| Topic: |
Science > Physics |
| User: |
"Nicolaas Vroom" |
| Date: |
05 Apr 2004 03:14:47 PM |
| Object: |
Re: open questions in physics |
"Nicolaas Vroom" <nicolaas.vroom@pandora.be> schreef in bericht
news:Ip_9c.54337$zC6.3552304@phobos.telenet-ops.be...
It is interesting so see that there are no comments
on these issues.
Apparently they are real issues and or no one knows
the answer.
In Nature Vol 428 March 2004 page 257 there is an article
"Shooting time's arrow" by Paul Davies.
This article is a book review of: "The fabric of Cosmos: Space
Time and the Texture of Reality" by Brian Greene which IMO
to a large extend also discusses "Open questions in physics".
However I have certain problems with this article.
The problem is that I can not agree with certain parts of the article.
But that does not mean what is written is wrong,
I mainly have certain doubts if it is correct.
The second line of this article reads:
"The laws of physics mean that the Universe is slowly dying."
The first question that pops is:
What is or means: "The laws of physics".
IMO "The laws of physics" is a piece of text which contains
a (mathematical) description of (a part of) the physical reality.
This description is based on observations and experiments.
If my interpretation is correct than the second line should
be read as:
"Observations (and Experiments) show that the Universe
is slowly dying"
I have a question: Which actual observations show that ?
or is this sentence a prediction? but than the word 'show' is wrong.
Next the article reads:
"His prediction was based on the second law of thermodynamics"
"The basis of the dying Universe is easy to explain.
We are surrounded by processes that have a
definite directionality to them : people grow old etc"
"The same directionality pervades the cosmos.
The Sun, .... will burn out and die"
But this are rather local observations.
Are those observations justifiable, valid to make any
prediction for what is happening to the total Universe ?
Next the article reads:
"But this incontestable fact conceals a deep Mystery.
The world about us may display a conspicuous 'Arrow of
Time', but the underlying laws of physics are,
with a minor exception, completely symmetric"
I have in this respect a problem with Newton's Law.
Using Newton's Law and using a set of initial conditions at t0
you can predict the future of n objects at t1 (and the past and t-1)
However if two of those objects collide at t2 and you are left
with n-1 objects at t3 than you have a problem if you want
start with the initial conditions at t3
and you want to calculate the past at t0.
In that sense it makes not much sense to call Newton's Law
symmetric.
Next the article reads:
"Greene even tackles, but does not resolve, the vexed issue
of the flow of time - that most familiar of human experiences,
which is bafflingly absent from physicists description of the world"
IMO Greene and the physicists are correct.
There exists not flow of time. What does it mean.
The only thing you can say is that the Universe exits
and that the Universe evolves i.e. constantly changes.
Next: "One way to think of the cosmic arrow of time is to
regard the Universe as a gigantic clock slowly running down.
The problem is to explain how it was wound up
in the first place"
Partly. The problem is how the Universe started in the first place.
The compare the Universe with a clock does not help you.
Neither does the second law of thermodynamics.
Next: "We have available a snapshot of the Universe shortly
after its birth, in the formal of a thermal map of the sky etc.
The data show the fading afterglow of the BB and enables
cosmologists to reconstruct the details of its primordial
thermodynamic state."
Next: "The young Universe was close to thermodynamic equilibrium"
That means: in the details there is not much detail to observe.
Next: "then how has it come alive again and achieved
such a low-entropy state today?"
I expect they mean: complexity i.e. non equilibrium state.
May be part of the solution is that the thermal map we observe
to day is not a good image of the state of the Universe
380.000 years after birth.
Next: "Greene correctly identifies the solution of this puzzle.
The key lies with gravity.
This universal force seizes any tiny irregularity in the
distribution of matter and amplifies it."
But how do we know that. What means gravity.
What are the observations on which this is based ?
IMO you can not use Newton's Law (which describes
how planets move around the Sun) to explain that.
At the end of that paragragh:
"Our very existance depends on the entropy gap that
this has created".
I do not understand.
Next: "Today, however there is a ready explanation
in the form of the 'inflationary Universe' scenario etc.
Any pre-existiting irregularities would have been smoothed
away by this abrupt and huge swelling of space"
IMO with the same trust you can also say the opposite.
Next: "This pleasing conclusion immediatly begs the question
of what preceded inflation and why it happened at all etc"
I fully agree that is the issue, but that is also difficult to answer.
Exactly because of this I have great doubts in easy
sententences like: "The key lies with gravity."
Near the end: "Modern physics has shown that space and time
are, in fact, things, just as particles of matter are things."
Why introducing terms like: things.
Particles of matter are objects.
To call time an object requires clarification, including why.
A clock is an object but that is not the same as time.
IMO the whole subject (article) is a litle bit of everything
without any clear coherent story.
IMO a lot around the BB is still an "open question in physics".
I expect it will be like that for a long time (period) to come.
Starting point should be distinction between what we know,
based on observations and experiments,
and what we do not know (i.e. mostly speculations)
Nicolaas Vroom
http://users.pandora.be/nicvroom/
.
|
|
|
Related Articles |
|
|
