gjerawlins@watdaisy.UUCP (Greg Rawlins) (11/26/84)
["I don't want millions, I just want answers to my questions"] Here are some more questions that have kept me awake at night, can anyone out there in netland answer them for me? (1) - Over the past little while there's been a lot of discussion on the net of "semi-cosmological" issues, my question is extremely simple. How can we talk about events which occurred when the universe was 10**-43 seconds old? Can such a concept as TIME exist when all the things we use to measure it are coalesced into one huge ball of superhot matter? For example, the best timepieces we have right now are atomic clocks, can we speak about a "time" before even atoms existed? (2) - What justification is there for the omnipresent assumption that all sub-nuclear particles are the *same*. Are they indistinguishable because they are so small relative to any measuring device that any deviance cannot be detected? Or is it just an assumption about the sub-nuclear world that we've made and never thought about? ------ "These people were so amazingly primitive they still thought that digital watches were a pretty neat idea." -- /-----------------------------------------------------\ |Mail :Greg Rawlins :Department of Computer Science | | allegra\ U.of Waterloo,Waterloo,Ont.N2L3G1| | clyde \ \ | |UUCP :decvax ---- watmath --- watdaisy --- gjerawlins| | ihnp4 / / | | linus / | |CSNET:gjerawlins%watdaisy@waterloo.csnet | \-----------------------------------------------------/
tjr@ihnet.UUCP (Tom Roberts) (11/27/84)
[Two Answers]
(1) - Over the past little while there's been a lot
of discussion on the net of "semi-cosmological" issues, my
question is extremely simple. How can we talk about events
which occurred when the universe was 10**-43 seconds old? Can
such a concept as TIME exist when all the things we use to
measure it are coalesced into one huge ball of superhot
matter? For example, the best timepieces we have right now
are atomic clocks, can we speak about a "time" before even
atoms existed?
Time (and space) coordinate-systems are items of COGNITION, not
reality. They are used to THINK ABOUT and to DESCRIBE the real world,
but are not part of it (the things they describe, temporal and spatial
extent, are attributes of things in the real world).
Thus, a physicist does not require a timepiece in order to talk (or think)
about time. [There can be deep philosophical objections to this loose use
of language - I am avoiding mere technical jargon.] The subtleties involved
in discussing the first several seconds after the Big Bang are very
complicated, but do not invalidate the use of time in the discussion
(but you have to be VERY careful in specifying the coordinate-system).
(2) - What justification is there for the
omnipresent assumption that all sub-nuclear particles are
the *same*. Are they indistinguishable because they are so
small relative to any measuring device that any deviance
cannot be detected? Or is it just an assumption about the
sub-nuclear world that we've made and never thought about?
watdaisy!gjerawlins
I know of no claims that ALL sub-nuclear particles are the same. Let us
rather consider whether all (sub-nuclear) particles of the same type
are the same. That is: "are all X-particles identical", where X belongs to
the set of known (or possibly unknown?) sub-nuclear particles {pi+, pi0, pi-,
neutron, proton, mu+, neutrino(mu), up-quark(?), .........}. [The experimental
differences between these types of particles can be dramatic, even though they
are so very much smaller than the measuring devices.]
At one level, their identicalness is what permits us to define a
particle-type (all pi+ mesons act similarly, in similar situations, thus
we call all particles that act that way pi+ mesons). This is no different
from why we call cats "cats". [All possible situations must be considered,
in principle.]
At a deeper level, the theories that seem to describe the properties and
actions of these particles are symmetric under the interchange of any
two identical particles (that's what makes them identical). While there
is no guarantee that these theories are "correct", they do have strong
experimental support, and are theoretically elegant. [Yes, there is really
no known all-encompassing theory of elementary particles, but the partial
theories we do have exhibit this behavior, and there is reason to
believe that this property will carry over into the "ultimate" theory
(assuming there is one).] If there are no observable phenomena dependent
upon the interchange of two particles, they are identical (because that's
what the word means).
Tom Roberts
ihnp4!ihnet!tjrgwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (11/30/84)
Excellent questions! I frankly don't think the "big bang" theorists have properly considered such epistemological questions as what time MEANS in their models of the "first 10^-43 seconds of the universe". All subatomic particles of a given type are assumed to be identical because that leads to predictions that work. I'm sure someone will mention the idea of an anti-particle being a normal particle traveling "backward in time" in this context; that idea does not explain why all particles of a given type appear identical, though, since not every creation-annihilation interaction involves particle/anti-particle pairs.