I would like to start an intelligent discussion on how one measures time in true space. Going on the assumption that time is measure by orbital movements it would seem that once you left the orbit of Earth time would cease to exist as we know it. Just to let you know, I’m not a scientist.

The way we measure time is relative to the spin of the earth giving us our day and the orbit of the earth around the sun, giving us our year. But everything in the universe is in motion and time, so to speak, marches on. Someone from another planet around another star will measure time relative to their conditions but it will still be time passing. Time won't stop when we leave the boundaries of our solar system but the units used will vary for every other intelligent civilization in the universe. We will still age but possibly at different rates relative to earth time.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Time and time measure are 2 different things. Time doesn't cease to exist simply because you don't have a clock. Space probes use clocks (atomic clocks in the case of GPS satellites).

If you want to define a calendar in interstellar space, you can use pulsars.

This looks like a very interesting thread! I too am not a scientist - which is why I occasionally indulge a bad mood by thinking that time is just something invented to annoy me :) but I don't often have bad moods - so thank you! I would like to think they would have a more me-friendly clock on board if I was travelling through space, but I would put up with a pulsar if that was the majority view :) I look forward to learning more :)

We don't actually speak of time in the Universe, but of spacetime.

E=MC² infers that time is relative to the observer.

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rOZZ
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E=MC^2 does not define the relativity of time. It defines the relationship between Mass and Energy. Look at "Time Dilation" to see that there are two notions of time especially when one is moving rapidly relative to an observer. The equation is due to Einstein and time dilation comes from the Lorentz transformations.

There is the local time of the traveler and observer time as well.

Time is an illusion which we order events in our lives. It can be measured as the elapsed interval between events.

E=MC^2 does not define the relativity of time. It defines the relationship between Mass and Energy. Look at "Time Dilation" to see that there are two notions of time especially when one is moving rapidly relative to an observer. The equation is due to Einstein and time dilation comes from the Lorentz transformations.

There is the local time of the traveler and observer time as well.

Time is an illusion which we order events in our lives. It can be measured as the elapsed interval between events.

Time was and always will be hard to measure. I like Stephen Hawking's view on the definition of Time, a lot!

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rOZZ
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These are some very interesting and nice responses so far. We all know that there are different ways a person measures time relative to the planet that he or she is on and how long it takes to orbit the sun. Lets take Jupiter for a contrast. A year on Jupiter is equal to 11.9 Earth years. A day on Jupiter is equal to 9.8 Earth hours. The Pioneer 10 spacecraft was launch by NASA in March 1972 and passed by Jupiter in Dec. 1973. A total time of 1 year and 9 months Earth time. But say I was living on Jupiter, then it would have taken the P-10 eleven plus years to reach me. Now lets say that I was on the P-10 and my darn watch broke and I couldn’t communicate with Earth or Jupiter. How would I measure the passage of time? Yo mentions pulsars and atomic clocks but how would that work? You have to be able to see a pulsar won’t you? And an atomic clock must be set to some standard?

I know that time is an arbitrary unit of measurement, and I know that I’m overthinking this. But it does boggle my mind to know that in a thousand years this is going to be a real problem to all of our space faring friends. Ha!

These are some very interesting and nice responses so far. We all know that there are different ways a person measures time relative to the planet that he or she is on and how long it takes to orbit the sun. Lets take Jupiter for a contrast. A year on Jupiter is equal to 11.9 Earth years. A day on Jupiter is equal to 9.8 Earth hours. The Pioneer 10 spacecraft was launch by NASA in March 1972 and passed by Jupiter in Dec. 1973. A total time of 1 year and 9 months Earth time. But say I was living on Jupiter, then it would have taken the P-10 eleven plus years to reach me. Now lets say that I was on the P-10 and my darn watch broke and I couldn’t communicate with Earth or Jupiter. How would I measure the passage of time? Yo mentions pulsars and atomic clocks but how would that work? You have to be able to see a pulsar won’t you? And an atomic clock must be set to some standard?

I know that time is an arbitrary unit of measurement, and I know that I’m overthinking this. But it does boggle my mind to know that in a thousand years this is going to be a real problem to all of our space faring friends. Ha!

I still have a problem with it now :)... and as for getting my head round the fact that a day on Venus is longer than a year... (did I get that the right way round - oh dear - if I didn't I'm going to look really stoooopid :))

Maybe there is no such thing as time, only change. And that time is just a human construct to help us quantify the rate of change and to coordinate our activities with such a system of measurement. Such a system has been essential to calculations in practical and scientific applications, though. But, what if there is no such thing as time??? Just like how a number of sociologists and anthropologists acknowledge that there's no such thing as races in humans, just a convenient and arbitrarily made up pigeon-holing system.

Maybe there is no such thing as time, only change. And that time is just a human construct to help us quantify the rate of change and to coordinate our activities with such a system of measurement. Such a system has been essential to calculations in practical and scientific applications, though. But, what if there is no such thing as time??? Just like how a number of sociologists and anthropologists acknowledge that there's no such thing as races in humans, just a convenient and arbitrarily made up pigeon-holing system.

Albert Einstein said: "People like us who believe in physics know that the distinction between the past, the present and the future is only a stubbornly persistent illusion"

In an attempt to prove my alarm clock is indeed one such stubbornly persistent illusion, I had a quick delve into the subject to brush up on what I'd forgotten and found this:

The fact that the present which gives us the most real feel of time cannot be measured while the inaccessible past and future can be measured as durations strongly suggests that the way we perceive time (present-ism or the block universe view) is an illusion.

In the block universe, past, present and future exist together superimposed in different dimensions. This view of time suggests that dinosaurs are still alive and roaming the earth in other time dimensions; so are multiple copies of us and the whole universe. This view is reinforced by Einstein’s General Relativity (GR) in which time extends as the fourth dimension from the past to the future. Lack of simultaneity in Einstein's SR and an interpretation of the Lorentz transformation equation also promote this view.

Theory of Relativity predicted slowing of time with motion and gravity. These predictions were soon confirmed in particle accelerators and gravity experiments. But, if there is a block universe, why do particles and masses with slower time not disappear into the past? In gravitational fields space is clearly continuous between areas of slower and faster time. Black holes with their intense gravity that bring time to a screeching halt do not disappear from our present into the past. Slowing of time without sliding into the past or the future suggests that time is a process and not a dimension. This may be a significant point against the block universe view of time when taken together with other aspects of time and given that it derives its support from Lorentz transformation equations which have never been proven experimentally.

Which simply proves to me that thinking about time messes with my head :) but is a lot of fun when it doesn't involve alarm clocks (unless I can believe I am already up when I'm not).

Anyway - back to the topic - would that mean that we would measure time by the distance we've travelled from earth if we were travelling in space? We'd probably have to chuck speed into our calculations too I suppose...

Anyway - back to the topic - would that mean that we would measure time by the distance we've travelled from earth if we were travelling in space? We'd probably have to chuck speed into our calculations too I suppose...

A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.

Planck Time is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel in a vacuum.

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rOZZ
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A light year is still linked to earth measure, ie. the year. On a planet with a longer year their definition of a light year would be longer.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

A light year is still linked to earth measure, ie. the year. On a planet with a longer year their definition of a light year would be longer.

As long as the end result is equal. It is a specific distance, whether defined in miles, kilometers, light years, or any other unit of measure.

Steve

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A light year is still linked to earth measure, ie. the year. On a planet with a longer year their definition of a light year would be longer.

As long as the end result is equal. It is a specific distance, whether defined in miles, kilometers, light years, or any other unit of measure.

Steve

My point is that a light year is a unit of distance relative to the 365 days it takes earth to travel around the sun and that distance is only relevant here on earth.

Someone from a planet orbiting another star would measure a light year in terms relative to his/her planets orbital period and it would be an extreme coincidence if it were the same as earth's. So our measure of a LY is only relevant on earth.

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Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

A light year is still linked to earth measure, ie. the year. On a planet with a longer year their definition of a light year would be longer.

As long as the end result is equal. It is a specific distance, whether defined in miles, kilometers, light years, or any other unit of measure.

Steve

My point is that a light year is a unit of distance relative to the 365 days it takes earth to travel around the sun and that distance is only relevant here on earth.

Someone from a planet orbiting another star would measure a light year in terms relative to his/her planets orbital period and it would be an extreme coincidence if it were the same as earth's. So our measure of a LY is only relevant on earth.

Relevant to us, to be able to grasp distances in the Universe. That's why we have the parsec and the AU as well.

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rOZZ
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E=MC^2 does not define the relativity of time. It defines the relationship between Mass and Energy. Look at "Time Dilation" to see that there are two notions of time especially when one is moving rapidly relative to an observer. The equation is due to Einstein and time dilation comes from the Lorentz transformations.

There is the local time of the traveler and observer time as well.

Time is an illusion which we order events in our lives. It can be measured as the elapsed interval between events.

“For those of us who believe in physics,” Einstein once wrote to a friend, “this separation between past, present and future is only an illusion.”

From this, we can come to only one conclusion. Time is an invention of man so that he/she isn't confused by things all happening at once.

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How do you measure time in space?

Firstly, how can we 'measure' that which we believe is 'time'?


At the moment, the best we can do is to mark the passage of distance and assume that some 'time has passed' whilst traveling that distance.

The iconic visible example of that is the swing of the pendulum of a clock.


Note that the pendulum experiences movement. We assume that there is a passing (or 'flow') of time along with that... We have no direct detection or measure of that which we call 'time'...

Keep searchin',
Martin

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I am still not happy with Martins definition of time. He seems to insist that it has always has something to do with motion...

See: Constants of Nature

Note that all the constants, and from those everything about our universe, all depend singularly upon the assumed speed of light and what we have determined to be the Plank length.

You yourself have described the idea of the "light year" that we use as an astronomical measure.

I can leave a book on a table, and start a stopwatch beside it. Some interval later I can stop the stopwatch and remove the book.

Relative to your view they appear to be stationary. Relative to your view there are parts in the stopwatch that are in motion and increment a counting mechanism as a certain point is passed in the motion of the timepiece mechanism. We count time as a number of times a particular point is repeatedly passed by some part of some timepiece mechanism.

We have no idea whether the 'flow of time' that is experienced is smoothly continuous, progresses in steps (quantized), or indeed is constant at all!

We already have physical confirmation in experiments here on earth and across the cosmos that the 'flow of time' is relative to your frame of reference...

There appears to be no "absolute time" for our universe.

In neither case did the book or the stopwatch move, only the hands of it. If an electronic stopwatch, then just the digits would be changing. What the stopwatch shows is the elapsed period between me leaving the book there and me retrieving it.

That is what you experience for your frame of reference.

The units that we choose to measure the elapse between the two events are arbitrary. For want of a better word we use time to describe this elapse between the two events.

Exactly so. We use moving mechanisms (that have some part that moves some distance in some way) to 'mark' a sequence of events/moments for that mechanism.

We also know that a device to record these durations which we call time, will record slightly differently whether it is motion itself or not. Clocks on the ISS will run slightly slower than on earth because of relativistic effects of it's motion relative to earth and time dilation, predicted by Einstein in 1905.

Indeed so. Just one clue that we might see/experience something different that is dependent upon our frame of reference. That also suggests there is something more than just our Newton 'classical' view of our every-day understanding of what is the 3-dimensions in which we move and live and experience the abstraction that we call "time".

Time is time is time. It is the same stuff everywhere, this stuff just elapses slower in some circumstances from the respect of different observers. It's like a runner in a 100 metres race, it's the same runner no matter how fast they complete the event.

If the runners are subatomic, then even though they may run along the same track, they can take what appears to us to be an infinity of routes to appear to complete the race in very different ways...

What we call 'sub-atomic particles' are likely not 'particles' at all even though they can have particle-like behavior. However, there is a lot more to their story... And thinking beyond "3-dimensions + time" gives some tantalizing results to explain our universe...


See and follow?: Einstein's Intuition - Quantum Space Theory



Keep searchin',
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
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...Time will be time will be time will be time whether you like it or not!

Especially when it comes to the very old cry of:

Last Orders!

Time Gentlemen Please!


(And the units for time for that period are highly subjective and very much non-constant... ;-) )


:-P

Cheers,
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)