DARTH said..

sasquash said..

Adriano said...
Absolutely. It's a footnote for GR. My point was that a fundamental understanding of gravity would be incredible for humanity.

In the meantime, the LIGO will provide plenty of research hours and theorising. It's is but one small step on the long path to understanding how gravity works through space-time.

Carantoc misunderstood what I was saying and instead went on the usual HW style ad hominen diatribe when he's actually talking about a different thing altogether.

quickly...tell yourself your smart....

notmillsey?

More likely notsane.

actiomax said..
Jupiter
I could be wrong but i think its because time is relative to the observer .
Eg you have reached the event horizon and you look at your watch it seems to be ticking like normal but to a person outside of that looking at you time has stretched
when you observe time tick one second the observer see the same one second takes a minute hence time is stretched.
Hope that helps .

actionmax
Thank you for the answer. So there will be an "actual time" and an "apparent time"?

The "actual time" or "absolute time" is the mechanical clock that is ticking away regardless of where you are. Lets say I have 2 clocks. One is sent flying off towards a black-hole, and one stays with me. The 2 clocks will tick in sync regardless of where they are. By the way, I believe Joe Hockey knew where all the black-holes are.

The "apparent time" or "relative time" is the time observed by the second party. Lets say I was sent flying off towards the centre of a black-hole. While I was at it, I was eating a bowl of Weet-bix. The time it takes to shovel a spoon of the stuff into my mouth is 1 second. So within a time span of 10 seconds, I shoveled 10 spoons. Would an observer sitting on earth see 10 spoons in the 10 seconds,, or he only sees 5 ? If he only sees 5, where would the other 5 go? Would he have another 5 extra seconds to see me shoveling the next 5 spoons? In other words, he sees my spooning action banked up due to "time stretch". If so, does it mean there will be a delayed replay for everything, when observed from earth ?

Adriano said..
Clocks and people can be made to run more slowly.

can run faster too ?

Adriano said..
Not sure about that. That would violate the known laws of the universe wouldn't it? I mean gravity slows time by distorting the space-time continuum which exists in perpetuity, so it's not theoretically possible for gravity to accelerate time methinks. The space-time continuum is DISTORTED - not violated

Perhaps there is another way?

Macroscien said..

Adriano said..
Clocks and people can be made to run more slowly.

can run faster too ?

Relatively on earth, time can run faster.

A climber's time is passing slightly faster at the top of a mountain compared to people at sea level.


Easy to see why Einstein was Time's Person of the 20th Century.

I read all the posts here, and I am still confused than ever about (1). Time gets stretched due to gravitational flow, and (2). What time really is.

Someone put up an argument that an atomic clock becomes slightly slower on higher altitude such as in orbit. Could it because the lower gravitation force acting on the atoms play a part? For example, water boils because of the degree of agitation of molecules within it. Lower pressure at a higher altitude caused water to boil at a lower temperature. Could a weaker gravitational force have affected the molecular behaviours of the Caesium atoms?

What is TIME? In the good old days, time is measured by all manners of criteria. How long does it take to walk to the next village? Two full days. It could have been 1 day and 20 hours, or it could have been 2 days and 2 hours. But it was 2 days as we didn't have clocks. Then we have the egg-timers, or water clock, or solar clock. They were rough as guts until the pendulum clock was invented. Even that was nearly rough as guts as the pendulum can be affected air resistance.

Regardless of what kinda of time measuring device, or how they operate, they are based on our earth time, ie 24 hours/day, 365.25 days per year. So 1 tick is 1 second. 3600 ticks in an hour.

I believe TIME is only an arbitrary measure of duration. It came, and it went. If you begin taking notice of the time you went to bed, and you know how many hours you slept when you got up. However, it you didn't care, time and the duration of your sleep have no meaning whatsoever.

Take another example. A drummer hits his drum at a steady rhythm at 1 beat per second. If you are to transport him to a far away planet, would his drum beat still be 1 beat/second? I would say it will be. Now can you argue that looking from earth, he is now hitting his drum at a slower rate? That may be because of the distance of transmission between earth and the distant planet.

I do find the idea of Time Warp due to gravity a bit far fetched because, time is, in essence, an arbitrary measure defined by us.

Jupiter said..
(2). What time really is.

It is arbitrary as far as the units go. Although it helps if you have a unit that can be divided into smaller units accurately.
H:mm:ss is great for working our where you are in the Earth day but not really relevant when measuring anything else outside of earth (other than to give a comparison to Earth)
Decimal time is way easier for computers to work with. (Check how MS Excel actually stores date time values)

The units have to be able to be synced though. Systems that rely on clocks ie GPS would not work at all without clocks being in sync.

Being able to measure, and account for, relativity means the difference in clocks between Earth & Space is better corrected therefore more accurate GPS readings can be made.

^^

I didn't bother replying to Adraino at the time as he seemed a bit wound up about the whole thing.

But yes, what he wrote seems to be nonsense.

If you are in a box suspended above earth, but stationary (say hanging from a crane) then your feet feel a reaction to the floor of the box equal to your mass x 9.81m/s/s due to the effects of gravity (or about 9.81m/s/s depending exactly where you are).

If you are in the same box in the middle of space and the box is accelerated at 9.81m/s/s the sensation you feel is exactly the same, your feet reacting against the box at your mass x 9.81m/s/s.

And for every other part of your body the sensation in both case is exactly the same as well. Your muscles do not have a different sensation from your bones in one and not the other. I have no idea how you can contort that statement into "no you misunderstood because you are a fool, what I clearly meant was ...".

The formula defining what is happening it is exactly the same (perhaps that what he meant when he said F=ma (I assumed he was jabbering on about FEMA again, probably made a typo with the E to an =, perhaps he was saying FEMA conspired the whole gravity thing or something, who knows what it meant ?). But yes, you would have no knowledge whether you are accelerating through space or stationary next to an object influenced by its gravity.






So in answer to your observation (assuming there is no window you can look through and the question is answered in a more philosophical way) first I came up with this idea :

To tell which it is you have to wait. Yep, just wait and do nothing.

Because, I thought, gravity would remain constant forever but you can't accelerate forever. Eventually you reach the speed of light or you get to the edge of the universe.

But then I realised you still wouldn't be able to tell because I think in both situations you would then simply gain mass instead of gaining speed. So the effect you felt would be the same. You still wouldn't be able to tell if you were gaining mass or gaining speed. So you could still be subject to the force that was causing acceleration (or the force from gravity) and you still couldn't tell.



So, I am sure there is some sort of answer (a philosophical answer that is). Might have to ask a six year old though. Their logic is often better in these situations.


Maybe the colour of the box matters and it involves a melting snowman in some way as these things so often seem to ??!!

Adriano said...
Not sure about that. That would violate the known laws of the universe wouldn't it? I mean gravity slows time by distorting the space-time continuum which exists in perpetuity, so it's not theoretically possible for gravity to accelerate time methinks. The space-time continuum is DISTORTED - not violated

Perhaps there is another way?

Travel fast.

For an electron, traveling at the speed of light, the universe begins and end in no time at all. And it's shape is flat in all directions.

Although this one I don't understand and I'm just repeating what I've read. Isn't speed relative? Who's moving?

Carantoc said..
^^

I didn't bother replying to Adraino at the time as he seemed a bit wound up about the whole thing.

But yes, what he wrote seems to be nonsense.

If you are in a box suspended above earth, but stationary (say hanging from a crane) then your feet feel a reaction to the floor of the box equal to your mass x 9.81m/s/s due to the effects of gravity (or about 9.81m/s/s depending exactly where you are).

If you are in the same box in the middle of space and the box is accelerated at 9.81m/s/s the sensation you feel is exactly the same, your feet reacting against the box at your mass x 9.81m/s/s.

And for every other part of your body the sensation in both case is exactly the same as well. Your muscles do not have a different sensation from your bones in one and not the other. I have no idea how you can contort that statement into "no you misunderstood because you are a fool, what I clearly meant was ...".

The formula defining what is happening it is exactly the same (perhaps that what he meant when he said F=ma (I assumed he was jabbering on about FEMA again, probably made a typo with the E to an =, perhaps he was saying FEMA conspired the whole gravity thing or something, who knows what it meant ?). But yes, you would have no knowledge whether you are accelerating through space or stationary next to an object influenced by its gravity.
.......

Completely fundamentally wrong. Gravity works on every atom/subatomic particle with mass of your body. An externally applied force such as a rocket engine firing reacts with one surface of your body.

Totally different sensation.

Ian K said...

Adriano said..



Completely fundamentally wrong. Gravity works on every atom/subatomic particle with mass of your body. An externally applied force such as a rocket engine firing reacts with one surface of your body.

Totally different sensation.

Totally the same sensation. And reversible! Accelerate in the same direction as gravity to cancel it out. Indistinguishable from deep space.

Not the same. The plane is in a steep dive and those people, who appear to be floating gently are falling, due to gravity, as if skydiving but are protected from wind resistance.
When the plane levels out, gravity pulls them against the floor.
Gravity is not cancelled out.

Adriano said..
......................................The clock in the satellite still ticks, but slower.

It actually ticks quicker when taking into account the aggregate of both General and Special Relativity. If not adjusted then positioning data ends up out by 11km /day.
Skip the first 30seconds - it's relatively a waste of time In fact just go to around the 2 minute mark.

sls said..

Ian K said...

Adriano said..



Completely fundamentally wrong. Gravity works on every atom/subatomic particle with mass of your body. An externally applied force such as a rocket engine firing reacts with one surface of your body.

Totally different sensation.

Totally the same sensation. And reversible! Accelerate in the same direction as gravity to cancel it out. Indistinguishable from deep space.

//

Not the same. The plane is in a steep dive and those people, who appear to be floating gently are falling, due to gravity, as if skydiving but are protected from wind resistance.
When the plane levels out, gravity pulls them against the floor.
Gravity is not cancelled out.

It is the same. Resisting gravity is the same as feeling a 1g acceleration. In free fall you don't feel the acceleration until it is resisted.

Adriano said..

evlPanda said..
What's always tripped me out is that you can't tell gravity from acceleration.

Put me in a box and I might be near a large body, or I might be accelerating. I can't tell. Either way I'm at 1g.

Interesting. There is a difference though. If you mean accelerating like an external constant force is pushing the box then you will feel it through the box on one side of your body as acceleration and pressure on tissues.

Gravity acts on every bit of matter in your body and that's why it is different - pulling at various amounts depending on density. Muscles more than bones for instance.

F = ma

Wonderful stuff.

Just to remind us of what we're talking about. Gravity and acceleration - not always the same sensation.

Adriano said..

Ian K said..

Adriano said..



Completely fundamentally wrong. Gravity works on every atom/subatomic particle with mass of your body. An externally applied force such as a rocket engine firing reacts with one surface of your body.

Totally different sensation.

Totally the same sensation. And reversible! Accelerate in the same direction as gravity to cancel it out. Indistinguishable from deep space.

No look - we're talking about the "sensation" of gravity compared to any type of acceleration equivalent. One acts on one side of your body and the other every atom. The net vector displacement may be the same but the sensation is totally different. Try the difference between whiplash and 5g applied as gravity. Totally different feeling as a human. That's what we're talking about - not the net resultant vector or displacement.

Try looking at it from the perspective of inertia. Gravity acts on every atom. Every atom has inertia. The force felt through your feet must be transmitted/distributed through your body in exactly the same way. Exactly the same sensation in both cases.

A quote from the man himself

" we [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.
<div class="templatequotecite">— Einstein, 1907 "

en.wikipedia.org/wiki/Equivalence_principle

Ignoring the patronising tone from Carantoc and moving on, I'm not disputing the Einstein Equivalence Principal, that is not in debate - it's fundamental. We're talking about "how it feels" in a real experiment.

The principal deals with the effect on all "bodies". We have a brain and can feel the forces as well as measure the resultant vectors. The assumption by Ian is that inertia and gravity feel exactly the same to a human. I'd like to see his experiment on that.


"The Einstein equivalence principle has been criticised as imprecise, because there is no universally accepted way to distinguish gravitational from non-gravitational experiments (see for instance Hadley[35] and Durand[36])."

So to prove what you're saying is correct, you first need to do a verifiable universally accepted experiment and so far - that's not possible.

Also Carantoc, don't forget Ian thinks steel skyscrapers are built with cold formed light steel. We all make fundamental mistakes but ever hold hope that minds can remain open.