How will the universe end - with a bang or with a whimper?

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Profile Julie
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Message 1518264 - Posted: 19 May 2014, 17:04:37 UTC - in response to Message 1518262.  

Good post. In which case we are both correct. But I still have difficulty with this word or phrase "space-time". Space is one thing, time is another, I don't recognise space-time as a single entity. I also have difficulty with this "curved" space, and other apparent forms of it. Space is space is space, it is a void.

Space to me is three dimensional, it is the volume within a sphere, within which everything exists. Except that the boundary or outer surface of this sphere which we call the universe is infinite, i.e. it has no end.



When I thought of the Universe as a kid, I also thought of it in a three dimensional way. The fact is though that the Universe is thought to have 11 dimensions. We can hardly grasp the fourth dimension, let alone the remaining 7!
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Message 1518280 - Posted: 19 May 2014, 17:24:30 UTC - in response to Message 1518276.  

In theoretical physics, M-theory is an extension of string theory in which 11 dimensions of spacetime are identified as 7 higher-dimensions plus the 4 common dimensions (11D st = 7 hd + 4D). Proponents believe that the 11-dimensional theory unites all five 10-dimensional string theories (10D st = 6 hd + 4D) and supersedes them. Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

All looks good on paper, so of course must be right, else there would be a lot of red faced theoretical mathematicians. Everyone has the freedom to believe in what they want. Yes of course we should be pushing the boundaries of physics and mathematics, but's let's try and keep our feet on the ground as we do so.


Yes, we must do 'research' but we have to stay with both feet on the ground:)
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Message 1518288 - Posted: 19 May 2014, 17:40:43 UTC - in response to Message 1518280.  

In theoretical physics, M-theory is an extension of string theory in which 11 dimensions of spacetime are identified as 7 higher-dimensions plus the 4 common dimensions (11D st = 7 hd + 4D). Proponents believe that the 11-dimensional theory unites all five 10-dimensional string theories (10D st = 6 hd + 4D) and supersedes them. Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

All looks good on paper, so of course must be right, else there would be a lot of red faced theoretical mathematicians. Everyone has the freedom to believe in what they want. Yes of course we should be pushing the boundaries of physics and mathematics, but's let's try and keep our feet on the ground as we do so.


Yes, we must do 'research' but we have to stay with both feet on the ground:)


...not tucked up beside us in our armchairs? :)
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Message 1518290 - Posted: 19 May 2014, 17:41:56 UTC - in response to Message 1518288.  

In theoretical physics, M-theory is an extension of string theory in which 11 dimensions of spacetime are identified as 7 higher-dimensions plus the 4 common dimensions (11D st = 7 hd + 4D). Proponents believe that the 11-dimensional theory unites all five 10-dimensional string theories (10D st = 6 hd + 4D) and supersedes them. Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

All looks good on paper, so of course must be right, else there would be a lot of red faced theoretical mathematicians. Everyone has the freedom to believe in what they want. Yes of course we should be pushing the boundaries of physics and mathematics, but's let's try and keep our feet on the ground as we do so.


Yes, we must do 'research' but we have to stay with both feet on the ground:)


...not tucked up beside us in our armchairs? :)


Ok...that too:))
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Message 1518309 - Posted: 19 May 2014, 18:05:18 UTC
Last modified: 19 May 2014, 18:06:39 UTC

The real problem of modern physics is cost. New theories don't cost much but experimental apparatus needed to proof or disproof them costs a huge amount of money. Of course, you can run a computer simulation, like those of Test4Theory@home but any simulation is based on hypotheses, contrarily to what Newton said in his beautiful Latin: Hypotheses non fingo.
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Message 1518317 - Posted: 19 May 2014, 18:31:25 UTC - in response to Message 1518262.  

surface of this sphere which we call the universe is infinite, i.e. it has no end.


The surface is finite as are the inner 3-dimensions. It is UNBOUNDED but it is not infinite.
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Message 1518326 - Posted: 19 May 2014, 18:38:36 UTC

I think this universe will eventually end in a big rip. This is because the continuous expansion of the universe is accelerating.
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Message 1518332 - Posted: 19 May 2014, 18:48:01 UTC - in response to Message 1518326.  
Last modified: 19 May 2014, 18:48:30 UTC

This is based on observations of "standard candles", that is Ia supernovae. What if we don't know enough of supernovae?
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Message 1518357 - Posted: 19 May 2014, 19:37:43 UTC - in response to Message 1518332.  

This is based on observations of "standard candles", that is Ia supernovae. What if we don't know enough of supernovae?
Tullio


There very well might be aspects of supernova mechanics that we have yet to unlock. But the study of supernovas has been been ongoing since we've been able to recognize them as such and continues to this day so i believe most scientists have accepted the standard candle axiom and feel confident making predictions from it.
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Message 1518375 - Posted: 19 May 2014, 20:06:31 UTC - in response to Message 1518262.  
Last modified: 19 May 2014, 20:17:05 UTC

Good post. In which case we are both correct. But I still have difficulty with this word or phrase "space-time". Space is one thing, time is another, I don't recognise space-time as a single entity. I also have difficulty with this "curved" space, and other apparent forms of it. Space is space is space, it is a void.

Space to me is three dimensional, it is the volume within a sphere, within which everything exists. Except that the boundary or outer surface of this sphere which we call the universe is infinite, i.e. it has no end.


I don't know what to say to that because there might be a semantics issue between your definition of space and the model scientists define as space-time. The idea of space-time is essential to relativity but we do know that relativity is not complete so maybe a TOE/GUT will be able to separate space and time like it was before Einstein.

As far as curved space, that is pretty easy to visualize. Draw a right triangle on a piece of paper, the sum of its interior angles is equal to 180 degrees. Now, instead of paper we will draw a right triangle on the surface of the earth; draw a horizontal line on the equator that goes 1/4 of the way around the globe, from one endpoint draw a line to the north pole, now connect the north pole to the other endpoint of the equator line. You have just drawn a triangle whose interior angle sum is greater than 180 degrees (270 degrees actually). That is the most basic form of curved space, a 2d curved space.
To my understanding the curvature of space-time is what makes time pass at a slower rate near a massive body than it does far away from the massive body. This is why GPS satellites have to take relativity into account when syncing their clocks with clocks on earth.
Please pardon me if this was stuff you already knew. It might have arisen from a misinterpretation of your post.
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Message 1518554 - Posted: 20 May 2014, 3:10:41 UTC - in response to Message 1518385.  

To my understanding the curvature of space-time is what makes time pass at a slower rate near a massive body than it does far away from the massive body.

That is the gravity effect. Time dilation occurs at speeds away from the observed and the observer.


Yes, it is the gravity effect, and gravity is the acceleration caused by the curvature of space-time, right? I think that is the proper interpretation of Einstein's model, or did i miss something?
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Message 1518583 - Posted: 20 May 2014, 5:04:20 UTC - in response to Message 1518357.  

This is based on observations of "standard candles", that is Ia supernovae. What if we don't know enough of supernovae?
Tullio


There very well might be aspects of supernova mechanics that we have yet to unlock. But the study of supernovas has been been ongoing since we've been able to recognize them as such and continues to this day so i believe most scientists have accepted the standard candle axiom and feel confident making predictions from it.

True, but NASA has just launched a campaign of observations on supernovae using the Kepler spacecraft, built for observing exoplanets. This means there is still something we do not know about them.
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Message 1518642 - Posted: 20 May 2014, 7:31:14 UTC - in response to Message 1518583.  

This is based on observations of "standard candles", that is Ia supernovae. What if we don't know enough of supernovae?
Tullio


There very well might be aspects of supernova mechanics that we have yet to unlock. But the study of supernovas has been been ongoing since we've been able to recognize them as such and continues to this day so i believe most scientists have accepted the standard candle axiom and feel confident making predictions from it.

True, but NASA has just launched a campaign of observations on supernovae using the Kepler spacecraft, built for observing exoplanets. This means there is still something we do not know about them.
Tullio


Oh definitely, that's what i meant when i said "continues to this day", we still have a lot to learn. I just don't think they would be basing so many measurements using the standard candle idea if they weren't fairly confident in that aspect of their knowledge, but i'm not an astrophysicist (yet) so i'm not really qualified to say what they do and don't know i'm just basing that assumption on the argument i just presented.
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Message 1518644 - Posted: 20 May 2014, 7:32:42 UTC - in response to Message 1518640.  
Last modified: 20 May 2014, 7:41:08 UTC

I think there are masses of things we don't know about everything, the best we can do is theorise with the knowledge that we have at the moment.


Agreed, that's the best we can do.

[edit] Again I refer to Aristoteles, Plato, Copernicus, Hubble et others
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Message 1518652 - Posted: 20 May 2014, 7:45:18 UTC - in response to Message 1518640.  

I think there are masses of things we don't know about everything, the best we can do is theorise with the knowledge that we have at the moment.


True, there a lot to learn; there's probably a lot more that we don't know that what we know especially considering the consensus is that both QM and relativity are incomplete. But when theories are proposed that give us predictions that we can test, confirm, and apply we catch a glimpse of how the universe really works, as strange and unintuitive as it might be, and that's what ,IMO, relativity and QM have done.
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Message 1518664 - Posted: 20 May 2014, 8:12:31 UTC - in response to Message 1518652.  

I think there are masses of things we don't know about everything, the best we can do is theorise with the knowledge that we have at the moment.


True, there a lot to learn; there's probably a lot more that we don't know that what we know especially considering the consensus is that both QM and relativity are incomplete. But when theories are proposed that give us predictions that we can test, confirm, and apply we catch a glimpse of how the universe really works, as strange and unintuitive as it might be, and that's what ,IMO, relativity and QM have done.

I recently put a question to prof. Roberto Battiston of Trento University, who has just been nominated President of Italian Space Agency and he was kind enough to answer me in his blog at Le Scienze online magazine. Le Scienze is the Italian version of Scientific American, and I have been a visiting editor of it. The question was. if an hydrogen atom emits a photon, say in the Lyman-alpha emission, are they entangled? Yes, he answered, even if the hydrogen atom falls inside an event horizon (say a black hole). This is one of the mysteries of quantum mechanics, he said.
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Message 1518674 - Posted: 20 May 2014, 8:34:22 UTC - in response to Message 1518664.  

I think there are masses of things we don't know about everything, the best we can do is theorise with the knowledge that we have at the moment.


True, there a lot to learn; there's probably a lot more that we don't know that what we know especially considering the consensus is that both QM and relativity are incomplete. But when theories are proposed that give us predictions that we can test, confirm, and apply we catch a glimpse of how the universe really works, as strange and unintuitive as it might be, and that's what ,IMO, relativity and QM have done.

I recently put a question to prof. Roberto Battiston of Trento University, who has just been nominated President of Italian Space Agency and he was kind enough to answer me in his blog at Le Scienze online magazine. Le Scienze is the Italian version of Scientific American, and I have been a visiting editor of it. The question was. if an hydrogen atom emits a photon, say in the Lyman-alpha emission, are they entangled? Yes, he answered, even if the hydrogen atom falls inside an event horizon (say a black hole). This is one of the mysteries of quantum mechanics, he said.
Tullio


However, less information is available about the degree of polarization entanglement between the two photons if an arbitrary geometry is considered for collecting the photons.
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Message 1518676 - Posted: 20 May 2014, 8:46:57 UTC - in response to Message 1518674.  



However, less information is available about the degree of polarization entanglement between the two photons if an arbitrary geometry is considered for collecting the photons.

My example considered an atom and a photon.
Tullio
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Message 1518679 - Posted: 20 May 2014, 8:57:09 UTC - in response to Message 1518676.  
Last modified: 20 May 2014, 9:02:36 UTC



However, less information is available about the degree of polarization entanglement between the two photons if an arbitrary geometry is considered for collecting the photons.

My example considered an atom and a photon.
Tullio


I know Tullio:) I was just wondering about the entanglement between photons obtained from the two-photon decay of atomic hydrogen
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Message 1518706 - Posted: 20 May 2014, 12:10:53 UTC

If it were to turn out that type 1a supernovas are not as consistent as currently believed it sure would throw a lot of what is thought to be known out the window.
Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.
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Message boards : SETI@home Science : How will the universe end - with a bang or with a whimper?


 
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