Originally posted by Dolphin55 Someone earlier mentioned time dilation, which I think is really helpful in trying to explain what time is.
Nice post.
Well, it may be helpful in a way, but unhelpful in others! It is the source of much of my confusion about what time is.
The answer to the question is that time is a measure relative to the observer. And this goes down to the heart of my confusion. If time is "something" which is not simply an abstract concept conjured by our perceptions of the word, then how can it be a measure of something relative to an observer? And, perhaps the real question, what is it a measure of?
Originally posted by AThousandYoung Time dilation means that the local rate of entropy change will vary with velocity, that's all.
How do you reconcile your view that time is a measure of how much entropy the universe has gained since the Bang (an absolute measure) with time dilation (time is relative to the observer)?
Originally posted by Palynka How do you reconcile your view that time is a measure of how much entropy the universe has gained since the Bang (an absolute measure) with time dilation (time is relative to the observer)?
I define absolute time as the amount of entropy the universe has increased as a whole. The local time is how much entropy has increased locally. All the local times in the universe make the absolute time. When an object moves very quickly, it's modified contribution to the total entropy is accounted for with relativistic equations.
I'm half making this up as I go along.
Time being relative to the observer means that the change in local entropy observed per unit of absolute time is less at high velocities, and thus there is less aging, less thinking, less everything.
Gosh I wish I knew what entropy meant. i have no idea what you are talking about.
The poor chap wants to know what time is.
Time is a measurement of a period. We use clocks with a timespan that reasonably matches the rotation of the Earth. All of our timeframes are related to the Earths rotation period, the Earth going round the Sun, the Moon going round the Earth. All the rest of the chit chat is confusing matters. Time is a useful measurement of a period.
Originally posted by Dolphin55 Gosh I wish I knew what entropy meant. i have no idea what you are talking about.
The poor chap wants to know what time is.
Time is a measurement of a period. We use clocks with a timespan that reasonably matches the rotation of the Earth. All of our timeframes are related to the Earths rotation period, the Earth going round the Sun, the Moon going rou ...[text shortened]... h. All the rest of the chit chat is confusing matters. Time is a useful measurement of a period.
You're right, of course, but there are more hidden facts about time.
we can compare the dimension time with the the dimension length. You can go from your home, go in a circle and come home again. But you cannot start now, go in a time circle and return to now again. You can only go forward in time.
Why this restraint on time, but not in length? The answer lies in the deeper aspect of time. There is a reason. The thing is to find the answer.
A bad answer is always: "Because it is that way!" or "There is no answer, because if it was, some nobel prize winner would already have found it out."
I wish I'd chosen to be a physicist! But I do agree with whoever said the speed of light is not constant; it is constant in a vacuum but changes as it passes through different media. This is also why a prism works to disperse the colours within light. Longer wave length light (red) refract less and shorter wavelength refract more - hence the colour split. How much a medium refracts light is called refractive index. Similar phenomena can be seen with a stick in a bucket of water; where the stick looks bent.
I'm speculating massively now, but because of prismatic effect, could I assume the speed of light is dependent on its electromagnetic energy (wavelength) as a function of the medium it's travelling through (density etc). Could I then suggest (by a cosmic leap) that time could have the same properties - i.e. be a function of the local cosmic mass and the density of space fabric? I.e. the more stuff there is in closer proximity the bigger the effect of time. So we have "refractive index -- why not "time index"?
This is sort of what I was suggesting in my earlier post.
Originally posted by FabianFnas You're right, of course, but there are more hidden facts about time.
we can compare the dimension time with the the dimension length. You can go from your home, go in a circle and come home again. But you cannot start now, go in a time circle and return to now again. You can only go forward in time.
Why this restraint on time, but not in length? The ...[text shortened]... is no answer, because if it was, some nobel prize winner would already have found it out."
Yes, this is closer to my preferred view but, as you say, there are deeper aspects missing.
Originally posted by divegeester I wish I'd chosen to be a physicist! But I do agree with whoever said the speed of light is not constant; it is constant in a vacuum but changes as it passes through different media. This is also why a prism works to disperse the colours within light. Longer wave length light (red) refract less and shorter wavelength refract more - hence the colour ...[text shortened]... ndex -- why not "time index"?
This is sort of what I was suggesting in my earlier post.
Thats a nice idea. time does slow down as you approach the event horizon of a back hole - perhaps your 'refractive' idea has some merit!
Regarding time being a measurement of a 'period' ... that doesnt get us very far! A period of what? What is the essence of time?
In special relativity, an "event" in spacetime (you can see this as simply space and time added together) is represented using 4 dimensions; the three spatial dimensions and time represented in terms of the speed of light times time ct (this means the unit of time is effectively represented in terms of a distance, since m/s * s = m). However, this does not mean that time is "just another distance", since there are differences with respect to time in the mathematical formulation of special relativity (I won't go into the details).
In special relativity it is assumed that events that are causally related must have a timelike seperation, this means the time between the events must obey c²t² > r², where r is the spatial seperation between events. In other words, any kind of "force" must travel at a maximum speed of the speed of light, so there is no physical mechanism by which I or anything around me can influence anything on Brazil in an instant.
The part of spacetime which obeys c²t² < r² is called spacelike. This part has no influence on you, nor can you ever see or influence anything in it.
So what "is" time? Physicists are not really concerned with what "is", but with an empirical description of things we see around us, for which the concept of time seems to work, at least for now. Philosophically I am interested in the question, of course, and it could be that time is just an illusion, etc. etc. Matrix clichés.
As for how entropy fits in the relativity story, I cannot comment on that since I don't know enough about relativity.
Originally posted by divegeester I wish I'd chosen to be a physicist! But I do agree with whoever said the speed of light is not constant; it is constant in a vacuum but changes as it passes through different media. This is also why a prism works to disperse the colours within light. Longer wave length light (red) refract less and shorter wavelength refract more - hence the colour ...[text shortened]... ndex -- why not "time index"?
This is sort of what I was suggesting in my earlier post.
Well, there are two (well, more, but let's keep it simple) "speeds of light". There is the speed at which light happens to travel through an arbitrary medium, and there is the constant of nature c, which is the speed of light when traveling through vacuum and is commonly simply referred to as "the speed of light".
Originally posted by Dolphin55 Gosh I wish I knew what entropy meant. i have no idea what you are talking about.
The poor chap wants to know what time is.
Time is a measurement of a period. We use clocks with a timespan that reasonably matches the rotation of the Earth. All of our timeframes are related to the Earths rotation period, the Earth going round the Sun, the Moon going rou ...[text shortened]... h. All the rest of the chit chat is confusing matters. Time is a useful measurement of a period.
Entropy is a somewhat "mystical" property, because it both takes up an important place in physics and is hard to measure (there are no entropy-meters). In common language it's usually referred to as a measure of disorder (i.e. more entropy = more disorder), but that's a bit inaccurate. On a microscopic level, entropy is proportional to the logarithm of the amount of states the system can be in; S = k ln (omega), where omega is the number of states available to the system, S the entropy and k is an important constant of nature called Boltzmann's constant. So if you are regarding a system which can exist in 10 possible states (usually this figure is much higher of course), then the entropy is k * ln 10.
Originally posted by FabianFnas You're right, of course, but there are more hidden facts about time.
we can compare the dimension time with the the dimension length. You can go from your home, go in a circle and come home again. But you cannot start now, go in a time circle and return to now again. You can only go forward in time.
Why this restraint on time, but not in length? The ...[text shortened]... is no answer, because if it was, some nobel prize winner would already have found it out."
Well, in the spacetime formulation you are on a very different place in spacetime after you make that circle.
What really is time?
08 Jan '10 19:11
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