How do we know time exists?

I've always thought that time was merely a man-made idea, to keep track between events. But there are scientists (most famously, Einstein) that believe that time is a physical property, that can be "bent" by things like black holes.

My question is, what evidence is there that time is a real, physical thing, and not just an idea?

Originally posted by vivify
I've always thought that time was merely a man-made idea, to keep track between events. But there are scientists (most famously, Einstein) that believe that time is a physical property, that can be "bent" by things like black holes.

My question is, what evidence is there that time is a real, physical thing, and not just an idea?

Any series of events that do not happen all at once is proof enough. For example since you were born there have been a series of events in your life that did not happen simultaneously. Time spread them out.

Originally posted by joe beyser
Any series of events that do not happen all at once is proof enough. For example since you were born there have been a series of events in your life that did not happen simultaneously. Time spread them out.

the marks on the ruler do not make the reality

time is the marks on the ruler

the reality is matter and motion

just as a ruler is marked in miles (or meters), so time is marked in days and weeks and years

the years don't "exist"

Originally posted by vivify
I've always thought that time was merely a man-made idea, to keep track between events. But there are scientists (most famously, Einstein) that believe that time is a physical property, that can be "bent" by things like black holes.

My question is, what evidence is there that time is a real, physical thing, and not just an idea?

I believe Einstein, and I see time as a dimention not as a 'physical thing'. Do you see the spacial dimentions as man made ideas to keep track between objects / events? Do you see them as real, physical things?
As for time, existent or not, it is most definitely bent by gravity, and it is also relative. These are not beliefs. They are measurable effects that must be taken into account whenever accurate physics is required. A good example is GPS where both the speed of the satelites and the distance above the earth affect the timing of the signals.

Originally posted by twhitehead
I believe Einstein, and I see time as a dimention not as a 'physical thing'. Do you see the spacial dimentions as man made ideas to keep track between objects / events? Do you see them as real, physical things?
As for time, existent or not, it is most definitely bent by gravity, and it is also relative. These are not beliefs. They are measurable effects ...[text shortened]... the speed of the satelites and the distance above the earth affect the timing of the signals.

But isn't that just a matter of the signals being affected by distance/gravity, etc., rather than "time" being affected? For example, if I throw a baseball in outspace, it will move differently than on earth; but it's not "time" that's changed, just the enviornment.

As for dimensions, others like height and width, are indeed physical; these things are measurable, observable, and can interact with the environment. Time, not so much.

I'm not saying this to argue; I just really want a clear answer.

How does science "know" anything? What does it mean to "know" something?

We "know" time exists in the sense that some theories require time to exist and so far people have not succeeded in replacing said theories with timeless ones, if such a thing were possible.

Originally posted by vivify
But isn't that just a matter of the signals being affected by distance/gravity, etc., rather than "time" being affected?

No, it is most definitely not 'just a matter of the signals being affected'. The effects of relativity are very real and very much a case of time itself being effected. Every physical law that includes a time component is affected. So for example radioactive elements with a known half life will decay according to the time predicted by relativity, not by the time recorded on some universal clock. If a human were to be put in a near light speed spaceship and sent on a 100 year journey (from our perspective) they would not age 100 years. Every single aspect of the human body, chemistry, speed of thought, etc would all be affected. This is not 'just a matter of the signals being affected'.

As for dimensions, others like height and width, are indeed physical; these things are measurable, observable, and can interact with the environment.
How exactly do spacial dimensions 'interact with the environment'?

Time, not so much.
Why do you not think time is measurable or observable? As far as I know clocks do just that.

Every object has a physical position in time and space. Time is a bit different from space, but nevertheless is as real a dimension as the three spacial ones.

Originally posted by twhitehead
No, it is most definitely not 'just a matter of the signals being affected'. The effects of relativity are very real and very much a case of time itself being effected. Every physical law that includes a time component is affected. So for example radioactive elements with a known half life will decay according to the time predicted by relativity, not by t ...[text shortened]... tc would all be affected. This is not 'just a matter of the signals being affected'.[/quote]

Okay. This makes some sense.

How exactly do spacial dimensions 'interact with the environment'?

Well, the height of a tree can cause shade, be used to reach new areas, etc. But I think you point is that "height" or "width" in of itself, isn't a physical thing; but things that do have these dimensions are measurable (trees, mountains, etc.)

Why do you not think time is measurable or observable? As far as I know clocks do just that.

Clocks measure the man-made idea of time (hours, minutes, etc.), but we can't use clocks as evidence that time exists. It's kind of like collecting coins in Super Mario Bros. We can measure how many coins Mario is collecting, but we know those coins aren't actually real.

Every object has a physical position in time and space. Time is a bit different from space, but nevertheless is as real a dimension as the three spacial ones.

Yes, you've explained very well reasons that time isn't just an idea, as you explained in the first paragraph I quoted from you. I guess I just need to look into it more.

Originally posted by coquette
the marks on the ruler do not make the reality

time is the marks on the ruler

the reality is matter and motion

just as a ruler is marked in miles (or meters), so time is marked in days and weeks and years

the years don't "exist"

time is the marks on the ruler

if that is true (metaphorically), then time does exists! -it exists as the marks on 'the ruler'!

I have seen this very type logical error being made countless times by people that claim that doesn't exists; they say time is X AND say times does not exist when you cannot have it both ways.
If time is X (whatever X is) then that is what time is therefore time does exist because time exists as X!

But I haven't come across “ time is the marks on the ruler” before. Usually, and more typically, I have heard of time being dismissed as “just a series of events” and 'therefore' time doesn't exist.
But this is the same kind of logical flaw for if time literally is “just a series of events” and nothing more then, logically, that is what time is therefore time does exist because it exists as “just a series of events”!
(although I never thought it makes much sense to say time is just a series of events anyway because “a series of events” requires a 'series' but a 'series' implies 'before and after' which implies some kind of dimension and direction which surely, in this particular context, implies time! i.e. it implies the very thing as that 'time-denier' dismisses as nothing more than “just a series of events”! I don't think that's logically consistent)

Originally posted by vivify
Well, the height of a tree can cause shade, be used to reach new areas, etc. But I think you point is that "height" or "width" in of itself, isn't a physical thing; but things that do have these dimensions are measurable (trees, mountains, etc.)

And the exact amount of shade the tree provides is dependent on what time of day it is, something that was exploited very effectively with the sun dial.

Clocks measure the man-made idea of time (hours, minutes, etc.),
No, clocks measure time. The marks on the clocks are man made scales, just as the marks on a ruler are a man made scale (and may differ from culture to culture or system to system.) But a pendulum has a particular length, a particular mass, a particular volume and a particular period of swing. All these quantities are real physical quantities and the only thing man made about them is the units used to measure them.

It's kind of like collecting coins in Super Mario Bros. We can measure how many coins Mario is collecting, but we know those coins aren't actually real.
They may not really be coins, and may not even be physical objects, but they are real.

Originally posted by twhitehead
It's kind of like collecting coins in Super Mario Bros. We can measure how many coins Mario is collecting, but we know those coins aren't actually real.
They may not really be coins, and may not even be physical objects, but they are real.

Huh? Okay, I'm lost now.

But still, you opened my eyes to some things, and I'll just have to research it more. Thanks for taking the time.

Originally posted by vivify
Huh? Okay, I'm lost now.

Its a tough one really. Does information exist? Do you exist? Yes, I know you are made of atoms which make chemicals etc, but those are not the same atoms you had when you were a child. So are you a different you, or are you more than your atoms? And if you are more than your atoms, does that more exist?

There's only two kinds of situations where time does not exist:

1) Everything happens at once.
2) Nothing happens.

Originally posted by vivify
I've always thought that time was merely a man-made idea, to keep track between events. But there are scientists (most famously, Einstein) that believe that time is a physical property, that can be "bent" by things like black holes.

My question is, what evidence is there that time is a real, physical thing, and not just an idea?

Gravity. Seemingly.

Originally posted by Soothfast
There's only two kinds of situations where time does not exist:

1) Everything happens at once.
2) Nothing happens.

yes, in both those hypothetical situations, time would be totally meaningless.
There must be at the very least the possibility of something happening after something for time to mean something and arguably there must be actually something happening after something for time to mean something.