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PostPosted: Thu Jul 03, 2008 8:51 am 
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What I'm saying, Joe, is that I don't experience "Time" as a discreet property. All I experience is the movement of things and this is the only phenomenon I can be certain of.
To be fair, I find it impossible to get my head round such concepts as relativity theory and quantum mechanics.
I recall Bertrand Russell in a T.V. or radio interview many years ago saying that, people who are only acquainted with Euclidean geometry, will not be able to understand Relativity.

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PostPosted: Thu Jul 03, 2008 11:31 am 
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Well, I agree, time is certainly something that is very difficult to pin down. I often think it is described as a discreet property, as you put it, in the wrong context. I'm not sure if that's the case here in this thread/subject because one minute it's "time", then it's "the future" and "the past". :?

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PostPosted: Fri Jul 04, 2008 10:23 am 
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As I understand it, when physicists refer to "time", "curved space" and "multi-dimensions", etc, they mean them as mental concepts for modelling purposes, whereas the lay-person is apt to think of these things as actually existing.
I remember seeing an Open University programme on TV showing the famous slit experiment with light. The physicist doing the demonstration said that, on the basis of the experiment, light can be regard as either particles or waves. He did add, however, that light is neither particles nor waves, only that it behaves as such in given experiments.

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PostPosted: Fri Jul 04, 2008 11:05 am 
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Hi all,
Time is the most difficult of subjects to understand. We have our clocks based on the frequecies in our own solar system which we use to our advantage. That is not the same as spacetime however, spacetime is a Universal entity which governs the future of all matter in that Universe.
Einstein comments that all matter moves 'forward' in spacetime. Forward is not a 3D direction which you can see. The way I see it is that matter 'punches' its way into a dimension that is not possible for the human mind to comprehend - the future. Ruud suggests that as matter 'punches' it's way into the future, light because it has no rest mass has no 'punch' and is left behind. This makes spacetime everywhere in every direction or every possibility. Time will tell if Ruud has a valid point but I've thought about and I just like the idea. I can also see where it fits into Einstein's idea too.


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PostPosted: Fri Jul 04, 2008 12:34 pm 
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:shock: :shock: :shock:

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PostPosted: Fri Jul 04, 2008 8:41 pm 
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brian livesey wrote:
As I understand it, when physicists refer to "time", "curved space" and "multi-dimensions", etc, they mean them as mental concepts for modelling purposes, whereas the lay-person is apt to think of these things as actually existing.


They do exist, Brian. We're just not set up to perceive them with our senses, so we have to use our ordinary language to describe the extraordinary.

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PostPosted: Fri Jul 04, 2008 9:21 pm 
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Dear al(L)
I think with respect to time everyone has said something that is valid but in the context of their\our own way of thinking.
I personally do not think time is just a human concept but the way we actually tend to measure time is usually a human concept.
I think I have read that there was a time when the 24 hour day was 12 hours daylight 12 night. The result being that in summertime the 12 hour daylight period was actually a lot longer than the 12 hour winter daylight period. Whilst when the railways were built time was a problem because clocks were set differently in different parts of the country, in particular places to the east and others to the west.
RLastro mentions a different possible problem ie with respect to humans living on different planets with very different orbital periods.
Joe mentions another problem, although I am not completely sure I understand the idea that time would not work if light travelled at infinite speed. I suppose I may have always tended to take time for granted, and light speed and gravity. I suppose the Universe might be very different if light and gravity travelled infinitely fast (ie instantly) ?
Best of luck from Cliff


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PostPosted: Sat Jul 05, 2008 12:21 pm 
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I don't see how Paul can claim that things unperceived by our senses exist.
We can't know this until through taste, touch, vision or sound, or a combination of these senses, we perceive them.
It might be argued that the instrumentation we use can detect phenomena independently of our senses, but, we can't know what the instrumentation is telling us except through our sense perceptions of the instruments themselves.
It would help if scientists would take the trouble with the lay-public to differentiate between what are scientific mental models, needed for prediction and control, and reality itself. It's easy for the uninitiated to confound the two.

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PostPosted: Sat Jul 05, 2008 12:53 pm 
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brian livesey wrote:
It might be argued that the instrumentation we use can detect phenomena independently of our senses, but, we can't know what the instrumentation is telling us except through our sense perceptions of the instruments themselves.
It would help if scientists would take the trouble with the lay-public to differentiate between what are scientific mental models, needed for prediction and control, and reality itself. It's easy for the uninitiated to confound the two.


Our inferences on the nature of time, gravity etc are via instrumentation that our senses perceive. Where do you draw the line, Brian?

We can't see UV light, but bees can and we have developed instruments to show it exists. Without my specs on or contacts in, I can't see much beyond 10 or 20 metres.

Theories of light, gravitational waves etc are very clearly and easily devolved from instrumentation that we have developed over the last 100 years or so. This knowledge is obviously a little more complex than me putting my specs on to see the moon or using a UV camera to capture light at wavelengths I can't naturally perceive.

You don't need much knowledge to understand what you perceive directly but you need a lot more if you head into areas that use a lot of scientific instrumentation. That goes for cosmology as much as it does for neurology or any other science you care to mention.

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PostPosted: Sat Jul 05, 2008 1:00 pm 
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What you say, Paul, doesn't contradict what I've said about our senses. Without our sense perceptions we wouldn't know that bees dectect U.V. in the first place because we would have no way of knowing that bees and U.V. exist.

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PostPosted: Sun Jul 06, 2008 11:08 am 
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Dear Brian
I think I see what you are getting at, but I am not sure we are in agreement.
For example, suppose someone is born in the dead of night, when the Sun is invisible. Does that mean that the Sun does not exist at all (at least for them) until after sun-rise next morning.
I think I have read several versions of the idea that things do not exist until they have been observed, but surely it is really just another "mind model" that might have its uses but like so many models is far from perfect.
Best wishes from Cliff


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PostPosted: Mon Jul 07, 2008 9:16 am 
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The Sun would still exist for the community, if apparently not for the baby, because the Sun's existence is already known about.

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PostPosted: Mon Jul 07, 2008 10:00 am 
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This relates to the 'Strong Anthropic Principle', one variant of which states that "Observers are necessary to bring the Universe into being." (Barrow and Tipler)
I have great difficulty in accepting that all the distant galaxies that were detected by the Hubble 'scope were not there before they were detected...


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PostPosted: Mon Jul 07, 2008 5:05 pm 
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brian livesey wrote:
What you say, Paul, doesn't contradict what I've said about our senses. Without our sense perceptions we wouldn't know that bees dectect U.V. in the first place because we would have no way of knowing that bees and U.V. exist.


Following from George's observation; if we were suddenly blown to smithereens, Brian, UV and everything else in the universe would continue to exist. I would argue that no humans or any sentient being need to perceive anything in order for anything to exist.

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PostPosted: Mon Jul 07, 2008 6:12 pm 
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We've been here before, of course. BTW, I may be wrong but I don't think that Brian is saying we need to be around for things to exist.

Anyway, one hundred years ago I might have agreed with Brian but things aren't so black and white these days. Mathematical models and computer simulations are very powerful tools. They are capable of adding to what we know. We are no longer limited by our five senses when dealing with phenomena that cannot be sensed directly. There also seems to be a bit of an overlap or confusion between what we sense and what we know - "time" being a good example.

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