Zeroth law
The zeroth law of thermodynamics may be stated as follows:
If system A and system B are individually in thermal equilibrium with system C, then system A is in thermal equilibrium with system B
The zeroth law implies that thermal equilibrium, viewed as a binary relation, is a Euclidean relation. If we assume that the binary relationship is also reflexive, then it follows that thermal equilibrium is an equivalence relation. Equivalence relations are also transitive and symmetric. The symmetric relationship allows one to speak of two systems being "in thermal equilibrium with each other", which gives rise to a simpler statement of the zeroth law:
If two systems are in thermal equilibrium with a third, they are in thermal equilibrium with each other
However, this statement requires the implicit assumption of both symmetry and reflexivity, rather than reflexivity alone.
The law is also a statement about measurability. To this effect the law allows the establishment of an empirical parameter, the temperature, as a property of a system such that systems in equilibrium with each other have the same temperature. The notion of transitivity permits a system, for example a gas thermometer, to be used as a device to measure the temperature of another system.
Although the concept of thermodynamic equilibrium is fundamental to thermodynamics, the need to state it explicitly as a law was not widely perceived until Fowler and Planck stated it in the 1930s, long after the first, second, and third law were already widely understood and recognized. Hence it was numbered the zeroth law. The importance of the law as a foundation to the earlier laws is that it allows the definition of temperature in a non-circular way without reference to entropy, its conjugate variable.
What does the Rigveda and Rudram say as part of celestial energy levels of Agni and Maruta:
I am not aware of any reference to Hanuman in the Rudram. namo
dUtAya is interpreted as a reference to agni, as indicated by
statements such as "agniM dUtaM vR^iNImahe", "we choose agni to
be our messenger (to Gods)." agni is frequently referred to as
a messenger who carries the offerings in the sacrifice to other
Gods.
In the R^ig Veda, however, Rudra is referred to in many places
as "pitar.h marutAM.h" meaning "Father of the Maruts, the storm
or wind Gods" and also "marutvAn.h", meaning "One who is attended
to by the Maruts." Rudra is therefore closely associated with the
Maruts in the R^ig Veda, while He is associated closely with agni
in the Yajur Veda, as in "rudro vA eshha yadagniH", "rudra is
indeed this agni (fire)."
From the background of HanumAn as the son of the wind God and the
fact that Rudra is mentioned as the Father of the Maruts, it is
possible to infer that HanumAn is an aMsha of Rudra/Shiva. Of course,
HanumAn may have been more directly identified as such in the
purANas or the various rAmAyaNa's -- I am not aware of a reference
offhand.
The second point you raise is the name vyuptakesha in the Rudram.
This is interpreted by sAyaNa as a sannyAsin in general, not the
sannyAsin Shankara, although sAyaNa belongs to Shankara's tradition.
BhaTTa BhAskara interprets vyuptakesha as either a yajamAna, a
performer of a sacrifice, who shaves his head as part of a sacrifice,
or a householder (gR^ihastha) who has to shave his head except
for a tuft of hair.
I have heard that abhinava Shankara says in his commentary on the
Rudram that vyuptakesha refers to Adi Shankara. But I do not have
this commentary with me at the moment.
