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Author Topic:   How did the Aborigines get to Australia?
RAZD
Member (Idle past 675 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 61 of 226 (647055)
01-08-2012 12:05 AM
Reply to: Message 59 by foreveryoung
01-07-2012 7:19 PM


decay rate vs decay energy
Hi foreveryoung,

See Message 91 on Are Uranium Halos the best evidence of (a) and old earth AND (b) constant physics? for my reply

Enjoy.

Edited by Zen Deist, : mid not tid

Edited by Zen Deist, : moved off-topic post


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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Coyote
Member (Idle past 1376 days)
Posts: 6117
Joined: 01-12-2008


(3)
Message 62 of 226 (647057)
01-08-2012 12:13 AM


And now for something on topic
How did the Aborigines get to Australia?

They walked, sailed, waded and/or swam, arriving in Australia some 40,000 to 50,000 years ago, or earlier, after leaving Africa some tens of thousands of years previously.

The evidence we have on this comes from archaeology, genetics and related fields.

This evidence has nothing to do with any mythical floods, nor with decay rates for that matter.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

  
NoNukes
Inactive Member


Message 63 of 226 (647066)
01-08-2012 1:00 AM
Reply to: Message 60 by RAZD
01-07-2012 9:13 PM


Re: rapid decay knock-down
Fine. I was using action while you are using state, but we can use enriching for clarity to reduce confusion. The point is the same.

Not so fast with the dictionary. I didn't stop with the noun/verb issue. That would have been pedantic. I also provided, from the same reference that you are using, evidence that enrichment is also used to refer to the degree of the enrichment of fissile material and not merely as the name of the process or state.

What did you think the wikipedia article meant when it referred to an enrichment of 80 percent? Is it your opinion that such usage is incorrect?

That does not mean that you have worked through the question of what you need to do to increase the rate of decay, and then determined how that affects the rest of the (atomic) world.

Are you claiming to have done so? I'm going to return to this question at the end. I'll just note here that I don't see that you have actually made an argument that addresses this point. Instead you have asserted effects that result directly from an increased fission rate. And some of those assertions are demonstrably wrong. I'll deal with those first.

I am in fact familiar with the factors that are required to allow a sustained chain reaction, and your posts suggest that you are not. Increasing the number of source neutrons alone without increasing the percentage of those neutrons that cause fission will not result in criticality. In fact the lack of a suitable source of neutrons for starting a chain reaction is a problem that we dealt with occasionally when the submarine's reactor had been shut down for a considerable period.

Curiously, the natural reactors at Oklo were started by spontaneous fission.

Started, yes. I've already acknowledged that some source of neutrons is required to start the chain reaction and that neutrons from spontaneous fission are candidates for doing so.

But the starting of the Oklo reactor required something more than a ource of neutrons. Some action must have occurred such as adding a water moderator, or concentrating the uranium, or changing the shape of the "vessel" in which the uranium is contained. In other words by some change that actually affected keff so that it became > 1. The wikipedia article describes some possible scenarios.

Your argument regarding the natural state of enrichment does not rebut my argument in any way. Nor does the observation that natural reactors can no longer occur. As your source indicates, the reason that they can no longer occur is because of the ever decreasing amount of U235 relative to U238. That point is completely consistent with my argument as well as yours. But other factors suggest that I am correct.

It does not double the number of targets, but it does double the number of bullets, thus doubling the exposure of the targets, with the effect being the same as doubling the enrichment in material today. This would also be akin to providing a neutron reflector around the material.

I'll make two points regarding the above

First, increasing spontaneous fission is not akin to providing a reflector. A reflector allows some of those neutrons that escape the mass of uranium to have a second chance at creating fission. Increasing the number of source neutrons alone does not increase the chance that any one of those neutrons induces fission.

Further, simply increasing the generation rate of source neutrons won't decrease the percentage of neutrons that get absorbed in materials other than uranium, and would not necessarily decrease the percentage of neutrons that escape the mass of uranium.

Secondly, you are ignoring half of the argument that I made. Increasing enrichment increases both bullets and targets, while increasing the decay rate simply increases the bullets. I think it should be quite obvious that those two situations do not produce the same result. That should at least open up the possibility that increasing enrichment will increase keff (see six factor formula) while increasing the decay rate might not.

But let's address your questioning of whether I have considered what other reactions might increase if the decay rate is increased. I think this is a valid point.

The mechanism for increasing the decay rate has not been specified. At this point the mechanism is PFM (pure freaking magic). I think it is reasonable (but perhaps not inevitable) that the mechanism will increase spontaneous fission in the same way it increases U238 decay rates, exactly as you have proposed, and I have assumed that such a thing will happen.

But I don't think it is reasonable that the same PFM would inevitably change things such as the relative rates of absorption of neutrons in uranium vs. other materials, the rate at which neutrons are slowed down by a moderator such as water, or the probability that a neutron in the vicinity of a U235 atom actually gets absorbed. So absent a mechanism, I don't see how you can conclude that increasing the decay rate will inevitably produce a critical geometry.

I think our disagreement results from your belief that enrichment enables criticality by increasing the number of spontaneously generated neutrons. My position is that enrichment enables criticality primarily by increasing the number of targets available for each generated neutron.

Edited by NoNukes, : No reason given.


Under a government which imprisons any unjustly, the true place for a just man is also in prison. The proper place to-day, the only place which Massachusetts has provided for her freer and less desponding spirits, is in her prisons, to be put out and locked out of the State by her own act, as they have already put themselves out by their principles. Thoreau: Civil Disobedience (1846)

This message is a reply to:
 Message 60 by RAZD, posted 01-07-2012 9:13 PM RAZD has replied

Replies to this message:
 Message 64 by AdminModulous, posted 01-08-2012 4:09 AM NoNukes has seen this message
 Message 65 by RAZD, posted 01-08-2012 8:22 AM NoNukes has seen this message

  
AdminModulous
Administrator (Idle past 1374 days)
Posts: 897
Joined: 03-02-2006


Message 64 of 226 (647079)
01-08-2012 4:09 AM
Reply to: Message 63 by NoNukes
01-08-2012 1:00 AM


Radioactive Decay
Radioactive decay seems to be a classic textbook case of offtopic. Please, nobody continue spinning this thread into something it's not.

This message is a reply to:
 Message 63 by NoNukes, posted 01-08-2012 1:00 AM NoNukes has seen this message

  
RAZD
Member (Idle past 675 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 65 of 226 (647153)
01-08-2012 8:22 AM
Reply to: Message 63 by NoNukes
01-08-2012 1:00 AM


Decay rates, change, and atomic stability.
Per AdminModulous (Message 64)

I have initiated a new thread at Decay rates, change, and atomic stability, Message 1.

oops - preempted. See Message 3 of Spontaneous fission, decay rates, and critical mass

Enjoy.

Edited by Zen Deist, : revised link


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
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Portillo
Member (Idle past 3431 days)
Posts: 258
Joined: 11-14-2010


Message 66 of 226 (647736)
01-11-2012 3:57 AM
Reply to: Message 54 by Granny Magda
01-04-2012 9:17 AM


Re: Public vs Scientific Controversy
quote:
I can sympathise with you on that score, but the truth of the matter is that the debate amongst scientists has ended. All of the things we've touched on in this thread - evolution, common ancestry, human and animal migration, plate tectonics - they've been an accepted part of the scientific consensus for a long time now.

Why then do people prefer to chat here rather than on an evolution forum? Seems like there would be alot less stress in your life if you didnt have to deal with creation. Unless of course this place is a creationist rehabilitation center.

quote:
By the way, how do you feel about the model for marsupial evolution and migration that has been presented so far? Do you still have problems with it? If so, what is troubling you?

It seems like there is an agreement that the marsupials got to Australia from other countries.

Edited by Portillo, : No reason given.

Edited by Portillo, : No reason given.


And the conspiracy was strong, for the people increased continually - 2 Samuel 15:12

This message is a reply to:
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Replies to this message:
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 Message 68 by Larni, posted 01-11-2012 4:31 AM Portillo has taken no action
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caffeine
Member (Idle past 294 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 67 of 226 (647740)
01-11-2012 4:27 AM
Reply to: Message 66 by Portillo
01-11-2012 3:57 AM


Re: Public vs Scientific Controversy
It seems like there is an agreement that the marsupials got to Australia from other countries.

Well, that depends on what you mean. Kangaroos and wallabies, the topic of your original inquiry, didn't get to Australia from elsewhere. Kangaroos and wallabies have only ever lived in Australia and the surrounding islands (until humans began moving them about in the last few hundred years). This is what Granny was wondering if you had a problem with.


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Larni
Member
Posts: 4000
From: Liverpool
Joined: 09-16-2005


Message 68 of 226 (647742)
01-11-2012 4:31 AM
Reply to: Message 66 by Portillo
01-11-2012 3:57 AM


Re: Public vs Scientific Controversy
Why then do people prefer to chat here rather than on an evolution forum? Seems like there would be alot less stress in your life if you didnt have to deal with creation. Unless of course this place is a creationist rehabilitation center.

For some I guess it is. But what is there to debate on a pure evo site? Everyone is pretty much on the same page.

What I enjoy is reading the crazy things that some people write (often starting with 'I'm not a scientist but') and reading the replies (often from people with appropriate credentials) which are very informative (I've learnt SO much since coming here, all those years ago).

It seems like there is an agreement that the marsupials got to Australia from other countries.

Then how do you account for there being no native placental mammals in Australia?

Edited by Larni, : Punctuation


The above ontological example models the zero premise to BB theory. It does so by applying the relative uniformity assumption that the alleged zero event eventually ontologically progressed from the compressed alleged sub-microscopic chaos to bloom/expand into all of the present observable order, more than it models the Biblical record evidence for the existence of Jehovah, the maximal Biblical god designer.
-Attributed to Buzsaw Message 53

Moreover that view is a blatantly anti-relativistic one. I'm rather inclined to think that space being relative to time and time relative to location should make such a naive hankering to pin-point an ultimate origin of anything, an aspiration that is not even wrong.

Well, Larni, let's say I much better know what I don't want to say than how exactly say what I do.


This message is a reply to:
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Replies to this message:
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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 69 of 226 (647743)
01-11-2012 4:32 AM
Reply to: Message 66 by Portillo
01-11-2012 3:57 AM


Re: Public vs Scientific Controversy
Why then do people prefer to chat here rather than on an evolution forum? Seems like there would be alot less stress in your life if you didnt have to deal with creation. Unless of course this place is a creationist rehabilitation center.

You think creationists wouldn't turn up on an "evolution forum"?

It seems like there is an agreement that the marsupials got to Australia from other countries.

There is an agreement among scientists that the marsupials found in Australia today are indigenous to Australia and were never anywhere else.


This message is a reply to:
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caffeine
Member (Idle past 294 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 70 of 226 (647744)
01-11-2012 4:41 AM
Reply to: Message 68 by Larni
01-11-2012 4:31 AM


Australian placentals again
Then how do you account for there being no native placental mammals in Australia?

There are. Although Australia's placental mammal population seemed to be extinct by about 30 million years ago*, the continent was repopulated by bats and rodents over the last 15 million years.

*Which is something to consider next time someone trots out the tired old 'placentals are better than marsupials so drive marsupials to extinction when they coexist' line. Both coexisted in Australia, and there the marsupials won.


This message is a reply to:
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Replies to this message:
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Larni
Member
Posts: 4000
From: Liverpool
Joined: 09-16-2005


Message 71 of 226 (647748)
01-11-2012 5:44 AM
Reply to: Message 70 by caffeine
01-11-2012 4:41 AM


Re: Australian placentals again
That's interesting. I knew about bats but I did not know rodents were there, too. I thought they came over with people.

You live and learn, eh?

Edited by Larni, : Apelli k


The above ontological example models the zero premise to BB theory. It does so by applying the relative uniformity assumption that the alleged zero event eventually ontologically progressed from the compressed alleged sub-microscopic chaos to bloom/expand into all of the present observable order, more than it models the Biblical record evidence for the existence of Jehovah, the maximal Biblical god designer.
-Attributed to Buzsaw Message 53

Moreover that view is a blatantly anti-relativistic one. I'm rather inclined to think that space being relative to time and time relative to location should make such a naive hankering to pin-point an ultimate origin of anything, an aspiration that is not even wrong.

Well, Larni, let's say I much better know what I don't want to say than how exactly say what I do.


This message is a reply to:
 Message 70 by caffeine, posted 01-11-2012 4:41 AM caffeine has taken no action

  
Granny Magda
Member (Idle past 105 days)
Posts: 2384
From: UK
Joined: 11-12-2007


(2)
Message 72 of 226 (647776)
01-11-2012 9:08 AM
Reply to: Message 66 by Portillo
01-11-2012 3:57 AM


Re: Public vs Scientific Controversy
Hi Portillo,

Why then do people prefer to chat here rather than on an evolution forum? Seems like there would be alot less stress in your life if you didnt have to deal with creation.

Perhaps, but also a lot less fun.

What draws most of us here is a love of adversarial debates. That naturally requires that two parties take differing views. Without anyone to have a good old knock down argument with I'd be bored!

There is also the fact that however settled the issue of evolution might be amongst scientists, there is still a controversy amongst the public. Clearly more has to be done to win that argument. I get annoyed when I see creationists trying to persuade schools to teach wrong-headed nonsense. I get annoyed when I see scientists coming under attack just for doing their jobs. I get annoyed when I see religion trying to insinuate itself into the scientific arena. For all these reasons I feel that it's necessary to oppose creationism.

Unless of course this place is a creationist rehabilitation center.

I think that there's an element of that for many of us. You have to realise that from our perspective, creationism is a false teaching. And who are the main victims of this falsehood? Creationists themselves, who have been duped into putting a lot of effort and importance into nonsense. I think that it's unfair to the ordinary creationists. You deserve better than to be lied to by the religious leaders who you trusted. Someone has to tell you guys the truth sooner or later. Sorry if this sounds patronising, but there it is.

It seems like there is an agreement that the marsupials got to Australia from other countries.

Not really. I am proposing that marsupials reached Australia by migrating across continents that have long since fragmented. You seem to think that they were dropped off in a boat or something. I still think that we're very far apart.

Can I ask you what exactly you find unconvincing about the scenario I've outlined?

Mutate and Survive


This message is a reply to:
 Message 66 by Portillo, posted 01-11-2012 3:57 AM Portillo has replied

Replies to this message:
 Message 73 by Percy, posted 01-11-2012 9:21 AM Granny Magda has replied
 Message 77 by Portillo, posted 01-13-2012 3:58 AM Granny Magda has replied

  
Percy
Member
Posts: 20829
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.6


Message 73 of 226 (647778)
01-11-2012 9:21 AM
Reply to: Message 72 by Granny Magda
01-11-2012 9:08 AM


Re: Public vs Scientific Controversy
Granny Magda writes:

Not really. I am proposing that marsupials reached Australia by migrating across continents that have long since fragmented. You seem to think that they were dropped off in a boat or something. I still think that we're very far apart.

I've been assuming the Australian marsupials have always been native to Australia. Wither Australia went, so went they.

--Percy


This message is a reply to:
 Message 72 by Granny Magda, posted 01-11-2012 9:08 AM Granny Magda has replied

Replies to this message:
 Message 74 by Granny Magda, posted 01-11-2012 9:52 AM Percy has replied
 Message 76 by caffeine, posted 01-11-2012 10:17 AM Percy has seen this message

  
Granny Magda
Member (Idle past 105 days)
Posts: 2384
From: UK
Joined: 11-12-2007


Message 74 of 226 (647781)
01-11-2012 9:52 AM
Reply to: Message 73 by Percy
01-11-2012 9:21 AM


Re: Public vs Scientific Controversy
Hi Percy,,

The modern Australian marsupials are all native to Australia, yes. I was talking about the original marsupials, as I outlined in Message 31. The first known marsupials lived in what is now China.

Mutate and Survive


This message is a reply to:
 Message 73 by Percy, posted 01-11-2012 9:21 AM Percy has replied

Replies to this message:
 Message 75 by Percy, posted 01-11-2012 10:16 AM Granny Magda has seen this message

  
Percy
Member
Posts: 20829
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.6


Message 75 of 226 (647787)
01-11-2012 10:16 AM
Reply to: Message 74 by Granny Magda
01-11-2012 9:52 AM


Re: Public vs Scientific Controversy
Hi Granny!

China! I didn't know that. Went to Wikipedia, it says my assumption was wrong. I assumed marsupials were already on the Australian continent when it split off, but the Wikipedia article on marsupials says they migrated through Antarctica to reach Australia after it had already split off, possibly rafting across what was then a narrow gap.

Tying this in to the topic, the fossil evidence for this migration is about 50 million years old, as is the geological evidence placing Antarctica and Australia in close proximity. Evidence for a migration from the Middle East to Australia around 5000 years hasn't been discovered yet. Neither have we found any historical drawing or rendering or mention of creatures as unusual as kangaroos.

--Percy


This message is a reply to:
 Message 74 by Granny Magda, posted 01-11-2012 9:52 AM Granny Magda has seen this message

  
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