They say time is what the clock measures and time is something
that has already happened. But i've been continued puzzled about
what time really is. How come physicists explore the possibility of
time travel. How can you go back to the past when it has already
happened. In newtonian argument, it may be as plain as this. But
in light of SR and GR. Time seems to be something more and
has an almost magical quality to it. Can you describe time in
such a way that it can make time travel makes sense (theoretically
speaking)?

Rex

On Fri, 24 Aug 2007, Rex wrote:

They say time is what the clock measures and time is something
that has already happened. But i've been continued puzzled about
what time really is.

Welcome to philosophy!

How come physicists explore the possibility of
time travel.

They usually don't. Around here, about 0% of physicists explore the
possiblity of time travel. A small number might explore it (a) because
they're interested, and it's interesting (interesting enough for you to
post about it), and (b) it sells pop-sci books.

How can you go back to the past when it has already
happened. In newtonian argument, it may be as plain as this. But
in light of SR and GR. Time seems to be something more and
has an almost magical quality to it.

In light of SR, time depends on people's clocks, not just on "God's
clock", as per Newton. Still, no time travel. AFaIUT, GR allows time
travel in that certain geometries of spacetime are permitted by the
equations, but there isn't necessarily any reason why they might exist.

Can you describe time in
such a way that it can make time travel makes sense (theoretically
speaking)?

No. But perhaps I am over-influenced by the likes of Kramers and Kronig.

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/...,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html

Rex wrote:

They say time is what the clock measures.
[snip]

If you don't like oscillators, go for radioactive decay.

How come physicists explore the possibility of
time travel.
[snip]

Grant funding. They'd go spelunking after canthariasis if it could be
modeled, funded, and published.

How can you go back to the past when it has already
happened.

Who says? The Earth is only 6000 years old. GOD said so. All the
overwhelming evidence for a 5 billion year old Earth was emplaced by
time travel. Is that made plain enough for you?

In newtonian argument, it may be as plain as this. But
in light of SR and GR. Time seems to be something more and
has an almost magical quality to it. Can you describe time in
such a way that it can make time travel makes sense (theoretically
speaking)?

The universe demands causality. No time travel except across
realities wherein it already happened. Niven diddled with the concept
some 35 years ago, "The Theory and Practice of Time Travel" in "All
the Myraid Ways", 1971. Catch up on your reading.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2

On Aug 24, 6:19 pm, Rex wrote:
They say time is what the clock measures and time is something
that has already happened. But i've been continued puzzled about
what time really is. How come physicists explore the possibility of
time travel. How can you go back to the past when it has already
happened. In newtonian argument, it may be as plain as this. But
in light of SR and GR. Time seems to be something more and
has an almost magical quality to it. Can you describe time in
such a way that it can make time travel makes sense (theoretically
speaking)?


No I can't, but I think I can explain why such a concept arises.

Space is a relational concept. There is no absolute space, there are
only spatial relationships betwen objects.

When you get get to some "place" that seems to be some "place" that
you've been before - that's an illusion.

Let's say you visit Trafalgar square, which isn't really a "place" -
it's a collection of objects in certain spatial relationships with
respect to each other and the Earth and with the Sun.

"Return" to Trafalgar Square 6 months later and that "place" has moved
186 million miles wrt the Sun and the Sun has moved further still wrt
the Gakaxy. The Galaxy itself as moved..... ... and so on.

So you're not really in the same "place".

If you stay in the same "place" wrt the Sun, you'll find that the
Earth quickly leaves you behind.


Time is also a relational concept. There is no absolute time, there
are only temporal relationships amongst objects.

If you stay fixed at some time, you'll quickly find that the Earth has
left you behind.

These relational concepts are not well understood.

No rational person would think that if you went back to some "relative
location in space" (Trafalgar Square) the same people would be there
as were there on your last visit.

Yet those same otherwise rational persons think that if they go back
to some "relative location in time" that their grandfather would still
be there and they could kill him.

Love,
Jenny

"Rex" wrote in message
ups.com...
:
: They say time is what the clock measures and time is something
: that has already happened. But i've been continued puzzled about
: what time really is. How come physicists explore the possibility of
: time travel. How can you go back to the past when it has already
: happened. In newtonian argument, it may be as plain as this. But
: in light of SR and GR. Time seems to be something more and
: has an almost magical quality to it. Can you describe time in
: such a way that it can make time travel makes sense (theoretically
: speaking)?
:
: Rex

The magical quality is this:

'we establish by definition that the "time" required by
light to travel from A to B equals the "time" it requires
to travel from B to A' because I SAY SO and you have to
agree because I'm the great genius, STOOOPID, don't you
dare question it. -- Albert Einstein,
who in 1895 failed an examination that would have allowed
him to study for a diploma as an electrical engineer at
the Eidgenössische Technische Hochschule in Zurich
(couldn't even pass the SATs).

"Counterfactual assumptions yield nonsense.
If such a thing were actually observed, reliably and reproducibly, then
relativity would immediately need a major overhaul if not a complete
replacement." -- Tom Roberts.

Dear Rex:

"Rex" wrote in message
ups.com...

They say time is what the clock measures and
time is something that has already happened.
But i've been continued puzzled about what time
really is. How come physicists explore the
possibility of time travel. How can you go back
to the past when it has already happened.

More to the point, what happens to this Universe, if your mass is
*duplicated exactly* for some period of time in the past.

In newtonian argument, it may be as plain as
this. But in light of SR and GR. Time seems
to be something more and has an almost
magical quality to it.

.... just like a little ball of mercury ...

Can you describe time in such a way that it
can make time travel makes sense (theoretically
speaking)?

Let's say that from the Big Bang to the distant diffuse end of
the Universe, is a trip from the event horizon of a black hole to
its "central singularity". A trip back in time would be
exceeding the speed of light, opening up a direction that no
light ever comes from, and moving back towards the event horizon
(a surface you cannot see or be aware of).

So I guess the answer is "no, I cannot".

David A. Smith

"Rex" escreveu na mensagem
ups.com...

They say time is what the clock measures and time is ...


Time is very relative. It greatly depends on the situation you are into.
One clock minute with your girl friend looks like a blink of an eye, but
that same minute sited on mama's strove looks like an eternity.
That's what Einstein had explained us. It depends on the situation.
When you get to much speed, time for you will look slower, up to the
maximum speed "c", where time will stop (don't horry, at such speed you are
already dead, for sure).

Actually, it is the quantity "vt" that always remains constant (being "v"
your velocity and "t" GOD's time).
Otherwise space will have to expand, or contract, since the quantity "vt"
actually is a quantity measured in meters (it's a distance).
Therefore you can chose between time to change, or distance to change.
Never both at the same time.

For instance, your want to go around the world.
You can take a fast plane and it will take you several hours.
Or else, you can walk and it will take you Years.
All that you want is to go around the world (a distance), then the
time that takes depends on the speed you have.

They say time is what the clock measures and time is ...



Time is dimension and nothing more than that, it is just that simple.

Time is the 4th dimension and in my opinion it is probabilistic, as is
length.

Furthermore, in my opinion, there is no need for the concept of energy if
one can manipulate dimension properly to model waves etc, mathematically.
And I personally dont think that anything whatsoever exists at all aside
from dimension and waveforms which propagate in it.

"JM Albuquerque" wrote in message
...
:
: "Rex" escreveu na mensagem
: ups.com...
:
: They say time is what the clock measures and time is ...
:
:
: Time is very relative.

Absolute NONSENSE.

On Fri, 24 Aug 2007 16:19:37 -0700, Rex wrote:

But i've been continued puzzled about
what time really is.

It is obviously none of your ****ing business. Get
yourself a job and **** off.

--

"che kas dAde budat namAyandegi
ke az ghowle mellat mozakhraf begi"

- Hadi Khorsandi