turning into the 5th dimension. The Higgs field requires a boson, and my hypothesis requires a boson too,mine is the graviton. It's fantastic because very soon we will have the spin of the Higgs measured... Remember me when they say it's spin 2 please.

[Vince1963]

Very true Richard, I'm with you on that.

[Groucho Ben]

Hi, in trying to answer to the original post, I myself am utterly incapable of explaining it, so why not let a top-class theoretical physicist explain it instead?

Lawrence Krauss is a great public speaker, and really knows his stuff. The talk considers modern cosmology, as it pertains to the notion of a universal constant, closed/open universe models, darkmatter, etc, all in a manner very friendly to the layman.

in response to the 'but science doesn't 'know' much, it's just theory' position, Krauss also puts into relief just how much we do now know, which is a brain-blendering amount.

... Hope it's useful!