Is it plausible that time sometimes does change speeds, but we can't prove it because the clock, our only means for measuring time, also speeds up and slows down?

Einstien's Theory of Relativity Applies here. His theory states that people willo disagree on time dependent on their relative speed. For example when a clock is taken in a rocket into space it is a few seconds out, because of the speed it travelled at.

It's a common thought experiment in physics/cosmology to imagine time "stopping" for one million, billion years or more (okay, I know that doesn't make sense--for if time is stopped how can millions of years pass? Duh! But just humor me, here :-)

During that time-stoppage, all the molecules, atoms, particles of matter, and strings of energy will "freeze." When time "resumes" the state of all matter will continue from exactly what it was before the "freeze." We would never be aware of time having stopped or changed "speeds."

Also, our bodies are made out of the same stuff (atoms) that clocks are, so there is no scientific way we could even test for such a time stoppage.

This bloke has a pretty good cosmology tutorial ( http://www.astro.ucla.edu/~wright/intro.html ) and ( http://www.astro.ucla.edu/~wright/cosmo_01.htm ).

Hope I'm not breaking a rule. I gave this answer to another question but it seems to be more appropriate for this one.

There is no such thing as time. Time is nothing more than a conceptual way of comparing one physical motion with another. All common methods of gauging time (the hour, the minute, the calendar, etc.) are nothing more than divisions of the length of time it takes for the earth to rotate around it's axis or revolve around the sun.

There is no way to prove that the time it takes for the earth to rotate once on it's axis is constant unless you assume that the time it takes for the hour hand on your clock to rotate around it's access 24 times is also constant. What if we say that we don't know if either of them are constant? Then we would need a third motion to compare both those motions with and would have to assume that the third motion is constant and on, and on.

Now think or the entire universe as a clock with every single atom's relative position moving in relation to every other atom. In order to go back in time we would have to return to a point at which every atom was at a given position and state of existence and the entire universe would need ot be restored to that state. This would include the atomic state of your brain and everyone else's as well, which would include the memories stored within. Since everything is back to the state it was in at that given "time" and all memeory states in the universe are also restored to that given state, even if we could go back in time, no one would be aware of it, since there would be no "memory" of the "future" that had presumably "happened" anywhere in existence.

This is why time travel only works for science fiction and even then it causes incredible theoretical debate that is never resolved. So far every theory has had flaws. Except Einstein's theory of relativity. Which is exactly what my theory is based on.

Of course, you could always put insant coffee in the microwave.

Steven Wright tried it once and almost went back in time.

Isn't time a human concept. Time is there, solely because we say it is there?

time is infinite,there is no beginning an there is no end,time will always exist regardless weather the earth or therefore any planet exist or not.