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Offline tamurello

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Expanding Universe
« on: 11/05/2005 11:13:40 »
I have a question for the astronomical experts out there.  We live in an expanding universe - has this expansion ever been extrapolated to a distinct centre where it started?  If so has anyone tried to look there with a telescope to see the 'Big Bang'?  Also, the expansion is actually accelerating isn't it?  Could it be the case that wherever you stand in the universe it is expanding away from you?


 

Offline gsmollin

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Re: Expanding Universe
« Reply #1 on: 11/05/2005 11:57:56 »
Cosmologists tell us that there is no spatial center to the universe, because the big bang was an expansion of space itself. Everywhere one looks, it is the same. This makes little sense on a human-length-scale, but that is the explanation.

There are other, parallel reasons. The universe is apparently very big, much much larger than the 14 billion light years we can see of the observable universe. All of it we can see is just the light reaching us for the last 14 billion years, the age of the universe. Beyond that is lots more universe, just like this part, but too far away for us to see. Its like trying to determine where you are on a dark foggy London road, when you can't even see as far as the curb.

The expansion has been verified many times. Its rate has been measured and remeasured many times with always differing results. The latest set of measurements, of the rate of change of the rate of expansion shows a small increase. I cannot confirm or endorse this result, since it is preliminary. Perhaps we will learn more about this in the future.
 

Offline DoctorBeaver

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Re: Expanding Universe
« Reply #2 on: 11/05/2005 17:21:52 »
If there is a lot of the universe than we can see, how can it be said that it's however-old? If we don't know how big it is, how can we tell how long it's been expanding?
 

Offline Deanwinfield

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Re: Expanding Universe
« Reply #3 on: 12/05/2005 20:11:24 »
quote:
how can we tell how long it's been expanding?


Red shift shows that doesn't it?

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Offline gsmollin

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Re: Expanding Universe
« Reply #4 on: 13/05/2005 13:32:24 »
quote:
Originally posted by DoctorBeaver

If there is a lot of the universe than we can see, how can it be said that it's however-old? If we don't know how big it is, how can we tell how long it's been expanding?



The cosmic background radiation (CBR) is the red-shifted remnant of the primordial fireball. When the universe was about 300,000 years old, the firball cooled enough to allow ionized protons to combine with electrons to form molecular hydrogen. At this time the universe became transparent to radiation, and the trapped photons escaped. Now we see a microwave radiation corresponding to black body radiation at 2.7 K. Scientists can work out the red-shift very accurately, because the temperature of recombining hydrogen can be determined in a laboratory. The red-shifting between these two numbers tells us how far away the CBR appears to be, using the Hubble constant of universal expansion. From that we know how long it has been traveling to reach us. Other big-bang theory gives us the 300,000 year age of the universe at hydrogen combination.
 

Offline gsmollin

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Re: Expanding Universe
« Reply #5 on: 13/05/2005 13:37:02 »
quote:
Originally posted by Ruzz5000

is time dependant on the expanding universe? if so what would happen if it started to contract? would time go backwards? and would we remeber what we had done before time went backwards?

Russ



That one has been speculated many times. If the universe were closed, and went through a contraction phase, some scientists did postulate the arrow of time would reverse. Frankly, I never believed it would. I don't think cause and effect can be interchanged. Anyway, there is no longer any evidence there will ever be a contraction phase. The universe is either flat or open, and the arrow of time will continue to point into the past.
 

Offline qazibasit

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Re: Expanding Universe
« Reply #6 on: 13/05/2005 18:31:55 »
well the deflection of the spectrum of different stars towards red is showing us that the universe is expanding and even the Friedmanns models are spporting this concept but what is disturbing me is that which force is inflencing them to move away coz there is nothing to support this idea that they are moving since the big bang or this might be possible that there is any galaxy in this universe which is comming closer to the milky way having different elements the anti particles which we have in or universe and due to its electromagnetic field which is a million million times more powerful than the gravity is attracting the stars of or galaxy and once they collide everything will get vanished.
 

Offline DoctorBeaver

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Re: Expanding Universe
« Reply #7 on: 15/05/2005 13:48:01 »
Thanks, gsmolin - I understand now.

Also, doesn't 1 of the laws of thermodynamics prevent the reversal of the arrow of time - In a closed system the level of entropy can never decrease? (or words to that effect)
 

Offline gsmollin

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Re: Expanding Universe
« Reply #8 on: 16/05/2005 13:57:32 »
Right, that's the second law of thermodynamics. That law was the problem with contracting phases to the universe. If the universe were closed, and went through cycles of expansion and contraction, then it follows that the contractions would need to reverse the second law at some point. Clearly this is the case, since we are increasing entropy now, and if the universe has been at this stage of an infinite cycle an infinite number of times before, then entropy would already be infinite and unable to increase any more.

It is not clear when the entropy would decrease in a contracting phase. It might occur all at once inside the "singularity point" at the beginning of a new expansion phase. Inside that singularity it might be possible to break the second law; it is a singularity. However, I never found that satisfying, and I am happier with the flat universe that expands forever. It seems like the simplest explanation. Things happen once, then they are over forever.

I also think that is a pertinent message for us all, since things can only happen once, we should all live our lives with attention to the moment and stop grousing about the past. It is gone.
 

Offline DoctorBeaver

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Re: Expanding Universe
« Reply #9 on: 16/05/2005 22:27:17 »
But, surely, if Time began with the Big Bang then however many Big Bangs there are (if the expand/contract theories are correct) Time will begin again with each expansion. Therefore, wouldn't any laws that existed in a previous cycle revert to null & start again? How could the 2nd law of thermodynamics continue to hold true if time itself had ceased to exist? That would lead to the conclusion that any entropy that existed in a previous cycle would be negated so any subsequent expansion would not contravene that law


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Offline neilep

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Re: Expanding Universe
« Reply #10 on: 16/05/2005 23:00:23 »
Thank you once again for a fascinating thread chaps (and chapess's ?)

Can I ask if Time has a speed limit ?...I think I meant to ask ' how is the speed of time determined ? '

What is it that makes us perceive time at the rate that we do ?.......I'm not making any sense am I ?...it's soooo frustrating when you can't find the words to elaborate efficiently......going to bed, taking some sleep tabs and seeking Z's....

thanks again for the great thread though.......



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Offline chimera

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Re: Expanding Universe
« Reply #11 on: 16/05/2005 23:24:36 »
quote:
Originally posted by neilep

I think I meant to ask ' how is the speed of time determined ? '

What is it that makes us perceive time at the rate that we do ?.......I'm not making any sense am I ?



Perfectly valid question Neil, time is as far as I know not directly measurable, except through something changing visibly, and measure that rate of change against a preset clock, which is set to another such clock etc. until you run out of clocks.

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Offline DoctorBeaver

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Re: Expanding Universe
« Reply #12 on: 17/05/2005 12:11:47 »
Clocks don't measure time, they merely help us chop it up into manageable segments.
Einstein showed that time isn't a constant but depends on the frame of reference of the observer. Surely, trying to measure something that changes depending on how you observe it makes the task impossible as the measurements from within 1 frame of reference would be at variance with those from another.

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Offline neilep

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Re: Expanding Universe
« Reply #13 on: 17/05/2005 12:33:13 »
Thank you Rob and Eth.

Though I understand that the passage of time is relative to from whence it's observed, but when you're at a location is time moving at a constant rate at that place ?...I suppose I should have stipulated that in my question above that I meant in particular to your own geographical location does time move at the same speed ?...in other words, at any point where you are, from your own perspective, is time moving at the same rate ?.......I think I've just confused myself further because I presume we wouldn't realise it(from our personal perspective) if we suddenly moved into a point in space where time moved forward at a different rate. I'm thinking that maybe there's a place, where if we entered it, we'd age a lot quicker or slower maybe ?

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Offline DoctorBeaver

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Re: Expanding Universe
« Reply #14 on: 17/05/2005 13:54:30 »
Neil, I don't believe so. As some1 which a much greater intellect than I have once said "Put your hand in a bucket of frozen water for a minute & it seems like an hour. Be in the company of a charming lady for an hour & it seems like a minute. That's relativity!"
I may not have got the quote exactly, but the meaning is still there.
I suppose that raises another question - if observing an object alters its state (Heisenberg) then can our perception of time alter that also? Would that explain why some days drag & others seem to fly past. And why is it that as one gets older time seems to pass quicker? Surely, if time were a constant then every year, day, hour, second etc would seem just as long as any other.
The lifespan of a mayfly is only 1 day. But to a mayfly does that 1 day seem as long as 70 or 80 years does to us?
Ahhh, I've just thought. I can use this as an excuse for being late. I can say that time in my frame of reference was running slower so it took me longer to get there!

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Offline neilep

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Re: Expanding Universe
« Reply #15 on: 17/05/2005 14:13:07 »
ETH, funny you should mention the Mayfly...I was literally just about to add it to my comment above....thanks for your answer. very interesting that the act of purely observing something could alter it.... and regarding being late, take the rest of the week off !!..tell them I said it's ok, there's plenty of time !!...cheers

Neil:)

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Offline DoctorBeaver

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Re: Expanding Universe
« Reply #16 on: 17/05/2005 14:54:52 »
Thanks, but I'm off work this week anyway

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Offline gsmollin

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Re: Expanding Universe
« Reply #17 on: 17/05/2005 18:10:51 »
So, when you're off of work, does a day seem like an hour, or do you get nagged and an hour seems like a day? You don't have to answer that.

We measure that most peculiar dimension, time, by using the speed of light. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. That radiation travels at c, so time is measured by radiation moving at c. Indeed, in special relativity, the 4 space-time dimensions are x, y, z, and -ict. Time is the dimension moving at c. That's why it is so different, and we seem to be "stuck" in time, unable to move through it.
 

Offline gsmollin

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Re: Expanding Universe
« Reply #18 on: 17/05/2005 18:16:13 »
quote:
Originally posted by DoctorBeaver

But, surely, if Time began with the Big Bang then however many Big Bangs there are (if the expand/contract theories are correct) Time will begin again with each expansion. Therefore, wouldn't any laws that existed in a previous cycle revert to null & start again? How could the 2nd law of thermodynamics continue to hold true if time itself had ceased to exist? That would lead to the conclusion that any entropy that existed in a previous cycle would be negated so any subsequent expansion would not contravene that law


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That's what I said. That's the un-satisfying answer. We can break the second law at the singularity point corresponding to the beginning of the big bang. I am reminded of a short story by Isaac Asimov, "The Final Question". The final question was "Can entropy ever be reversed?" The stock answer, throughout time, was "Insufficient data for meaningful answer." I like to quote that from time to time. It was a good story, check it out.
« Last Edit: 17/05/2005 18:16:52 by gsmollin »
 

Offline qazibasit

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Re: Expanding Universe
« Reply #19 on: 17/05/2005 18:54:26 »
well its to difficult to say about such aspects coz they are just our predictions and it takes millions of years for the thing to occur.
 

Offline neilep

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Re: Expanding Universe
« Reply #20 on: 17/05/2005 19:02:39 »
quote:
Originally posted by gsmollin

So, when you're off of work, does a day seem like an hour, or do you get nagged and an hour seems like a day? You don't have to answer that.

We measure that most peculiar dimension, time, by using the speed of light. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. That radiation travels at c, so time is measured by radiation moving at c. Indeed, in special relativity, the 4 space-time dimensions are x, y, z, and -ict. Time is the dimension moving at c. That's why it is so different, and we seem to be "stuck" in time, unable to move through it.



Gsmollin, you have this knack for taking the words out of my mouth :)...if Time is a thing , could it also be a tangible thing ?.if it is, does that mean one day we can control it ?

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Offline DoctorBeaver

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Re: Expanding Universe
« Reply #21 on: 17/05/2005 19:54:52 »
I am in the fortunate position of not having anyone to nag me apart from my 11 dogs

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Offline DoctorBeaver

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Re: Expanding Universe
« Reply #22 on: 17/05/2005 19:59:26 »
quote:
Originally posted by gsmollin

We measure that most peculiar dimension, time, by using the speed of light. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. That radiation travels at c, so time is measured by radiation moving at c. Indeed, in special relativity, the 4 space-time dimensions are x, y, z, and -ict. Time is the dimension moving at c. That's why it is so different, and we seem to be "stuck" in time, unable to move through it.



Surely, though, if caesium were travelling at near C the decay would appear to have a different rate depending on where you were observing it from. Doesn't that preclude there being an absolute value for time?

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Offline chimera

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Re: Expanding Universe
« Reply #23 on: 17/05/2005 20:42:17 »
quote:
Originally posted by gsmollin

So, when you're off of work, does a day seem like an hour, or do you get nagged and an hour seems like a day? You don't have to answer that.

We measure that most peculiar dimension, time, by using the speed of light. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. That radiation travels at c, so time is measured by radiation moving at c. Indeed, in special relativity, the 4 space-time dimensions are x, y, z, and -ict. Time is the dimension moving at c. That's why it is so different, and we seem to be "stuck" in time, unable to move through it.



The fact that time 'feels' longer or shorter has no basis in physics, of course, but is entirely subjective... [:I]

Equally subjective is it to come up with an arbitrary means of measuring it. It does not say ANYTHING about time, but how many cycles are counted in a certain prespecified equally arbitrary second.

It's called tautological or circular thinking. Cesium-133 and its number of cycles per 1/36000th of the daily rotation of this backwater planet say nothing about time itself, only about each other. This can come in very handy, but nothing more.

Time is perceived action by an object, and our memory the only assurance it was once not so. How you slice it after that, is again, completely arbitrary.

More important question philosopically is that if time is a real (absolute) thing, it would mean that the whole of reality would work like a large PC screen, with a common 'refresh rate', or uniform 'redrawing of reality' shared by each different location in this universe.

So far, that does not appear to be the case. Time appears as a very localised, chaotic phenomenon, not shared by any other location, i.e. that all clocks can essentially have their own unique 'now'.

The living are the dead on holiday.  -- Maurice de Maeterlinck (1862-1949)
« Last Edit: 17/05/2005 20:45:35 by chimera »
 

Offline DoctorBeaver

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Re: Expanding Universe
« Reply #24 on: 18/05/2005 12:49:01 »
OK, so what if the refresh rate of the screen were dependent on the output from a capacitor? The amount of current flowing into the capacitor would determine its discharge rate. So, if the current were reduced, the disharge rate would decrease as would the refresh rate. But, if that refresh rate were time itself & determined our perception of it, then surely by slowing it down our perception of it would also be slowed and it would appear to us that it were always refreshing at the same speed.
Maybe there is some factor of which we are totally unaware that affects the speed at which time flows. As the speed of flow changes, our perception rate changes along with it and it would appear to flow at a constant speed.
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Re: Expanding Universe
« Reply #24 on: 18/05/2005 12:49:01 »

 

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