If I understand now, you're simply inverting the need for proof in regard to Astrology. This is pretty simple, as such negative criteria are both common in epistemology and belief. Instead of your example of God, allow me to suggest aether. This was taken to be a fifth element which filled all otherwise empty space, or both substance and medium. Science in the nineteenth century science suggested aether was superfluous, and the understanding of science itself changed so things which could not be measured became unscientific.

However anyone could invert this and claim things which are measurable are the unscientific ones! Say one was to take provability rather than falsifiablity as the scientific principle. Science would be a tool for proving things rather than disproving them. If claims worked in this direction multiple proofs would occur, mutually exclusive ones making any measurement suspicious...

Suffice to say, it sounds like the use of science rather than the tool of science is your issue, and it's not a bad one to share. Any one taking current scientific belief as their criteria would believe the Milky Way has irregular arms, and twenty years ago that it had four. Twenty years prior to this they would believe it had two arms. And fifty years prior to this it would have been a universal cloud of stars.

And all I can say in my defence is that it was on the best evidence at the time...!

I`ll have to do some research on the falsifiabilty factor you mention; I don`t understand the term in the way you use it.
  You`re getting closer to my view of science, but if I may explain it another way.
Imagine a young child painting a picture. To the childs eyes and the eyes of other children the picture is accurate.
To the sophisticated eyes of an adult this is not so. The colours would be too basic and there would be no perspective or composition etc,etc,....
But it would be wrong to prevent that child from painting simply because he/she has yet to develop the necessary skills of co-ordination and observation, etc that is required. This is my view of science; that it is still learning and should continually learn. And when science makes mistakes (as it inevitably will continue to do from time to time) then it should learn from those mistakes. To do otherwise would be to ditch science in favour of,...What? Magic?
My gripe is not with science but with appointed or self appointed experts, not just in the field of science but wherever they may be found, who attempt to tell others what to think, believe or accept. They tend to have a biased view.

http://en.wikipedia.org/wiki/Falsifiability

As a very silly example, "Brontosaurus were thin at one end, much much thicker in the middle and thin again at the other end." is a falsifiable (and scientific) statement. Or Apatosaurus if you prefer.

I think that slowly, ever so slowly I am getting there. But first, three thoughts of mine.
1) I can see why epistemolgy interests you so.
2) I think I`m beginning to understand why the majority of your replies tend to be terse and succinct.
3) It`s fortunate that we are not neighbours because I think I would have smashed every window in your house by now. The whole notion of falsifiability is driving me mad and yet I can`t leave it alone. And that is just ONE(?) aspect of the subject ??

As best as I am so far able to interpret, I take it that falsifiability is something of a combination of Trial by Fire and the old adage "the exception proves the rule" albeit in the theoretical stage.
Before you correct me, yes I know this is a simplification (if it is indeed approaching accuracy) but my mind is still running ten to the dozen to make complete sense of it.
It doesn`t help that,in my search,I have read refutations of the concept which coincide with my own pre-conceptions; a factor recognised by Popper, or so I believe. Could a fair falsifiable statement read thus,...
"I built a brick wall that can`t be knocked over even with a truck. I know this because the truck was crushed in the attempt.
However, if I took away the mortar I could knock it over with one hand. Not all brick walls are built with mortar"?

This is far too complex. Falsifiability means a proposition can be proved false.
I'll have to unpack your statement--

terry : "I built a brick wall that can`t be knocked over even with a truck. I know this because the truck was crushed in the attempt. However, if I took away the mortar I could knock it over with one hand. Not all brick walls are built with mortar"?

OK, brick wall that can't be knocked over with a truck. This is falsifiable; we could do the experiment and see. Or we could take it that this relates to one truck only.
It's better to treat the second half as another proposition--If I took away the mortar...yes, that's falsifiable. Although very messy! The final sentence doesn't add to this; we could treat it as a third and falsifiable proposition!

Sorry; just as I think I am getting there I find that it all falls apart for me. Can I ask,..?
  "The moon orbits the Earth."
That,to me,seems to be a simple scientific statement of fact.
Now, where is the falsifiability factor in an established fact like that?

That's a good one; yes it's falsifiable.
Our observations can disprove it.
We could say the moon and Earth are static and the rest of the universe spins around them. This'd be falsifiable 'cos the moon/Earth system isn't static, the distance changes between the two.
Or that the Earth orbits the moon. If you wanted to use the moon as the reference point, all the orbital changes indicate they're caused by outside influences.
Back to the moon orbiting the Earth. The current view is that they orbit each other, with a common center of gravity with the Earth's sphere. Which in turn is falsifiable as better observations could show the common center of gravity is outside the Earth's sphere, or is the same as the Earth's center--proving the moon does orbit the Earth!

I would have thought there was a mathematical formula to determine the locus? or common centre.
This falsifiablity is either more complex or more simple than I realise.
I see it as a challenge to a hypothesis to ensure the greatest degree of accuracy possible, the viewing of another possible aspect from the simplest or most obvious conclusion. However, it seems not to be quite so simple.
As for my own view of science which you asked earlier, I heard it stated more concisely on TV the other day; science is a self correcting system (or at least it should be.)
    Anyhow, it would be nice to know whether I am getting closer to the mark or wandering blindly further astray.
In the meantime, it`s back to Popper for me.

Probably simpler if it's still confusing.
Yes; a formula for determining the common center of gravity would be simple; however it's still observation driven. If something unexpected suddenly caused scientists to decide the universe spun around the moon...! They launched the most sophisticated gravity probe yet in 2004, which could turn up surprises, albeit probably not that one!

Perhaps you can think of is in terms of maths (which is not falisifiable and hence not a science). All sums are not "1 + 1 = 2" but less definitively "if 1 + 1 => 1 or =< 3". Subsequent variants on the equation may get closer to the value of 2, but any such claim can always be overturned by a more accurate experiment/evidence/theory.

Thanks. I actually think i`ve got it. I had this Eureka moment after my last reply whilst reading Popper again. I did reply but there is a time-out factor on the site so, after I had spent about twenty minutes waffling on the message was wiped without being sent. I was too tired to type it all again.
Anyway, simply put; falsifiability determines the strength of a theory.
The more factors that Might be disproved in a theory can add to its strength. The more get out clauses (ands/ifs/buts) or conventional twists attached to a theory, the weaker it becomes.
I think I had trouble with this on two points. First, I associated falsifiability with infallibility, though I don`t know why.
Second, it seemed to be saying that if you DO prove something wrong then it must be right. Seems to be a question of semantics!
Thanks for your help. I`m sure that is just the tip of the iceberg but it`s all I can handle for now. I`m going to look deeper into the whole subject of epistemology, it really does appear to be interesting.

I get that too! I've found copying the text prior to the sending is vital--perhaps we need to increase the log on time?

This is true; the more falsifiable the theory is the stronger. A weak theory (and this goes for arguments) is that much harder to disprove by virtue of the fact that it makes mundane claims.

Good luck with epistemology; perhaps it's just me but truth is the single greatest thing to debate. I say Plato got it wrong in placing beauty at the top of the hierarchy of Forms. Truth may be ugly, but it defines what's real and what isn't.

As a bit of an exercise I jotted down things of interest to me (not comprehensive or ordered):

Philosophy of science
Epistemology
Philosophy of history (esp. analytic)
Korean war
Relativism
Archaic theories (esp. scientific)
Challenges to science/reason
Joseph R McCarthy
Doctor Who
Preservation
Classification
Historiography
Space race (esp. 1965-1966)
Planetary science (esp. geology)
Structure of the universe
Metaphysics (esp. free will vs. determinism)
Analog vs. digital
Carter vs. Reagan

...you can see how many of these we've checked in this thread!

It seems pretty much comprehensive to me.
I tried the same exercise and struggled to get five. Two questions: What about Clarke, Asimov or Dick ?
And how does Dr Who fit into such a heavyweight list of interests? Is it of some significance or a question of light relief; an escape from the more serious subjects?

In reverse order, I think the body of work that is Who is as deep or shallow as the viewer bothers to make it...if you want to engage all the works behind it or just treat it as eye candy it's all good.

I cut my literary teeth on Asimov and Clark (the order of books I first read goes The Martian Way, The Sands of Mars and Islands in the Sky), although I was soon supplementing them with Heinlein and a series of anthologies edited by Damon Knight called Orbit. One of the most painful discoveries as an adult was finding that the State Library of South Australia (which was a lending library at the time) and the Adelaide Lending Library have weeded their collection of these hardcovers. Mind you in the '80s ALL had the latest Who novelizations in hardcover every month, sadly gone too...

Another favourite was Walter Hughes, who wrote a juvenile series about exploring the solar system from Woomerra. Despite being set here in South Australia the novels are rare locally; a survey I conducted five years ago found the most complete collection at the National Library of Canada!

Dick I still have an incomplete knowledge of; for years the only novel I had of his was a rare collaboration called The Ganymede Takeover. However he's a short story author without measure. Expect to see more Hollywood adaptions as they realize they're bankrupt of plot bunnies, and that Dick alone could supply the movie industry with plots for the next century.

Having said all this, it must seem pretty apparent that I'm into hard SF. McCaffrey, Le Guinn, Pratchett and Piers Anthony leave me cold. I really don't think much of the fantasy invasion from the '60s on, fortunately it's not as if the genre's entirely stuffed!

Coming back to your question, the last Asimov I read was his dying autobiography I, Asimov and the last Clark was the co-authored Rama novels. My opinion of Asimov has gone down as I read more of his detective stories and saw how little effort he used to make them cross over to SF; Clark has gone up as I appreciate how he improved as a writer and learned how to write about human beings in the '70s.

I agree with regards to Asimov and Clarke, however I think you missed some of the real greats including:
Harry Harrison (does anyone remember soylent green?)
"Doc" Smith (lensman - can you say  cheezy space-opera)
Douglas Adams (Mainly H2G2, but Dirk Gently is good too)
Gillian Rubinstein (local talent, mainly teen and younger audience)
Robert Silverberg (Sundance was awe inspiring when I read it in grade 6)
Larry Niven (Ringworld)

These are just a few I read (and re-read) When I get home, I might add a few more to this list, or maybe just put up a list of my entire Sci-Fi collection

So much to discuss here.
Doc Smith, A E Van Vogt, Heinlein, Nation and an army of other authors deserve mention. But this is a thread of its own.
Talking of threads, this one seems to have meandered away from its original subject.
Sorry !
  Anyone out there still interested in the original question about time travel ?
By the way, saw episode 3 tonight.
    No comment!

Why is it that time travel has such a varied law. you think after two hundred years of storie righting there would be a standard practise. It is just like Vampires which change from writer to writer.

With time travel stories anything can happen! Best of all,as far as the writer is concerned, any mistake in the plot can either be explained away as a vagary of time or the solution can be `put on hold` until a satisfactory conclusion is established. Better even than this; it can remain unexplained until the sequel or even prequel is subsequently published, if ever,..

The single best treatment I've ever seen of time travel was a 1996 episode of The Outer Limits called A Stitch in Time. Suffice to say it makes a case for consistent application of cause and effect!

It has a sequel of sorts in Final Appeal.