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Here are my questions concerning ...

http://arXiv.org/abs/0903.1474

Soft Physics from RHIC to LHC

Peter Steinberg

------- Comparing the relevant energy and space-timescales implied by the success of the

hydrodynamical models, the matter at RHIC is formed under quite extreme conditions.

The formation time needed for the hydrodynamic calculations is τ0 =0.6fm/c, or

approximately 2 yoctoseconds (10−24) [11]. This number is far smaller than the time

taken a massless particle to traverse the radius of a hadron(τ ∼1fm/c)[12]. The same

calculations determine that the energy density needed to match the data is around ϵ

∼30 GeV/fm3, about 60 times the density of a nucleon in its rest frame, ϵN ∼500MeV/fm3 .

It should be noted that these estimates do not preclude even higher energy densities at

even earlier times.

One empirically observed feature that should shed light on this is “extended longitudinal scaling”[17]. It

has been observed in proton-proton collisions that the pseudo rapidity density (dNch/dη)

of inclusive charged particle production is energy-independent when viewed in a frame where one or other of the incoming particles is at rest [18]. This is done by using the kinematic variable η′ =η

−ybeam, where ybeam is the rapidity of one of the beams. Results for dN/dη′ are shown for Au+Au collisions at four RHIC energies[19] in the left panel of Fig. 4, where longitudinal scaling is clearly observed.The persistence of this scaling over a factor of ten in energy suggests that no major changes in the particle production occurs over this range.

This suggests that the geometrical conﬁguration of the participants is “frozen in” immediately, consistent with the previous estimates of τo r perhaps even shorter times.

My understanding of this paper is that once a perfect liquid state has been achieved that this perfect liquid will continue to exist over a large range of density, temp. I don’t see how any changes of those variables can be observed from inside the horizon of the universe. (Irrigardless of your belief in a finite or infinite universe.)

A change that is progressing at c, and heading towards you cannot be observed nor can you observe a change progressing at c, that is going away from you.

You cannot see a photon coming towards you nor a photon going away from you.

Therefore, “change” appears to be “immediate”.

If the geometry is “frozen in” then only an external clock can record the passage of time. From the point of view of the internal observer, change occur “immediately” yet the existing prior conditions could have existed for an extremely long period of “external time”. “Changes” in the universe could have been “progressing” for a long time and there would be no way of being aware of it and of measuring the “progression”.

If correct, how would this change our views of the time frame of the evolution of the early universe prior decoupling?

My second question is ...

What is temp. and how can it be measured when in a perfect liquid state where “the geometry is frozen in”?

(Yes, I looked up the wiki discussion on temp.)

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

===== For a system in thermal equilibrium at a constant volume, temperature is thermodynamically defined in terms of its energy (E) and entropy (S).

It is also possible to define temperature in terms of the second law of thermodynamics, which deals with entropy. Entropy is a measure of the disorder in a system.

The argument in the previous section is how the relation between entropy and heat was arrived at historically. Modern definition of temperature is given in Statistical mechanics and it is defined in terms of the fundamental degrees of freedom of a system (see the article entropy for details). Eq.(8) of the previous section is then taken to be the defining relation of the temperature. Eq. (7) can be derived from the definition of entropy.

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# The geometry is frozen in

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