# The Naked Scientists Forum

### Author Topic: Why does time slow down at speed?  (Read 18676 times)

#### yor_on

• Naked Science Forum GOD!
• Posts: 11652
• (Ah, yes:) *a table is always good to hide under*
##### Why does time slow down at speed?
« Reply #25 on: 18/05/2011 00:28:29 »
It's that citation you used actually, I presumed it was your point of view too?

"(?)He said that they never observed any discrepancy between relativistic mass, inertial mass and gravitational mass(?) He was answering to the question of the difference between gravitational mass and relativistic mass. (ahh?)... Each proton is perceiving the other proton's mass increase as a true mass and they are much smaller in size..

The only way I can make sense of such a statement should be in its 'interaction', measuring the 'energy' released. If it is meant as a proof of 'relativistic mass', and so the protons 'potential energy' to be one and the same at all times, they will need to prove it to be so without comparing versus 'interactions', as different 'interactions' will give you different answers. And so it comes back to being 'at rest' versus what you measure the 'relativistic energy' 'Potential energy', etc, against.

And there you only will find the invariant mass, as I see it, discussing uniform motion. The problem here is acceleration, it depends on how you look at that. Is a acceleration a definition of something that never begets 'instants' of uniform motion, or is it a 'jumping' from state to state?

In the first definition you have acceleration as something differing from the idea of QM where everything in some manner needs to be 'quanta', a discrepancy that here translates into motion as a 'smooth phenomena' not fitting QM. In the other definition you will find that you suddenly can translate any acceleration to something similar to 'the photoelectric effect' and 'black body radiation', meaning that all accelerations are equivalent to a infinite (? not really as we have 'c' but?) amount of 'uniform motions' jumping from one state to another as defined by our arrow of time.
« Last Edit: 18/05/2011 00:43:19 by yor_on »

#### CPT ArkAngel

• Hero Member
• Posts: 571
• Thanked: 3 times
##### Why does time slow down at speed?
« Reply #26 on: 18/05/2011 02:19:50 »
First, you have to accept that the relativistic mass is inertial mass and the proof of that is in all particles accelerators. Then, you have to accept the Equivalence Principle that says that Gravitational mass and Inertial mass are the same. At collision time, the 7500m0 for each proton is for the lab's observer frame, the 15000m0 is for 1 proton viewed from the other. Any measurement made within any unique inertial frame cannot differentiate relativistic, inertial and gravitational mass... That is the Equivalence Principle. We must agree on definitions first. We will all agree about that :)... You can only measure by interacting...
« Last Edit: 18/05/2011 02:34:13 by CPT ArkAngel »

#### yor_on

• Naked Science Forum GOD!
• Posts: 11652
• (Ah, yes:) *a table is always good to hide under*
##### Why does time slow down at speed?
« Reply #27 on: 18/05/2011 02:36:18 »
"the Equivalence Principle that says that Gravitational mass and Inertial mass are the same."

I don't dispute that gravity act as an acceleration? After all that is the essence of the Equivalence principle when it comes to accelerations and gravity. But where exactly did he state that relativistic mass is invariant?

As I remember it he never liked the idea of 'relativistic mass' himself? As for what made sense to me in that experiment, it was, as I said if you try to read it, that it had to be the 'measurements' aka interactions. And also that it was this way of defining relativistic mass as 'really, really, there' that sounded wrong to my ears. The fact is that for you to measure any existing real effects on a object moving, as defined against any other frame of reference, you will have to be 'at rest' with it. And there you will find no 'extra energy' in that moving object, no matter its velocity. That means that no 'atoms' in it will 'jiggle' due to its motion.

And that's why the definition of invariant mass makes a better sense to me.

==

Assuming moving in a vacuum, classically defined as having no resistance, creating no 'friction'. When it comes to accelerating, creating a gravity, the definition of a friction less vacuum becomes slightly weird, but as I see it, having to do with the room time getting 'compressed'.
==

Ask yourself, if a Lorentz contraction is real, is that equal to a compression?
If so, shouldn't the atoms in the Lorentz contracted ship heat up as they are compressed in the axis of the motion? And If you think that this is possible, how about the rest of the Lorentz contracted universe then? As seen from the ship? Also 'heated up'?
« Last Edit: 18/05/2011 02:52:59 by yor_on »

#### CPT ArkAngel

• Hero Member
• Posts: 571
• Thanked: 3 times
##### Why does time slow down at speed?
« Reply #28 on: 18/05/2011 03:20:25 »
Relativistic mass is not invariant, nor inertial mass or gravitational mass. Only rest mass is invariant. We don't have the same definitions...

For a proton having a relativistic mass of 7500m0 in the accelerator frame (corresponding to a fixed speed), the accelerator pushing the proton will perceived the proton as having an inertial mass of 7500m0.

Yes, i agree that invariant mass is more fundamental. If all matter is made of light, then relative movement of matter imply Relativity... :o)
« Last Edit: 18/05/2011 03:34:53 by CPT ArkAngel »

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Why does time slow down at speed?
« Reply #29 on: 18/05/2011 03:30:24 »
Ok, here's the points I've been trying to make in perhaps a simpler form:

1) If gravity is fully determined by mass alone, then you have to be in a reference frame where the mass is stationary.  In this case, the rest mass and relativistic mass are equal.

2) If your mass is moving, you cannot compute the gravitational curvature of space-time from mass alone--neither relativistic mass nor rest mass tells the whole story.  In this case, you need to compute the stress-energy tensor, which has 16 components (10 of which are unique).  You need to obviously know a lot more than just a single number for mass to compute the gravitational field here.

My original point was to argue against MikeS's claim that higher relativistic mass equals more time dilation, since things aren't so simple as that.  If you believe that relativistic mass alone is enough to determine the gravitational effects, then you believe that fast moving particles spontaneously form black holes for some observers and not others--which is false.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11652
• (Ah, yes:) *a table is always good to hide under*
##### Why does time slow down at speed?
« Reply #30 on: 18/05/2011 04:00:10 »
Yeah JP, I was wondering when we would introduce the stress energy tensor :) That one is about the room time geometry to me and as such perfectly reasonable, then again, I'm slightly weird :)

You're perfectly correct.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11652
• (Ah, yes:) *a table is always good to hide under*
##### Why does time slow down at speed?
« Reply #31 on: 18/05/2011 09:41:14 »
CPT, you have a point in that it will take more energy the faster something moves, and if you like you can translate that energy drain into moving a greater (invariant) mass at a slower velocity, begetting the same numbers. It's a equivalence of sorts I agree, but it's you pushing, or dragging, that object expending energy in a accelerator. In itself it does not change any invariant mass, at least not due to any motion in a perfect vacuum.

The reason I think so is that all particles accelerated in a vacuum otherwise, at some state as I see it,should start to glow, melt into some weird plasma, whatever :) And as they don't?
==

It's not really such a great analogue thinking of it again as those particles constantly are interacting with a electromagnetic field, getting up to speed. But I still think I'm right there.
« Last Edit: 18/05/2011 09:58:48 by yor_on »

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Why does time slow down at speed?
« Reply #32 on: 19/05/2011 08:39:56 »
The point I was getting around to making has since been covered but I will mention it anyway.  As I see it there is only energy and mass in the universe.  One kind of energy can be converted into another so from the point of view of E=mc2 only energy needs to de considered.  Likewise with mass, there is rest mass and all of the other kinds.  But the other kinds are simply rest mass plus energy of one kind or another.  Even rest mass has gravitational (kinetic) energy.  So from E=mc2 we only need to consider energy and mass.

JP
Going back to the space-ship.
As it accelerates up to the speed of light it experiences no passage of time and its length has diminished to zero (?).  It would seem that the space-ship has possibly lost two of the four dimensions of space time.  If this were the case then its mass would only have to compress two spacial dimensions out of existence to become a singularity not the usual four of space time.  Just a thought.

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Why does time slow down at speed?
« Reply #33 on: 19/05/2011 08:42:01 »

JP
Going back to the space-ship.
As it accelerates up to the speed of light it experiences no passage of time and its length has diminished to zero (?).  It would seem that the space-ship has possibly lost two of the four dimensions of space time.  If this were the case then its mass would only have to compress two spacial dimensions out of existence to become a singularity not the usual four of space time.  Just a thought.

Fortunately it can't reach light speed, so we don't have to worry about it becoming a singularity in any dimensions.

#### marksesl

• First timers
• Posts: 1
##### Re: Why does time slow down at speed?
« Reply #34 on: 11/03/2013 17:53:20 »

Think of two mirrors at rest relative yourself, then let a light-corn bounce between them. As it does you will find the path that light-corn to take being a straight path, back and forth, a little like a pendulum.

Now let the mirrors move with you staying at earth, it won't matter if you look at them while accelerating, or after as they start to 'coast' in space. From your point of view the light-corn suddenly will move slower, due to you finding that light-corn having a longer path between the mirrors, that as it has to traverse more 'space' as the mirrors it bounce between constantly moves away from you. Also you will find the path it takes to be  a diagonal one as it 'tags' after the mirrors in a zigzag motion relative you, being still.

First of all, what is a "light-corn"?

Now, even though I see the light moving diagonally, thus farther, I would also the the overall movement of the mirrors.  That movement would have to be added to the movement across (from mirror to mirror), and would fully explain how a longer diagonal distance could be traversed in the SAME amount of time.  So, why would there be any need for time dilation?

Imagine two children tossing a ball back and forth in a car.  If the car begins to move, the ball will have to travel a longer distance, even much longer since the car will be moving quite fast compared to the side to side velocity of the ball.  If I only took into consideration the distance the ball was traveling diagonally, I would have to experience an immense amount of time dilation.  Of course, that is not the case at all because I would also have to take into account the forward speed of the car that would be added to the speed of the ball which would fully account for why the ball can travel a long diagonal distance in the same time as the short distance it traveled while the car was stationary.  So, no time dilation.  So, I'm still confused.  Why does time slow down with relative speed.

#### Bill S

• Neilep Level Member
• Posts: 1797
• Thanked: 11 times
##### Re: Why does time slow down at speed?
« Reply #35 on: 11/03/2013 19:07:14 »
Quote
Why does time slow down with relative speed.

My understanding is that in the case of the ball in the car; when the car is moving an outside observer would measure the speed of the ball to be greater because of the addition of speeds.

On the other hand an outside observer would measure the speed of light as being the same when the mirrors were moving as when they were stationary.  Thus the situation is quite different.

#### yor_on

• Naked Science Forum GOD!
• Posts: 11652
• (Ah, yes:) *a table is always good to hide under*
##### Re: Why does time slow down at speed?
« Reply #36 on: 11/03/2013 23:13:57 »
The answer isn't that straightforward. First you have to accept the validity of 'frames of reference', being comparisons between different points in space and time. Then you have to accept the idea of all inertially moving observers being equivalent. Then you have to introduce a absolute frame of reference, relative all those 'inertial observers' (uniform motion, or being in 'free falls', acting on you without resistance) called 'c'. Then you need to notice that 'c' only can be 'c' relative such a 'inertial observer', and that any acceleration will distort the path giving it a different value according to the original definition. And I'm most certainly missing important points, but they should do for now I hope?

One description that catches the idea is someone bouncing a ball in a railroad wagon. To the guy inside the ball goes straight down and up. To the guy standing at the embankment, watching the train go past him, you can imagine the balls path to then form a V. If we assume the train to have a 'uniform speed' we can pretend that it is a inertially moving object from the point of the guy standing at the side watching it. This is not a very good example but it works to show you the idea behind it. That depending on observer we will see a different motion, and also define it as taking a different time. I have a link describing it better than I ever will :) Special Theory of Relativity: Clocks and Rods.  SR is a space without 'gravity', just as a 'free fall' can be seen as, ignoring tidal forces as the earth rotating.

#### The Naked Scientists Forum

##### Re: Why does time slow down at speed?
« Reply #36 on: 11/03/2013 23:13:57 »