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What is Time?

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<< I still think they can only observe the effects of quarks, rather than actually seeing individual quarks. They have to exist in a neutral colour state, and I think it is theoretically impossible to get one on it's own. Various quarks were discovered at different times, which does suggest that the effects of individual quarks can be detected separately, but the particle itself hasn't been seen. >>



True, we have never seen a quark, just the path it leaves behind.



flood5: we agree =)
 
i think that time is a dimension. you are in the dimension but the rate of it is determined through velocity throughout the universe. some studies have shown that while flying against the rotation of the earth, time actually slows down. Einstein theorized that if you traveled the speed of light you would either be at a stand still or that you would actually travel back in time.

my theory is that the universe is a sphere that actually rotates around a center just as everything else does and that if you travel the speed of light with the rotation of the universe you will speed up the rate of time and if you travel the speed of light against the spin of the universe at the very edge of the universe you will actually stop time. you will come to a stand still in time at which nothing happens. by the way this explanation works it would mean that the very edge of the universe rotates at light speed.

my theories are not credible though because i have not finished high school physics, just another 4 months to go 🙂

[edit]took out 1 sentence, guess which one? 😀[/edit]
 
Einstein did indeed show that time slows down as velocity increases, but it's nothing to do with direction of travel. I believe the effect is measurable using very accurate clocks even after a concorde journey round the earth. The time difference shown by each clock is either millionths or possibly billionths of a second, but it still shows that time has passed very slightly slower onboard the moving plane than it has on the earth.

I can't be bothered to look it up now, but I think Einstein's theory says that everything travels through the Universe at a specific rate. For an object stationary in space, it moves through time to maintain this constant velocity. At light speed, all the the motion of an object is spatial and hence it will cease moving through time. In this sense time is relative, and the particle is still moving through 'our' time at light speed relative to us.
 


<< im scared >>


Congrats.. Welcom to Anandtech forums!

NOw.. I read from "How to build a time machine" by Paul Davis about travalling into the futuer and stuff. He was explaning that ... a pair of twins age 12. one goes off in a space ship and zooms off earth at near light speed for 2 years return trip. During the trip, at near light speed, the twin that travelled aged 2 years to become 14, but when she returned, she finds that her sister (the other twin) is aged at 20. This is due to time which expands or contracts. After Paul Davis explained this, he said that some people find this rather paradoxial as the story could be thought of as - the twin who remained on earth was moving away ffrom the other, in this case, the twin on earth should be the one who finds out that her sister is older. Paul Davis said that this is not possible as it was the first twin that fired the rockets and moved away. However, motion is relative isn't it? so either way you think about it, bothe are correct?
 
I've heard the same thing written in a number of books and always been confused by that particular paradox - glad I'm not the only one who finds it odd! The example I heard was even more paradoxical though since the twins were put in deep space equipped with rocket packs. That way their motion can only be compared relative to each other. Then which one ages? Still supposedly the one who fires the jet pack, but I've got no idea how that really works.
 

Better dont ask what time is for "real"
keep in mind, physicians discover principles that describe nature - not vice versa.
Of course you can use these priciples to explain phenomenons like thunder or radiation,
but theres nothing more real and nothing more true than nature itself.
For now we know time can be stretched or clinched. Until we find more,
time is the ting that lets you remember.
be the real thing 😎
 
Time, time... Its like a rhythmic ryme ryme.....

Time is just something for use to measure the rising and setting of the sun. Sun dials???? What whould time be on mars??? Well some genius would figure out its rotational spin and then try to use our system of time, but that would not work.... Because the Sun rise and the sun set would be different then on earth. So my idea is time is just something humans invented. Just like the wheel or car. Do you think the dinasours cared what time it was??? In a sense yes.... but maybe that is why they went bye bye. Ok this is getting strange. Maybe if they could tell time they would of had some idea when that great big boulder was going to get to earth??? Kind of a stupid thought, I know....

 
Why does everyone always say time is another dimension? when I was young the catch frase answer to the question "what is time?" was always "it's the fourth dimension". I thought dimensions were defined by the number of right angles perpendicular to one another. First dimension = line. Second dimension = right angle (now you have area). Third dimension = right angle to the second dimension (right angle). now you have volume. Fourth dimension = right angle to the third dimesion (can't visualize this one but I'm told it can be demonstrated/proven mathematically. And so on.

On a side note I pondered the meaning of time one night when I was about 7 years old. My thought process went something like: It takes an hour to go to grandmas house. If we drive faster it takes less time, if we drive farther it takes more time. Bingo!! Time is jsut the relationship between speed and distance. and if nothing moved or changed there would be no time, we'd be stuck in a moment, frozen in time. And time is not constant as rate and distance can vary so time is relative to your position in the universe (in relation to everything else, time passes faster in some places than in others but will always seem constant to you since your not moving that fast through the universe). Ah but now I'm rambling.

point is why can't time be nothing more than a way to catagorize change. the past is the state things WERE in. The present is the state things are in. And the future is the state thing will be in. OK, start tearing apart my over simplistic logic!
 


<< point is why can't time be nothing more than a way to catagorize change. the past is the state things WERE in. The present is the state things are in. And the future is the state thing will be in. OK, start tearing apart my over simplistic logic! >>


How about some Quantum Mechanics?

'Time', or more accurately said, what we perceive as 'change' is likely not to be 'fluent'. The universe offers a nearly infinite number of events, yet these are connected in 'frames', like a movie appears to display movement, even though it are just indvidual frames we're watching.

It's for this reason that some people have suggested that the universe is event-symmetric, i.e. it doesn't matter when a certain event happens. One can take a collection of events from one place in someone's 'timeline' and insert it in another location, after which things would still make perfect sense to that person.

Of course, this means that the 'direction' of 'time' doesn't matter. The universe has only a preferred direction, and we, together with other creatures and stuff are trapped in this linear 'flow' of time.
 


<< Einstein did indeed show that time slows down as velocity increases, but it's nothing to do with direction of travel. I believe the effect is measurable using very accurate clocks even after a concorde journey round the earth. The time difference shown by each clock is either millionths or possibly billionths of a second, but it still shows that time has passed very slightly slower onboard the moving plane than it has on the earth.

I can't be bothered to look it up now, but I think Einstein's theory says that everything travels through the Universe at a specific rate. For an object stationary in space, it moves through time to maintain this constant velocity. At light speed, all the the motion of an object is spatial and hence it will cease moving through time. In this sense time is relative, and the particle is still moving through 'our' time at light speed relative to us. >>



that is his theory, Einstein thinks that time is relative to velocity itself. on the other hand i believe that time relates to your velocity with respect to the rest of the universe. Einstein's theory is sort of like breaking the sound barrier, at one point in velocity you will stop hearing sound completely not based on direction at all. my theory is like flying around the world at a high speed to have the sun up forever until you stop but instead of basing it on whether you are the same spot on earth (relative to distance from earth and sun not taking into acount the spin of earth or orbit of earth) i base it on your point in the universe. i think that if you are can remain at the exact same spot in the universe, time will not move for you.

if you think about it, it can make sense
 


<< I've heard the same thing written in a number of books and always been confused by that particular paradox - glad I'm not the only one who finds it odd! The example I heard was even more paradoxical though since the twins were put in deep space equipped with rocket packs. That way their motion can only be compared relative to each other. Then which one ages? Still supposedly the one who fires the jet pack, but I've got no idea how that really works. >>



The only logical way I've seen this problem solved is by saying that the one that ages more slowly is the one that feels an acceleration and a deceleration. Otherwise if one could instantaneously travel at near-light speeds without being accelerated, there would be no way to tell which one would age.

-Ice
 
Could some one point me to a good artical about lightspeed? Or just answer a few questions I have.
1. If you were moving at light speed, you are still traveling through time but your time is slower than the time of lets say the poeple on earth. My question is that sence you are still moving through time doesnt there have to be a point there time and some speed faster than light intersect. Were there is no time. And could you put someone in that state, and use it like a time traveling device? (forward only of course).
2. Just a general explication why light speed is so important.
3. Someone said that a clock on a jet going past the speed of sound would be slightly slower. So wouldnt the clock on a space station be the same way? A space station is moving much faster than that plane.

On the topic of my final question it gives me an idea. When I get old I am just going to go into orbit of a planet with a really high gravity so that time would slow down. And I will be able to see all the advancements of our race.
 
Just seeing your post got me thinking about some things... i remeber hearing/reading that photons have momentum but no mass, and i thought how could that be (Momentum=massxvelocity). And then i looked at E=mc2, and saw it was basically energy=massxvelocity, or the same equation momentum has. Does that explain why photons have momentum but no mass?
 
Photons have no rest mass. Once moving though I think they can in ways be considered to have a mass, after all can't light be bent by gravity - in fact wasn't that one of the predictions of general relativity and used to prove the theory (some expedition was sent out to observe a particular distortion during a solar eclipse).

I don't think it's possible to actually travel at light speed. Given a constant force accelerating you, the acceleration would be asymptotic to light speed. You instead of accelerating further would start to gain mass instead. The effects aren't noticeable by humans until speeds significant compared with light speed are reached. Not sure what speed the ISS moves at, but the time dilation should be measureable but not noticeable by the occupants (they wouldn't be able to watch the people on Earth moving about in fast motion)
 


<< I don't think it's possible to actually travel at light speed. >>

That assumption is correct. Once v approaches c, m becomes oo (infinite).
 


<< That assumption is correct. Once v approaches c, m becomes oo (infinite). >>



That's also true, since you need to put an infinite amount of energy into the object to accelerate it towards c. That's because the faster you go, the more mass you have. Therefore you input even more enery to accelerate faster, which will again cause the increase in mass.
 
But why would mass slow you down if you had the perfect place where nothing acted on the object. I guess there would still be its ever growing gravity but that should not mess it up.
 
The mass doesn't slow you down, but it does cause 2 problems:

1) You need to put in more energy to increase the speed further
2) You need to put in the energy to create this mass

Since the mass approaches infinity as the velocity approaches c, you would require an infinite amount of energy to accelerate to light speed.
 


<< I think Einstein's theory says that everything travels through the Universe at a specific rate. For an object stationary in space, it moves through time to maintain this constant velocity >>


One of Einsteins postulates that there is no way to measure/detect absolute motion. 😛 Hence, there cannoot be an object that is truly in the rest frame of the universe. Objects can only be at rest in their own rest frame relative to other things.



<< Why does everyone always say time is another dimension? when I was young the catch frase answer to the question "what is time?" was always "it's the fourth dimension". I thought dimensions were defined by the number of right angles perpendicular to one another >>


Actually Einstein more or less said that.
Newtonian physics defines the universe in three dimensions (x,y,z) and time being something all observers agree on (haha).
Einstein said you need one more dimension (x,y,z,ct) this is known as the space-time 4-vector. This means that time varies with the observer. If you take the dot product of this vector, and modify it a little, you get (x^2)+(y^2)+(z^2)-((ct)^2) Set this equal to A. Suppose A represents a rocket ship flying through space. A will be the same for all observers regarless of their reference frame (this includes velocity).



<< Other "scietists" have claimed that the big mysterious explosion out in siberia (forgot its name, started with t I think) was caused by a chunk of antimatter slamming into the earth which isnt as far fetched as you think. >>


actually, it is :-] the explosion would have happened in the atmosphere. the antimater doesnt have to hit the ground - it doesnt really care waht it is as long as its matter.



<< Einstein thinks that time is relative to velocity itself. on the other hand i believe that time relates to your velocity with respect to the rest of the universe >>


assuming that you mean the rest of the universe to be the true rest frame goes against einstein's postulate "One of Einsteins postulates that there is no way to measure/detect absolute motion"
What hes basically sayin is that motion is always relative, there is no way to measure your "true" speed relative to space. This makes sense since even you were somehow able to find the true rest frame of space, if you were to travel fast enough, you and an observer in the rest frame would disagee on your speed due to time dialation and lenth contraction
 


<< Photons have no rest mass. Once moving though I think they can in ways be considered to have a mass, after all can't light be bent by gravity >>


when you move really really fast, classical newtonian physics no longer applies, you have to start using different formulas to compensate for time dialation and length contraction
relativistic momentum is (mass)*(c)*(gamma)(v/c)
c = speed of light; v = velocity; gamma = 1/sqrt(1-(v/c)^2)
when v reaches c, gamma becomes infinite, but mass remains at zero, so a photons relativistic momentum is infinite. (this'll drive the math people crazy 😉, but it works out)
 


<< I don't think it's possible to actually travel at light speed. >>


Relativistic energy is defined as: (rest energy + kinetic energy)
E = m(c^2) + m(c^2)(gamma-1)
as you approach the speed of light (see my previous post for gamma), gamma approaches infinity, and as does energy (kinetic and total). This means you'd have to put an inifinite amount of energy into the acceleration.
 


<< Just seeing your post got me thinking about some things... i remeber hearing/reading that photons have momentum but no mass, and i thought how could that be (Momentum=massxvelocity). And then i looked at E=mc2, and saw it was basically energy=massxvelocity, or the same equation momentum has. Does that explain why photons have momentum but no mass?. >>


photons have no rest energy :-]
 
So just how much energy are we talking about? Infinite can me a lot of things. A friend of mine basically stated that it was impossible to go the speed of light for even a relatively small particle because it would take roughly all the energy of the known universe to get it there. Anyone that can give me a # to grasp?
 


<< Einstein did indeed show that time slows down as velocity increases, but it's nothing to do with direction of travel. I believe the effect is measurable using very accurate clocks even after a concorde journey round the earth. The time difference shown by each clock is either millionths or possibly billionths of a second, but it still shows that time has passed very slightly slower onboard the moving plane than it has on the earth. >>


time dialation and length contraction becomes more dramatic at higher speeds. The atomic clocks on the planes showed a slight difference.
Muons created in the upper atmosphere reach the surface of the earth all the time. They decay *very* rapidly (2.2 microseconds as i recall). Moving at .92c relative to an observer on earth, they dont cover enough distance to reach the surface of the earth in that 2.2microseconds (using newtonian physics). However, applying some einstein, we see why the muon is able to reach teh surface to the earth.
Suppose an observer on earth has a clock and there is a clock strapped to the muon.
From the observer standing on the earth, they will see the muon age about 2.5 times more slowly and see its clock tick about 2.5 times more slowly.
From the viewpoint of the muon, it will see the distance to the earth contract by 2.5 times and will not notice a time dialation. It will think its clock is accurate and will live 2.2microseconds (according to its own time), but the distance it had to travel in that time shortened.

Remember that in realativity, all observers have to agree on the facts (for example, that the muon in fact did reach earth). However, explations due to different reference frames can differ.

Also, in a particle accelerator, you can make something like a muon travel at .9999c and have it live for hundreds of times as long as it usually does when its not moving so fast.
 


<< So just how much energy are we talking about? Infinite can me a lot of things. A friend of mine basically stated that it was impossible to go the speed of light for even a relatively small particle because it would take roughly all the energy of the known universe to get it there. Anyone that can give me a # to grasp? >>


how much energy?
Relativistic energy is defined as: (rest energy + kinetic energy)
E = m(c^2) + m(c^2)(gamma-1)
gamma = 1/sqrt(1-(v/c)^2)

so, the rest energy, we dont have to apply, just m(c^2)(gamma-1)
suppose you want to go .99c
then you have gamma = 1/sqrt(1-(.99)^2) = ~7
so youd have to put in 6 times the rest energy to get it to go .99c, which is a whole lot!
make it .999c and you have to put in 21 times the rest energy
make it .9999c and you have to put in 69 times the rest energy
make it .99999c and you have to put in 222 times the rest energy
make it .999999c and you have to put in 706 times the rest energy
make it .9999999c and you have to put in 2235 times the rest energy

And this is assuming 100% efficency and no friction!
This is why its only practical to make a single molecule travel at .99c or so, and those particle accelerators use a whole lot of power to do it.

aw crap... just realized i left out a power of 2 in all my posts
 
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