Physicists and astronomers use conventional units of time in speaking
of the Big Bang ("one second after the Big Bang", etc.). But how
meaningful are such statements? If time and space are local and depend
on the relative velocity of the observer, how can our own local
definitions of time (seconds, minutes) be used to describe an interval
of "time" during Big Bang conditions? If I were to ask whether the
first "second" after the Big Bang was of the same duration as an
earth-based second, would it be a meaningful question?

(Wendy Yamamoto) wrote in message


If I were to ask whether the first "second" after the Big Bang
was of the same duration as an earth-based second, would
it be a meaningful question?

Yes.

-- Jim

Wendy Yamamoto:
Physicists and astronomers use conventional units of time in speaking
of the Big Bang ("one second after the Big Bang", etc.). But how
meaningful are such statements?

That depends. Unless something very surprising pops up, what happened
on the order of a second is pretty sound. By looking at the current
temperature and size of the universe and then extrapolating backwards,
it's possible to get much more detailed than one second. We know the
strength of the weak and strong interactions and since unification
of those forces happens at specific temperatures, it's fairly straight
forward to provide a picture of the universe beginning around the
first 10^-40 seconds or so. Steven Weinberg's book, "The First Three
Minutes" gives a very good and easy to read account of exactly what
the title describes.

If time and space are local and depend on the relative velocity of the
observer, how can our own local definitions of time (seconds, minutes)
be used to describe an interval of "time" during Big Bang conditions?

Measurements made by different observers can be reconciled because
relativity describes the relationship. Essentially, all observers
should agree that the universe started at the same time.

If I were to ask whether the first "second" after the Big Bang was of
the same duration as an earth-based second, would it be a meaningful
question?

That again depends. If there are no surprises, then presumably a second
is a second is a second, at least until you get below 10^-40 (or perhaps
10^-50) seconds or so. At that point, I'm not sure it would be meaningful
to think of the universe in those terms. That would be the era of quantum
gravity and neither E&M or nuclear forces would have existed.

(Jim Jastrzebski) wrote in message ...
(Wendy Yamamoto) wrote in message


If I were to ask whether the first "second" after the Big Bang
was of the same duration as an earth-based second, would
it be a meaningful question?

Yes.

-- Jim

xxein: Very good question. Now, through phase generations, how is
our universe at present to be compared?

Because all observers are attached to galaxies, everyone is assumed to
be moving along with the bulk flow matter in an expanding universe. So
everyone agrees to the meaning of "cosmic time."

http://www.everythingimportant.org/r...multaneity.htm

Eugene Shubert

(Bilge) wrote in message ...
Wendy Yamamoto:
Physicists and astronomers use conventional units of time in speaking
of the Big Bang ("one second after the Big Bang", etc.). But how
meaningful are such statements?

That depends. Unless something very surprising pops up, what happened
on the order of a second is pretty sound. By looking at the current
temperature and size of the universe and then extrapolating backwards,
it's possible to get much more detailed than one second. We know the
strength of the weak and strong interactions and since unification
of those forces happens at specific temperatures, it's fairly straight
forward to provide a picture of the universe beginning around the
first 10^-40 seconds or so. Steven Weinberg's book, "The First Three
Minutes" gives a very good and easy to read account of exactly what
the title describes.

If time and space are local and depend on the relative velocity of the
observer, how can our own local definitions of time (seconds, minutes)
be used to describe an interval of "time" during Big Bang conditions?

Measurements made by different observers can be reconciled because
relativity describes the relationship. Essentially, all observers
should agree that the universe started at the same time.

Big Bang assumes that the worldline of all particles started at the
same point. Threfore you can observe the univerese from the
perspective of any particle (or object) and use its time.


If I were to ask whether the first "second" after the Big Bang was of
the same duration as an earth-based second, would it be a meaningful
question?

That again depends. If there are no surprises, then presumably a second
is a second is a second, at least until you get below 10^-40 (or perhaps
10^-50) seconds or so. At that point, I'm not sure it would be meaningful
to think of the universe in those terms. That would be the era of quantum
gravity and neither E&M or nuclear forces would have existed.
Second is measured by clock. Time in General Relativity is also
defined by clock. Therefore 3 second is allways the same length of
time by definition.

György

You say "If there are no surprises, then presumably a second is a
second is a second . . ." But wait. Let's take a conventional
illustration of relativity, in which one twin brother leaves earth in
a rocket and approaches the speed of light in it. After a few
rocket-days, he returns to earth, only to find his earth-twin (and
everybody else) greatly aged. This is a trip taken in contemporary
time and conditions. Yet a second wasn't a second at all. The seconds
were relative. But in this case, I assume a mathematical correlation
could easily be drawn between a rocket-second and an earth-second. If
I understand you correctly, you are asserting that a similar
correlation can be drawn between a Big Bang second and an earth-second
using a scale provided by the unity of forces that occurs at a certain
"temperature". Has anyone ever done so? I for one would find it quite
interesting to learn that the first second after the Big Bang was
equivalent to (say) a thousand earth-years --- or whatever the
correlation is!

On 8/28/2003 2:59 AM, Wendy Yamamoto wrote:
Let's take a conventional
illustration of relativity, in which one twin brother leaves earth in
a rocket and approaches the speed of light in it. After a few
rocket-days, he returns to earth, only to find his earth-twin (and
everybody else) greatly aged. This is a trip taken in contemporary
time and conditions. Yet a second wasn't a second at all.

Sure it is, when considered LOCALLY. To each twin, for every second
along their journey, clocks behave as normal, and at all times a
collocated and comoving standard clock will agree with the twin's clock.

What relativity requires one to do is abandon the notion of "universal
time". Elapsed proper time can VARY for different trajectories, even
though standard clocks are used throughout. It really does not make
sense to try to fit that into a statement like "a second wasn't a
second" -- each second WAS a second, it's just thar your statment makes
assumptions about seconds (really "time") that do not hold (in either SR
or the real world).


The seconds
were relative.

Not to either twin -- they each observed normal seconds on their own
clock. You need to learn to not make global or absolute assumptions.


I for one would find it quite
interesting to learn that the first second after the Big Bang was
equivalent to (say) a thousand earth-years --- or whatever the
correlation is!

The first second after the big bang (implicitly measured in the
conventional way along the trajectory of one of the dust particles) was
of the same duration as a second now. The physical conditions during
that second were VERY different from the conditions today. Because of
that, there is no useful "equivalence" between them.


Tom Roberts

Wendy Yamamoto:
You say "If there are no surprises, then presumably a second is a
second is a second . . ."

Actually, what I meant by surprises was something a little more
exotic, but ok...

But wait. Let's take a conventional
illustration of relativity, in which one twin brother leaves earth in
a rocket and approaches the speed of light in it. After a few
rocket-days, he returns to earth, only to find his earth-twin (and
everybody else) greatly aged. This is a trip taken in contemporary
time and conditions. Yet a second wasn't a second at all. The seconds
were relative.

That was the reason I qualified my statements with:

"Measurements made by different observers can be reconciled because
relativity describes the relationship. Essentially, all observers
should agree that the universe started at the same time."

Relativity provides the relationship between the observers which allows
them to compare their measurements of the same phenomena.

But in this case, I assume a mathematical correlation could easily be
drawn between a rocket-second and an earth-second.

You are missing the point of relativity. Relativity does not say that
those seconds are different. Relativity says that those seconds are the
same. What differs is the number of seconds (proper time) which each twin
"travels". This is precisely the same relationship as occurs when
traversing two different routes between points A and B. One route may be
the shortest distance between A and B and the other route may take many
twists and turns, so that the elapsed distance on the odometers differs.
In that case, one does say that the miles are longer along one route or
the other. One says that the miles are the same distance, but the route is
longer. In special relativity, the length of the "route" is the elapsed
proper time givent by (d\tau)^2 (or (ds)^2 if you prefer), not the
coordinate time.

If I understand you correctly, you are asserting that a similar
correlation can be drawn between a Big Bang second and an earth-second
using a scale provided by the unity of forces that occurs at a certain
"temperature". Has anyone ever done so?

Sure. The unification scale for the electroweak interaction occurs
at energy determined by the mass of the W and Z, around a 100 GeV.
Estimate the temperature via E = kT and you get a temperature of
af about 10^15 K. The situation is not so clearcut for unification
with the strong force, but the masses of those gauge boson is presumed
to be on the order of 10^16 GeV, which places the temperature at the
order of 10^28 K. Gravity is expected to be unified at the energy of the
planck mass, which is around 10^19 GeV which is a temperature of about
10^32 K. Now, if you take the planck time to be the time at which
gravity separates from the oother three forces, you have a time of
10^-44 seconds. From the temperature and statistical mechanics, you
can determine how much the universe would have expanded in order to
cool to the temperature at which thestrong interaction separated from
the electroweak and then the electromagnetic force separated from the
weak force. From this you can determine how large the universe had to
be before atoms could form so that the universe becoms transparent to
the electromagnetic radiation (e.g. light) that is what we see as the
cosmic microwave background radiation.

I for one would find it quite interesting to learn that the first second
after the Big Bang was equivalent to (say) a thousand earth-years --- or
whatever the correlation is!

One could speculate about those sorts of things but in reality, it
doesn't really make sense to do so. We _define_ a second, so essentially,
the value we give for the passage of time is what it means in our terms.
The one place such speculation might be considered is during inflation,
which is called inflation because in our view of looking at things, the
universe expanded much more rapidly than the speed of light, which is how
we define a second. It's not clear to me that this definition is really
meaningfull during that era and that inflation is more a product of
definition than what would be called inflation to "observers" at that era,
but that is rather speculative and I haven't looked at inflation enough to
see whether the reason it's not clear is simply due to not knowing enough
about it for it to be clear.

=?ISO-8859-1?Q?Gy=F6rgy_Szondy?=:
(Bilge) wrote in message ...
Wendy Yamamoto:
Physicists and astronomers use conventional units of time in speaking
of the Big Bang ("one second after the Big Bang", etc.). But how
meaningful are such statements?

That depends. Unless something very surprising pops up, what happened
on the order of a second is pretty sound. By looking at the current
temperature and size of the universe and then extrapolating backwards,
it's possible to get much more detailed than one second. We know the
strength of the weak and strong interactions and since unification
of those forces happens at specific temperatures, it's fairly straight
forward to provide a picture of the universe beginning around the
first 10^-40 seconds or so. Steven Weinberg's book, "The First Three
Minutes" gives a very good and easy to read account of exactly what
the title describes.

If time and space are local and depend on the relative velocity of the
observer, how can our own local definitions of time (seconds, minutes)
be used to describe an interval of "time" during Big Bang conditions?

Measurements made by different observers can be reconciled because
relativity describes the relationship. Essentially, all observers
should agree that the universe started at the same time.

Big Bang assumes that the worldline of all particles started at the
same point. Threfore you can observe the univerese from the
perspective of any particle (or object) and use its time.

You missed the point. What she was asking was in regard to observers
who have relative velocities with respect to each other and therfore
must reconcile their measurements. Those observers will see the same
phenomena differently. That is why I qualified that the way I did.
Had I simply left it as you've stated it, I wouldn't have answered the
question being asked.

That again depends. If there are no surprises, then presumably a second
is a second is a second, at least until you get below 10^-40 (or perhaps
10^-50) seconds or so. At that point, I'm not sure it would be meaningful
to think of the universe in those terms. That would be the era of quantum
gravity and neither E&M or nuclear forces would have existed.

Second is measured by clock. Time in General Relativity is also
defined by clock. Therefore 3 second is allways the same length of
time by definition.

What do you define as a clock when there is nothing to use as a
standard clock? We use the speed of light, but since light did not
exist before electroweak symmetry breaking, this is obviously not
a universal definition. One could presume the constant c is more
fundamental that the phenomena to which it applies, but I think that
can only be justified to a point and I am not sure it can be justified
at all prior to the planck time. If general relativity breaks down
at the planck time, then I don't think that you have any real means
of defining time and distance in any way that resembles the definitions
used in general relativity.