When thinking of cycles and myths, one cannot pass the idea of Kronos or Kali. That brought me to form some questions about the nature of time.

Three definitions for time:

a) Time is a measure of the change. Change is a result of the forces.
b) Time can be understood as a consciousness of history, present and future, which emerge from capable of memorizing.
c) Time is relative as per Einstein.

Time as a relative yet real "thing" is confucing (I'm probably not only one in the world :-). Everything on universum seems to be in a movement. Atoms, cells, inner human organs are in constant change, earth rotates and orbits around sun. Sun orbits and rotates on galaxy, galaxy rotates and orbits or expands or moves on space. Maybe a huge unisystem (contra ecosystem) of galaxies are still moving as a group. Now because there is so much movement and forces, how come one can say, that time slows in moving objects or that it is something real, something more than change and movement and concept of human mind?

It is told, that time is relative to gravity. What is the exact particle one measures and compares to the gravity then? Say our head is 72 inches above the ground. Time is slower on head than on toes. Does this mean that aging is different for different parts of the body, or that just atoms gets older, or that earth rotation compared to the sun is different for head and toes and so forth up to higher scale?

Primitive natural way to understand time is to see the change of days and years. Think of time traveller who takes a trip in speed of light years and comes back and sees everything is 5 years older that his clock says. Of course trip itself brings up plenty of paradoxes in physical sense, but what I'm thinking is if travellers aging process got slower, or did planets and sun, maybe whole galaxy change their speed relative to traveller and people on earth? Or was it only the atomic clock that slowed down?

I'm not sure if I'm able to to describe the problem I'm facing when trying to understand, what is really meant with special relativity theory. I quess its really something to do on atomic or quantum level and huge speeds, which brings me to question, if there is any real world usage with the theory?

www.dailymail.co.uk/sciencetech/article-...
www.timephysics.com/what-causes-time.htm...
en.wikipedia.org/wiki/Motion_%28physics%...

Real world usage for the theory?  Indeed.  One of the daily ones is satnav location systems, whose signals have to be adjusted for time dilation in order to provide you with high accuracy.

One major riddle about time is the nature of Now - no Now is found in any of our physics.  I'm also unconvinced by the claim commonly met that the arrow of time is caused by entropy.

Checking Wikipedia, I notice that examples in physics in which, it used to be said, t=0 have tended to be modified so that it doesn't.  The speed of a tunneling particle is one.  However the resolution of entangled particles is arguably still that way, though explained so as not to offend the Einsteinian rule that information can't be transfered faster than c.

The scientific questions in the OP can be answered easily enough.

But the truth is, the smartest physicists is the world are still rather baffled by time.  There are those who think that as theoretical physics progresses (if it progresses!) time will prove not to be a fundamental property of physical laws at all. Well, maybe.

Also, it may be that it is we ourselves who greatly overplay the significance of time.  This is because dealing with "time" is absolutely critical to consciousness.  It is true, there is no "now" (or, rather, to conscious beings "now" is meaningless); everything we perceive is a succession of states which musty be processed by the brain into something coherent. Even something so simple as hearing a word is not simple at all; it is really a rapid succession of changes in frequency and amplitude which manifest themselves as changes in position of the microscopic hairs in the ear. The brain must make sense of these, somehow store each successive state in short-term memory until the entire word is spoken, then compare it with patterns in its long-term memory to make sense of it. Without being able to process these continual changes in perceptual states, there would be no consciousness.

This topic is still on my interest, I'm constructing some more material. But since the word consciousness is raised here, which is very appropriate, I'm willing to start a new thread about it. Maybe it will produce some extra thoughts about time as well. Thanks for your replies already. :)

Apr 17, 2012 -- 4:07PM, markom wrote:

......../.........how come one can say, that time slows in moving objects or that it is something real, something more than change and movement and concept of human mind?

It is proven every day in particle accelerators that time slows down in relation to acceleration, and slows down more the closer one gets to the speed of light.

It is told, that time is relative to gravity. What is the exact particle one measures and compares to the gravity then? Say our head is 72 inches above the ground. Time is slower on head than on toes. Does this mean that aging is different for different parts of the body, or that just atoms gets older, or that earth rotation compared to the sun is different for head and toes and so forth up to higher scale?

We don't notice the relativity effects of time until we get close to the speed of light. Why is time relative to gravity? It took Einstein about ten more years to realize why this is the case (between the 1905 Special Theory and the 1915 General Relativity). He realized that acceleration and gravity were equivalent (I think this is where he said he had the most marvelous thought of his life). Therefore, being in a gravitational field is the same thing as accelerating (therefore, being in space away from earth gravity is getting closer to the speed of a photon, and thus time slows down). I read recently that physicists can now measure relativity effects of heights of differences of one foot.  

Primitive natural way to understand time is to see the change of days and years. Think of time traveller who takes a trip in speed of light years and comes back and sees everything is 5 years older that his clock says. Of course trip itself brings up plenty of paradoxes in physical sense, but what I'm thinking is if travellers aging process got slower, or did planets and sun, maybe whole galaxy change their speed relative to traveller and people on earth? Or was it only the atomic clock that slowed down?

This is the twin paradox. The twin that stayed home does indeed age. Again, this is proven every day in particle accelerators.

I'm not sure if I'm able to to describe the problem I'm facing when trying to understand, what is really meant with special relativity theory. I quess its really something to do on atomic or quantum level and huge speeds, which brings me to question, if there is any real world usage with the theory?

I don't know how to make relativity simple. You just have to keep digging it out, reading different physicists explaining it. I'm essentially worthless as a mathematician, but relativity can be pretty-well explained in words. Einstein made the assumption (from many people measuring it) that the speed of light is constant. If the speed of light is constant, then space and time must be relative to the speed of light. He realized that space and time are somehow mixed, there is not space separated from time, but we have a space-time continuum. If you were on a spacecraft and got close to the speed of light, your 25 ft. spacecraft, to you, would continue to be 25 ft. But to someone on earth, the spacecraft would be shorter than 25 ft. (because, moving faster, it becomes shorter). 

As a teenager Einstein wondered what it would be like to ride upon a beam of light. From this he eventually came to Relativity. Consider this. Look at a clock with a second hand. A photon coming off that clock at 1:00:00 travels 186,000 miles before the clock hits 1:01:00. Einstein came to understand Relativity by considering that photon (of course, a particle of light wasn't yet called a photon. At that point (most) everybody considered light a wave. It was in another 1905 paper, the photo-electric effect, that Einstein showed that light could act as a particle). 

sdp