From the Big Bang to the Big Rip

General physics and astronomy discussions not directly related to Celestia
Spaceman Spiff
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Post #21by Spaceman Spiff » 01.10.2005, 11:24

I think it's fine to start a discussion of cosmology in this forum by inviting people's ideas about it because cosmology is a part of astronomy (though it should be the other way around :) ).

You asked for theories, but the problem then arose through that with science. It's not just that some people weren't being properly scientific (because you don't have to be just to raise or discuss an idea) but that some thought they were being scientific when they weren't.

I see my ramblings about the scientific method fell on blind eyes...

WildMoon wrote:Theory:

Big Bang Theory suggests ... [snip]

Law:

The Law of Conservation states ... [snip]

Hypothesis:

I think that ... [snip]

A nice attempt from a young 'un to formalise things, but not right enough I'm afraid ;).

A theory by modern standards must make precise predictions which can be tested, and the tests should be aimed to disprove the theory, not prove it. That's because there's an asymmetry in logic concerning proof and disproof, as Hume noted. The best way to make precise predictions is using mathematics, because mathematics is the most precise form of communication known to us.

A law is a misnomer for a theoretical prediction. There is actually no such thing as a natural law. The name came from ancient Greek philosophers who supposed that some god or gods commanded nature to obey their laws (and that means that's why they thought things did what they did: divine control). However, whereas people can break legal laws and get punished, for natural laws we end up with the silly situation that we change our natural laws to fit what nature does. So, can a natural law ever really be broken?

Hypothesis comes from ancient Greek; 'below a position', meaning less than a firm idea. Hypotheses are then propositions, explanations or assumptions specific to some problem, For example, concerning the causes of Californian forest fires, I could propose these hypotheses: a) lighting strikes, b) human campfires, c) Flambus, god of fires and lollipops. They are possibilities.

The example you gave about plants A and B is actually rather more suited to scientific theory, though not quantitative, let alone mathematical. You predict plant A will grow faster because of better nutrition - it's clear enough to turn it into a mathematical matter: the mass of plant A should be greater than that of plant B. Most people make the mistake of thinking that if you measure plant A to be heavier than plant B, you have 'proven' your theory: nutrtion helps plants grow more. Not true. Plant A could have grown more because of a different reason. Any different reason. The interesting outcome is if plant A did not grow more than plant B. Then you know that the nutrition did not cause plant A to grow more.

When we talk of a 'hypothetical planet' that means something that 'could be' but is not proven. However, I have mentioned the problem of proof, as in...

Malenfant wrote:It is important if there is some way that the hypothesis can be proved or disproved. If it's unprovable, then it's a waste of time.

Malenfant wrote:NO. It's not like that at all.

Theories have sufficient evidence to support them ... [snip]


... which looks like the Francis Bacon description of the scientific method, which is flawed with the problem of induction.

Spiff.

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Hunter Parasite
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Post #22by Hunter Parasite » 01.10.2005, 11:40

grrrrr... I know what the difference between a hypothosis and a theorie. I hate when my boards come of topic.... I just wanna strangle someone right now! :evil:

Malenfant
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Post #23by Malenfant » 01.10.2005, 16:46

Spaceman Spiff wrote:... which looks like the Francis Bacon description of the scientific method, which is flawed with the problem of induction.


Well, you prove (or disprove) a hypothesis with repeated experiments, not just a single experiment. Either way the point is that you require evidence to show whether the hypothesis is valid or not. I'm not disagreeing with you though, I probably just wasn't phrasing things as clearly as I'd have liked to.

Spaceman Spiff
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Post #24by Spaceman Spiff » 01.10.2005, 17:57

Hunter Parasite wrote:
grrrrr... I know what the difference between a hypothosis and a theorie.


Yes, but I was addressing WildMoon. By the way, you should also know how to spell theory by now ;) (No no! Pwease don't stwangle me! I'm only twying to hewlp!

Hunter Parasite wrote:
I hate when my boards come of topic...


I'm afraid you'll have to get used to that. It happens all the time, and not just here: it's a phenomenon associated with all discussion forums on the electronical interweb.

Anyway, did anyone see the football match last night?

Malenfant wrote:Well, you prove (or disprove) a hypothesis with repeated experiments, not just a single experiment.


Yes, that's how Francis Bacon described the scientific method, but Hume knocked it and Popper replaced it: you can't ever prove a hypothesis, only disprove it. I'm noting that you're (correctly) summarising the 'classical' scientific method of Francis Bacon, rather than the new 'Popper' method.

Do you know the white swan, black swan problem?

Spiff.

Spaceman Spiff
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Post #25by Spaceman Spiff » 01.10.2005, 18:04

Oh yes, I forgot to add, Hunter Parasite:

It seems to me either the Universe collapses and returns to a state similar to which it began, or it expands forever and eventually each locale turns effectively into a 'perfect' vacuum', which I understand might lead to a Big Bang.

Here's a problem though. If humanity does make it into colonising space, and even survives the death of Earth and Sun in five billion years time, then could we go on to solve all problems that threaten our continued survival? Could we survive the end of our Universe, whether by Big Crunch or Heat Death? Could we enter strange universes or create new universes for us to enter?* Could we survive forever?

Spiff.

* Read Excession by Iain M Banks.

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Hunter Parasite
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Post #26by Hunter Parasite » 02.10.2005, 13:09

I spelled theorie uh theory wrong Noooooooo!!! The worlds gonna exlpode!!! 8O

WildMoon
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Post #27by WildMoon » 03.10.2005, 00:50

Heat Death? I thought if the universe continued to expand and not go Big Crunch (for some reason I'm hoping it'll go Big Crunch) then all matter will just decay, all black holes will evaporate and all there will be is nothingness and the occasional one particle every hundred thousand lightyears...

No we will not survive forever (DOH!) which sucks. Oh well, life goes on (for some other species.)
Pi does not equal 3.14159265, it equals "yum!"

A world without Monty Python, gnomes, news crews that make a big deal out of a celebrity breathing, Star Trek, & Coca-Cola? That is impossible! IMPOSSIBLE!

eburacum45
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Post #28by eburacum45 » 03.10.2005, 18:46

I am fascinated by this discussion of inductive logic and Popperian falsification, but I am also interested in a discussion about the end of the universe, so let's get back to that.
The Heat death of the universe is really the same scenario as the one you describe, Wild Moon' when the universe has spread out to the extent you describe then the universe will have a very even temperature, which is what is generally called heat death. As there are no more temperature gradients then no more work can be done and the useful life of the Universe is over.

Of course two other possibilities have been mentioned, the Big Crunch (where the universe collapses back upon itself)
and the Big Rip (where the acceleration of the expansion of the Universe continues to accelerate at an increasing rate, eventually ripping the galaxies, stars, planets and atoms apart.)

The Big Crunch has been rejected by many cosmologists, mostly because of the apparent acceleration of the expansion of the universe.
The Big Rip has some adherents, but the last estimate I heard of a possible date for this event was many tens or hundreds of billions of years from now.

As Spm. Spiff said, the Heat Death scenario 'might' lead to a completely empty universe, which 'might' eventually undergo another Big Bang at some fantastically distant time in the far future.

But I am not sure how that would fit in with brane theory or superstring theory etcetera...

Oh yes; there is Andrei Linde's strange theory about the universe budding baby universes off during its lifetime; if that is possible then it might be possible to escape the fate of an individual universe by slipping into another.

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Hunter Parasite
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Post #29by Hunter Parasite » 03.10.2005, 23:35

eburacum45 wrote:Oh yes; there is Andrei Linde's strange theory about the universe budding baby universes off during its lifetime; if that is possible then it might be possible to escape the fate of an individual universe by slipping into another.


the going to another universe leads back to my Universal rift theorie in the 'theory talk with wildemoon' board http://www.shatters.net/forum/viewtopic.php?t=7909&start=15&sid=6a563c53d4c858584b71a4173387400c (i always spell theorie, i mean theory wrong)


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