Question related to speed of light. (1 Viewer)

[Mike375]

As we know if you accelerate your time slows and if you could reach the speed of light then time for you would cease to move. To be hypothetical if you jump on a light beam then you would arrive at any place in the universe and from your perspective zero time would have elapsed. I think I have that right.

Astronauts have their atomic clocks running a couple of milliseconds slow.

Now to my question. What happens to time (from your perspective) when you de accelerate. For example the astronauts going to the moon accelerate out of earth orbit to escape velocity, about 26,000 mph and then shut down the engine in stage 3 of the Saturn V. From that point they de accelerate due to earth's gravity until about 30,000 mile from the moon when they are down to about 3,000 mph and then the moon's gravity has more influence than earth's gravity.

So what happens to their time during de acceleration.

 

[Minty]

It continues to be slower but at a reducing rate relative to their speed with relation to the speed of light.

 

[The_Doc_Man]

First, since we consider that we never stop moving relative to the frame of the universe (much less the galaxy, far less the solar system as a whole...)

All we do is resynchronize our time to that of the frames to which our relative velocity is zero. I don't think there is ever a time when we would go FASTER than the local frame.

Many theories of space-time do not even acknowledge that wall-clock time has any absolute meaning, only relative meaning. Therefore, to say that time stands still or moves slowly for you is a matter of some question. And I don't think it is EVER possible for something that isn't in the state of a wavicle to travel exactly at the speed of light, so you might never reach the "zero time flow" state. The practical reason is that to travel at the speed of light, the energy expenditure to accelerate to that speed rapidly becomes impractical 'cause you can't carry that much fuel.

 

[Mike375]

It continues to be slower but at a reducing rate relative to their speed with relation to the speed of light.

How can that be since we are de accelerating.

Just so we are on the same page here (and please correct me if I am wrong) this whole business of relativity and time distortion relates to a body or person accelerating. We all know if we leave earth in the space ship and accelerate to a high proportion of the speed of light and then return to earth perhaps a year has passed for the space ship passengers but 10 years has passed on earth.

It is not the same as two cars each doing 50 mph and are 100 miles apart but will meet in an hour or they go opposite ways then at 50 mph they will be 100 miles from each other after an hour.

We know we are doing about 1000 mph on the surface of the earth and about 65,000 mph around the sun and the solar system as a whole is moving but basis of time distortion is for a body or person to accelerate from their current position.

Thus if were doing the speed of light (OK..99.99999%) and started to de accelerate so after a year we reached 0 then would we have aged more than 1 year.

 

[Steve R.]

Read this thread: Does velocity or acceleration cause time dilation?

 

[speakers_86]

From their point of view, time is constant. Time dilation is only seen when you compare two different parties with different velocities (accelerations?). I think Minty was comparing their viewpoint to that of people on earth. edit-Yeah...accelerations, not velocities.

 

[Frothingslosh]

Thus if were doing the speed of light (OK..99.99999%) and started to de accelerate so after a year we reached 0 then would we have aged more than 1 year.

There's one problem. There's no such thing as 'de-acceleration'. Acceleration is nothing more than change in speed. The vector in which you accelerate is irrelevant.

As an example, let's say two trains are moving west at 100 kph. To observers on the ground, the trains are moving, but to observers on the trains, the GROUND is moving.

Now Train 1 starts to decelerate. An observer on the ground would see them decelerating, and an observer on train 1 would actually feel himself accelerating toward the back of the train. An observer on Train 2 would actually see Train 1 accelerating in the direction away from them, toward the direction from whence they came.

'Deceleration' includes an unstated vector component, and really just means 'acceleration directly opposite the direction of travel'. That's why you never see physicists talking about deceleration, only acceleration and vectors. That means you never de-accelerate, and thus there is never a point at which you age FASTER by changing your speed.

***

As to the whole speed of light thing, it's pretty complicated, but in a nutshell:

Objects in motion carry kinetic energy. The usual equation for that is this:

(KE is kinetic energy in newtons, m is mass in kg, and v is velocity in m/s)

Next up, acceleration is based on mass divided by force, or A = M/F, or as more commonly seen, F=ma (the force required is equal to the mass times the desired acceleration).

The final straw is that mass and energy are intraconvertible - they're two sides of the same thing and have a direct relationship explained by that most famous of equations E=mc^2.

Now the faster something moves, the more kinetic energy it holds, and that energy scales exponentially, not linearly. I don't know the actual formulas involved, but basically, once you have enough change in speed, the kinetic energy becomes a noticeable factor in the mass value specifically because there is an equivalency. The effect is that as you approach c, effective mass approaches infinity, and thus the effective force needed ALSO approaches infinity. To actually reach light speed, you would need infinite force, and thus infinite energy.

There are actually a whole series of equations that describe it in detail, but I'm afraid my calculus has twenty-five years of rust on it.

 

[NauticalGent]

y'all make my head hurt...

 

[Galaxiom]

... this whole business of relativity and time distortion relates to a body or person accelerating.

No. Relativistic effects are evident where observers are moving at constant speed. This is covered in Einstein's first theory of Relativity. It is called Special Relativity because it only covered the case of relative movement without acceleration.

Think of it this way. The speed of light isn't just the fastest speed in the Universe, its the only speed. When we are stationary, we are travelling though time at the speed of light. When we move though space we use some of the speed we normally use to travel through time. Consequently, although time seems to pass as normal for the traveller, the traveller's watch seems to be running slow when observed from the outside.

It took Einstein another decade to come to terms with General Relativity, the case where acceleration is also included. General Relativity showed that the effect of relativistic acceleration is indistinguishable from Gravitation.

We know we are doing about 1000 mph on the surface of the earth and about 65,000 mph around the sun and the solar system as a whole is moving but basis of time distortion is for a body or person to accelerate from their current position.

These speeds are trivial compared to light at nearly 300,000 km per second. Time dilation is calculated with Pythagoras's Theorem. Imaging the hypotenuse of the right angled triangle is the speed of light (remember the only speed there is). The speed through space and the speed though time relative to the speed of light will always be the sides of the triangle.

So even at galactic speeds like 30 km/sec (108,000 km/ 67,000 miles per hour) the time slows only a trivial amount.

At the other end of the spectrum and at the pinnacle of human ingenuity, my favourite is the Large Hadron Collider. It accelerates protons almost to the speed of light. This requires the kinetic energy of a Maglev train at over 200 km/hr being put into the equivalent of one teaspoon of hydrogen at room temperature and pressure. Much of that energy goes into increasing the mass of the protons.

 

[Mike375]

Galaxiom,

What is happening with time for the astronauts when stage 3 of the Saturn is shut down and they then begin to slow from 26,000 mph on their way to the moon.

"At the other end of the spectrum and at the pinnacle of human ingenuity, my favourite is the Large Hadron Collider. It accelerates protons almost to the speed of light. This requires the kinetic energy of a Maglev train at over 200 km/hr being put into the equivalent of one teaspoon of hydrogen at room temperature and pressure. Much of that energy goes into increasing the mass of the protons."

If the force that pushed the proton close to the speed of light is stopped and the proton slows down does its mass start to decrease and what happens with time for a little man who was riding on the proton.

 

[Frothingslosh]

Galaxiom,

What is happening with time for the astronauts when stage 3 of the Saturn is shut down and they then begin to slow from 26,000 mph on their way to the moon.

I'm not Galaxiom, but I can answer this:

You've heard 'objects in motion tend to stay in motion'? It's Newton's First Law, and what it means is that the velocity of an object - which incorporates both speed and direction of movement - does NOT change unless a force acts upon that object.

In the atmosphere, aircraft slow down due to air resistance. On the ground, vehicles tend to slow down bot from that and friction - friction between ball bearings and the axle, friction between the tires and the road, etc.

In space, in the absence of acting forces, an object will continue in a straight line at unchanging speed forever.

In the case of the Apollo missions, there's a tiny amount of air resistance for part of the trip, but its effect is fairly negligible. The real issue will be gravity - despite moving at higher than escape velocity, the module WILL be affected byEarth's gravity, which will still apply acceleration to the module pulling it back to Earth, and yes, from Earth's frame of reference, it means the module will 'slow down'. Once the module gets close enough to the Moon for ITS gravity to have a greater effect than Earth's, then you'll see the module accelerate toward the moon. The trick is making sure that the command module goes into orbit rather than into the Sea of Tranquility.

In all these cases, however, it's still acceleration. While being affected by it, the astronauts will see time pass by slightly more slowly than for an observer on Earth, but it would only be noticeable - eventually - to an atomic clock. We're talking thousandths of a percent slower.

"At the other end of the spectrum and at the pinnacle of human ingenuity, my favourite is the Large Hadron Collider. It accelerates protons almost to the speed of light. This requires the kinetic energy of a Maglev train at over 200 km/hr being put into the equivalent of one teaspoon of hydrogen at room temperature and pressure. Much of that energy goes into increasing the mass of the protons."

If the force that pushed the proton close to the speed of light is stopped and the proton slows down does its mass start to decrease and what happens with time for a little man who was riding on the proton.

The LHC fires the protons in a vacuum - the proton will NOT slow down just because the acceleration it was experiencing stopped. What's going to slow it down - rather dramatically - is the OTHER proton fired in the opposite direction when they impact head-on.

That said, yes, when the acceleration stops, so does the increase in mass. For the tiny little Slim Pickens riding that proton, time will appear normal. To us, because he's been accelerated to such higher an relative rate of speed and is in a completely different frame of reference, he will appear to be virtually in stasis.

 

[Frothingslosh]

Where I think you're having difficulty is that there is no such thing as 'at rest', nor is there a 'default' speed. Objects can be at rest relative to each other - our usual frame of reference is simpy 'at rest in regards to our surroundings' - but everything is always moving. Things don't naturally slow down; it always takes a force of some kind to change an object's velocity. People don't normally see that simply because we tend to take gravity and friction for granted.

 

[speakers_86]

Yup! Time dilation is always with regard to two parties in different frames of reference. If I get on a plane, time is normal to me, but if you looked at me from the ground, it would appear that I was slowed down just a tiny bit to you.

 

[Mike375]

Yup! Time dilation is always with regard to two parties in different frames of reference. If I get on a plane, time is normal to me, but if you looked at me from the ground, it would appear that I was slowed down just a tiny bit to you.

But isn't the time slow down for the person the plane "real'

It is my understanding if I can hop on a light beam and head to the
Alpha Centauri system then from the perspective of both earth and the people on a hypothetical earth like planet at Alpha Centauri 4 years will have passed. If a message had been sent from earth on 27/5/2012 that I would be jumping on the light beam on 27/5/2016 then the people at Alpha Centauri expect me to arrive on 27/5/2020 as do the people on earth.

However when I arrive my atomic clock shows no time has elapsed, the piece of ice on my plate has not melted etc. and etc. On my arrival the people at the Alpha Centauri send a message to earth saying I have arrived. I also intend spending 24 hours at the Alpha Centauri system doing a tour to see how things are out that way

So 24 hours after my arrival I jump on the light beam and when I arrive back at earth it will 28/5/2024 on earth and also at the Alpha Centauri system.

My face will look at if I have not shaved for 24 hours and my atomic clock will show 24 hours has elapsed.

If instead of going to the Alpha Centauri system I went to a planet that was 1000 light years from earth then it would be the same for me, that is, when I returned to earth my clock would only show 24 hours have passed and my face would be like not having shaved for 24 hours.

Is the above the case or am I wrong?

On the other hand if had been on a space ship that took a year to get to the speed of light then my clock would show far longer than 24 hours passing. However, when I returned to earth after my 24 hour stop over then many many years would have passed on earth.

 

[Frothingslosh]

Time is just as real regardless of whether you're on Earth, a world at Alpha Centauri, or travelling at c. Earth and Alpha Centauri are in virtually the same frame of reference (they don't quite have the same speed and vector), so they will basically experience time at the same rate. As you accelerated to light speed, however, you' will indeed experience a shorter duration, because yes, as far as we know, if you were to accelerate to light speed somehow, time would stop for you. So yes, if you traveled 4 light years at light speed, then on Earth and AC, 4 years would have elapsed, while for you no time would have elapsed. Same for your return trip.

And yes, if you traveled 1000 light years at light speed and then returned, 2000 years would have passed on earth, but the time you experienced would be limited to your time accelerating and your stay on the alien world.

As to your last question, it depends on the frame of reference. If it took a year on Earth for your ship to reach c, then for you it would have rather less than that - time dilation would become quite noticeable at maybe 0.6c. (Also, to someone on Earth, your acceleration would appear to slow as you approached light speed, and you would actually vanish from their frame of reference right as you reach c.

If you go be a subjective year - meaning that's what you experienced during acceleration - then the time on Earth would depend on the force of the engines. That's...more complicated.

There are actually some novels that get it basically right. The Honor Harrington series has to keep track of that due to how quickly the ships can accelerate, and the author regularly mentions that a trip may take 18 days by the universe's clocks, but only 13 by the ship's clocks.

Then there's an older novel called The Forever War, where time dilation is front and center - the entire story revolves around that.

 

[Mike375]

So the key point is I was accelerating.....taken to the extreme by jumping on the light beam......but whether jumping on the light beam or accelerating more gradually on the spaceship......the time for me has slowed down or in the case of jumping on the light beam the time stopped.

Now let's just use the spaceship for starters. Both the earth and my spaceship were separating like 2 cars.....but instead of each car doing 50 mph and hence being 100 miles apart in 1 hour the spaceship is like one car being standing still and the other car departing at 100 mph.

So to me it is accelerating that is the key. The rate of acceleration is only relevant from the point of view as to how long it takes to get to the velocity or how long (in our trip) we spend at the velocity.

So now I want to ask my original question again......

If a force causes us to de accelerate does time speed up for us and does our mass reduce. What happened to the Apollo astronauts when Stage 3 shot down at about 26,500 mph and they "slowed" to about 3000 mph when they were about 30,000 mile from the moon.

A second variation on the question. When stage 3 shut down they were in free fall. Let's say instead of just stage 3 just shutting down there were retro rockets fired that reduced their velocity from 26,000 mph to 0. Would time speed up for them and would their mass be reduced.

 

[speakers_86]

I feel like you're missing the point. We are discussing relativity. Time is relative. As far as I'm concerned, a watch on my wrist moves at a constant speed regardless of anything else. An external observer might argue and say my rate of time is different than his. Neither would be wrong, in fact, we are both right because time is relative.

 

[Mike375]

I feel like you're missing the point. We are discussing relativity. Time is relative. As far as I'm concerned, a watch on my wrist moves at a constant speed regardless of anything else. An external observer might argue and say my rate of time is different than his. Neither would be wrong, in fact, we are both right because time is relative.

But if I can jump on a light beam I can go to a planet a 100 years light years from us, spend 24 hours looking around and grab something to eat and then jump on the light beam and be back on earth only 24 hours older whereas you are dead and long gone when I arrive back on earth....

My atomic clock will show 24 hours have passed, during my tour and look around but your clock will show far far far more times has passed.

 

[Rabbie]

But if I can jump on a light beam I can go to a planet a 100 years light years from us, spend 24 hours looking around and grab something to eat and then jump on the light beam and be back on earth only 24 hours older whereas you are dead and long gone when I arrive back on earth....

My atomic clock will show 24 hours have passed, during my tour and look around but your clock will show far far far more times has passed.

If you travel at the speed of light it will take you 100 years to reach a planet 100 light years away. That's how long it takes a photon from that star to reach us

 

[Frothingslosh]

If a force causes us to de accelerate does time speed up for us and does our mass reduce. What happened to the Apollo astronauts when Stage 3 shot down at about 26,500 mph and they "slowed" to about 3000 mph when they were about 30,000 mile from the moon.

A second variation on the question. When stage 3 shut down they were in free fall. Let's say instead of just stage 3 just shutting down there were retro rockets fired that reduced their velocity from 26,000 mph to 0. Would time speed up for them and would their mass be reduced.

The point you're missing is that there is no such thing as de-acceleration. Period. Doesn't exist. Ever. Faulty mental construct. Not a real thing.