Time, Relativity thing

Originally posted by xmaddness
Okay prepare yourself for some heavy concepts.

Step 1) The difference between relativity and special relativity.

Einstein had 2 theories of relativity. The first theory term just General Theory of Relativity is a theory that involces mass and light and proposed that matter causes space to curve. The famous equation E=Mc^2 was the final outcome of this theory. E= enery, M= mass, c=the constant of the speed of light.

What this equation dictates is that as mass approaches the speed of light, it will turn towards pure energy rather than mass. It also predicts that travel faster than the speed of light is impossible...

This equation says no such thing, nor has it ever. E=mc^2 tells us the amount of energy contained within a certain amount of mass, that is, it says that there is no difference between energy and mass.

From the field equations of special relativity we know that the mass of an object that is traveling at high velocity will increase to infinity at c, when measured by a motionless observer. It will by no means "turn toward pure energy."

Originally posted by xmaddness
Why? As I stated before, as mass (or a ship) approaches the speed of light, the mass will also increase. The amount of power to keep this object going also increases. (because you are going faster and your mass is increasing until you don't have enough power to push this growing mass faster). The theory states that once the mass reaches the speed of light, it then turns into pure energy (or elctomagnetic wave particles i.e. light)

"Pure energy" again? I suggest you google "relativity field equations" to see the equation (I assure you, E=mc^2 is not it) that actually allows one to calculate this effect of what used to be called "relativistic mass," and drop the "pure energy" thing. It don't happen.

Originally posted by xmaddness
Now on to the Special theory of relativity.

The special theory of relativity adds one more thing to the equation, and was actually never finished by Einstein. (He later called it one of his life's biggest failures)

What did he try to add into it?

Gravity

Wrong again. Maybe you should read a bio of Einstein or something.
There is technically only one theory of relativity. The General Theory of Relativity actually contains the Special Theory as a special case.

It was the General Theory that included gravity, and it was certainly not a failure, not according to Einstein, and not according to anyone else.
Einstein's "biggest failure" (if I remember correctly) was the addition of his "cosmological constant" into his cosmology. This constant was applied to cancel out the universe's expansion he saw in his equations, and he inserted it because he considered the idea of expansion to be ludicrous. A few years afterward, the very expansion he had predicted (and denied) was discovered.

Originally posted by xmaddness
If I were to build a space ship, and say goodbye to you and fly off to the outer rim (event horizon) of a black hole, my time relative to you would increase. ie one year for me would be multiple years for you. The greater gravity is for me, the slower time will go for me relative to the you in a less gravity situation. This has actually been proven by the Hafele and Keating Experiment. A good explanation can be found here, and info on the experiment can be found here.

This gravitational time dialtion is what many refer to as the "Time machine" syndrome in which one can travel into the future.

You need not fly into any massive gravitational field for this time dilation to occur. It is a consequence of the relative differences in our velocities and the fact that it is you that has changed his velocity from mine, and not vice-versa.

It is true however that a massive gravitational field affects time in the same way that high velocities do. I believe the idea of travel into the past had to do with the geometry of spacetime near a black hole. Spacetime would be warped around to form a loop on itself, allowing for travel into the past. It has recently been found that the geometry of a black hole will not allow for this effect to occur, though that is not true of other, non-spherical supermassive objects (if any exist.)

Harte
edit - fix quotes

[edit on 8/6/2005 by Harte]

It has been a while since I have really delved into this subject. I apologize if some of my recollection of the theories is flawed. I have alot of other thories based upon Einstein's theory from other authors such as Kip Thorne and Stephen Hawking.

I think I may be pulling some thories of them into Einsteins theories.

I do aologize.

xmad

My take on it in layman's terms is that the light you see from a distant star actually left that star a long time ago. Had you the ability to travel faster towards that light than the light is travelling towards you you would theoretically be travelling backwards in time. However, your time relative to the light would remain ticking, you can't go back beyond your starting point and yet relative to the light of the star you would be speeding towards its origin even though time had elapsed since your onset of the voyage which is in effect still time ticking above the countdown and not below.
Having said that, the relativity comes into the perspective of the starting point of your journey and not your destination. This is time dilation so in theory it would be possible to break that time barrier relative to the light but not to yourself. In this I don't think that it would be possible to in essence, turn around and get back before you left.

IMO if we were to go FTL we would be entering a new realm since we are only speaking of visible light and as such are limiting our view. (no pun intended) Nothing we see can go faster than light doesn't mean that things unseen can't go faster. Is this SR, I don't know, as far as that goes, theories always work until proven wrong. ... but consider going into a black hole faster than the gravity is pulling you in... you would negate those forces that would be pulling you apart.
Are these gravity waves that can be manipulated (as in gravity assist)and as such does this open the door to time travel? Who knows... I'd wonder how it could even be explored since going in doesn't mean you are coming out although perhaps this is the big crunch and ultimately would lead to a big bang... maybe even the spark that reverses the trend in which case its a highly dubious undertaking at best given our current understanding.

btw, I'd like to commend you all on your inquisitive minds and level of intellect. It has me thinking, exploring and learning.

Some of you talk as if time is a physical object that can be manipulated. I don't understand how time is anything other than from point a to point b. Anyone care to explain or pinpoint certain post?

Frosty lol you do get to the heart of the matter don't you.
To me, Time is a factor in calculating speed= distance/time. It isn't a tangible etched in stone concept since our time is merely an illusion created by man. It does help when trying to predict or explain.
As time travel goes, it seems like something that can be touched or manipulated that answers or clarifies how it can be done (theoretically) and yet the equation of speed=distance/time is as delusional as distance or speed is.
What is distance is relative to our understanding of point A to point B (as in our size)and speed is the duration (time taken) between. Really, time is in the minds of the beholders.
By any other name it would still be the sum of our understanding a duration between two fixed points.
I don't know that I've explained it all that well other than the best description I've heard, time is only relevant to which side of the bathroom door you are on.
Taking this a step further, over time, wasted time, free time all can be factors in determining a duration that as such can be measured. Without a concept of duration we wouldn't have any time on our hands. (sorry pun intended)

I guess to sum this up, time is everything (age) and yet time is nothing. (a concept)

My favorite definition for time has always been "the distance between two events."

It's marginally acceptable, but the concept holds. Time is not a constant like regular life makes us believe, but rather a very mutable concept. It's just another dimension, nothing special.

Originally posted by Frosty
Some of you talk as if time is a physical object that can be manipulated. I don't understand how time is anything other than from point a to point b. Anyone care to explain or pinpoint certain post?

Special relativity predicts time dilation, which says a traveler experiencing velocity will "move forward" in time with respect to a stationary observer that remains in the reference frame from which the moving observer has originated.

This is a direct consequence of Einstein accepting as an axiom the constancy of the speed of light.

The thinking goes like this.

First, consider you are on a train moving at 5 mph and your brother is standing on the ground watching the train go by.

Standing in the aisle, you toss a baseball in the direction of the train’s movement (forward) at 5 mph relative to you. You see the ball as moving at 5 mph.

Outside the train, your brother would see the ball moving at 5mph (speed of your throw) + 5mph (speed of the train) = 10mph. This is apparent and logical.

Now:

A traveler is in a spaceship moving very near the speed of light (say c-1mph) with a clock on the interior wall and is being observed by a stationary observer on the planet he left from, who also has a similar clock on his wall.

The traveler shines a flashlight in the direction of his motion.

The traveler measures the speed of his flashlight beam to be c (naturally.)

Intuitively you would think that the stationary observer, looking in through the spaceship window, would measure the speed of the light beam to be c (speed of the beam)+c-1 (speed of the ship)=2c-1mph, relative to him. In fact, the observer measures the speed of the beam to be c, which is less than 2c-1. How do we account for the speed measurement taken by the observer being less than it should be?

There are only two ways that this can be possible:

Speed is measured by taking the distance the beam traveled (to the front wall of the spaceship, presumably) and dividing that distance by the time the beam took to reach the wall (distance/time, or d/t). If the distance to the wall, as seen by the stationary observer, is less than the distance seen by the traveler, then the observers’ calculation of speed will be less than if this did not occur, since the distance is the numerator in the fraction d/t.

Similarly, if the time measurement taken by the observer is greater than the time measurement taken by the traveler, then the speed calculated by the observer will be less, since time is the denominator in the fraction d/t.

Since the speed of the beam must be measured to be c, regardless of who measures it, then Special Relativity says that either the time taken by the beam to reach the wall or the distance traveled by the beam to the wall (or both) must be different for the two observers. In fact, it is both the time and the distance that are different. The stationary observer measures the time taken by the beam to be more than that measured by the traveler, so time for the observer is “moving” more quickly relative to the time measured by the traveler (this is the “time dilation” you have heard of in relativity.) Also, the observer measures the distance to the wall to be less than the same distance as measured by the traveler, so length in the direction of travel has decreased for the observer relative to the distance as measured by the traveler (this is the “contraction of length” you may or may not have heard of in relativity.)

Many know of the atomic clock experiments that have been used to verify the accuracy of Einstein’s field equations (the equations that calculate the effect of time dilation based on relative velocity between the original stationary reference frame and the new moving reference frame.) These experiments did in fact confirm the accuracy of these equations. But many people are not aware that time dilation can be, and has been, confirmed in the laboratory as well.

In particle accelerators, particles are traveling at speeds approaching c. The properties of particles that are the result of collisions in accelerators are known. Specifically, the expected life span of some of the more short-lived particles that decay into other particles rather quickly (in milliseconds, if not nanoseconds.) Given the known life span and the known velocity of these particles, it is easy to determine how far they will travel before they decay into different particles.

In every case, these particles are observed to travel much farther than predicted before they decay. And in each case, the period of extended life for such particles exactly matches the expected lifespan extension that can be attributed to the quantity of time dilation the particle should be experiencing per Einstein.

In fact, were this not true of these particles, there are many which we would know very little about, we wouldn’t have had time to observe them long enough to make any deductions about them, they would have decayed so swiftly. So it can be said that particle physicists depend on relativity.

Harte


[edit on 8/9/2005 by Harte]

Originally posted by Harte
Special relativity predicts time dilation, which says a traveler experiencing velocity will "move forward" in time with respect to a stationary observer that remains in the reference frame from which the moving observer has originated.

This seems to defeat the purpose of relativity by stating two observers in relative reference frames experience different actions, based soley on speed.

Outside the train, your brother would see the ball moving at 5mph (speed of your throw) + 5mph (speed of the train) = 10mph. This is apparent and logical.

I don't see this happening unless the ball is thrown at anything other than toward the rear of the train at an angle and not perpendicular.

Intuitively you would think that the stationary observer, looking in through the spaceship window, would measure the speed of the light beam to be c (speed of the beam)+c-1 (speed of the ship)=2c-1mph, relative to him. In fact, the observer measures the speed of the beam to be c, which is less than 2c-1. How do we account for the speed measurement taken by the observer being less than it should be?

If I were standing on a carpet traveling 500 mph and shot a bullet out of a gun going 500 mph, I don't think the bullet will hit an object infront of the carpet at 1000 mph. Though maybe it could. Maybe you have velocity mixed with acceleration.

In particle accelerators, particles are traveling at speeds approaching c.

This is missleading as anything with an increasing acceleration is approaching the speed of light.

Originally posted by Frosty

Originally posted by Harte
Special relativity predicts time dilation, which says a traveler experiencing velocity will "move forward" in time with respect to a stationary observer that remains in the reference frame from which the moving observer has originated.

This seems to defeat the purpose of relativity by stating two observers in relative reference frames experience different actions, based soley on speed.

What are you referring to when you say "the purpose of relativity"?

Outside the train, your brother would see the ball moving at 5mph (speed of your throw) + 5mph (speed of the train) = 10mph. This is apparent and logical.

Originally posted by Frosty
I don't see this happening unless the ball is thrown at anything other than toward the rear of the train at an angle and not perpendicular.

A person on a train moving at 5 mph throws a ball inside the train car, up the aisle, in the direction of travel of the train. The ball is thrown at a speed of 5 mph according to the thrower. A person standing outside the train observes the train's velocity to be 5 mph, and sees the ball moving forward at 10mph (train speed + ball speed.)

Intuitively you would think that the stationary observer, looking in through the spaceship window, would measure the speed of the light beam to be c (speed of the beam)+c-1 (speed of the ship)=2c-1mph, relative to him. In fact, the observer measures the speed of the beam to be c, which is less than 2c-1. How do we account for the speed measurement taken by the observer being less than it should be?

Originally posted by FrostyIf I were standing on a carpet traveling 500 mph and shot a bullet out of a gun going 500 mph, I don't think the bullet will hit an object infront of the carpet at 1000 mph. Though maybe it could. Maybe you have velocity mixed with acceleration.

Maybe, but I don't think so. If your bullet is moving at 500mph before you fire your gun, if the gun is pointed in the direction of your travel and the velocity of the bullet relative to the gun barrel is 500mph after you pull the trigger, then the velocity of the bullet relative to the carpet is 500mph, but relative to a person not on the carpet, the bullet is traveling at 1,000mph as it exits the guun barrel.

If you fired the bullet at someone behind you that was not moving with your carpet, the bullet would never hit them (500mph - 500mph = carpet speed - bullet speed = 0).

In particle accelerators, particles are traveling at speeds approaching c.

Originally posted by FrostyThis is missleading as anything with an increasing acceleration is approaching the speed of light.

Semantics. Technically, anything with acceleration (increasing or not) is approaching whatever speed you wish to name, unless it has already passed the particular speed you had in mind.

Accelerated particles are moving at speeds approaching the speed of light. These particles have speeds that are near enough to the speed of light for relativistic effects to be observable.

The equation for time dilation is t' = t*sqrt[1-(v/c)^2]
t' = time measured by the traveler
t = time measured by the stationary observer
v = velocity of the traveler
c = speed of light
You can see from this that a fairly high speed must be reached before t' varies significantly from t.

Harte

Originally posted by CloudlessKnight
There is no such thing as time...

You're right in a sense ... in fact, as I start to learn more about physics I start to wonder about our notions of time ... it becomes mathematically convenient at some point due to gauging to consider time not as a separate isolated thing, but as merely yet another dimension.

But, the funny thing, is that when we "look" at things, taking a step back, we really need some sort of stopwatch to obtain our data points.

I've been reading Max Planck's Lectures on Physics that he gave at Columbia. They are an excellent and concise introduction to these fundamentals.

What the problem is, is that our measurement technology is very limited. We cannot measure the "fastest" events, so we treat time as a 4th dimension ... but this is sort of a fudge factor.

What Planck mentions which I think is interesting, is the need to abstract our reasoning away from our measurement devices ... and it might indeed appear that not having a traditional metric of time is the right path towards this all encompassing objective.

In fact, I'm just thinking right now that a more accurate concept would be the RATE of time passage ... we know certain atoms decay at certain rates for example (cesium atomic clock standard) and we also know that photons propagate at various rates through differing materials.

The difficulty in relativity is that the mass of the object can change due to it's energy / velocity. This points out alot of difficulties in how we define our low level world ... most of which are originally derived due to our measurement techniques used in classical physics.

Perhaps then if having a fixed time metric seems too crude, it would make more sense to track the rate and acceleration of time.