# The Naked Scientists Forum

### Author Topic: What is distance?  (Read 3725 times)

#### thebrain13

• Sr. Member
• Posts: 442
##### What is distance?
« on: 15/06/2006 20:46:25 »
modern physics states that the strength of gravity and electrical charge becomes weaker the farther away an object is from it, expressed by the inverse square law c=1/d^2. Since absolute distance has been abolished by relativity. I was wondering, what exactly distance is. Einstein states that gravity warps distance, how can you warp distance if it doesn't exist?
« Last Edit: 09/07/2006 22:53:20 by thebrain13 »

#### another_someone

• Guest
##### Re: What is distance?
« Reply #1 on: 16/06/2006 00:33:03 »
Distance (or length, which is the same thing) has always been relative in some way.

Between 1895 and 1960, it was relative to a bar of platinum/iridium measured at the melting point of ice.

From 1960, is is the distance covered by light emitted by krypton-86 in a vacuum in a given unit of time.  Ofcourse, that requires a measure of time, which itself is relative to the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

The issues of the impact of relativity are significant, and this is how Einstein explained a magnetic field as a relativistic manifestation of an electric field.

http://en.wikipedia.org/wiki/Magnetic_field
quote:

n physics, a magnetic field is the relativistic part of an electric field, as Einstein explained in 1905. When an electric charge is moving from the perspective of an observer, the electric field of this charge due to space contraction is no longer seen by the observer as spherically symmetric due to non-radial time dilation, and it must be computed using the Lorentz transformations. One of the products of these transformations is the part of the electric field which only acts on moving charges - and we call it the "magnetic field".

George

#### thebrain13

• Sr. Member
• Posts: 442
##### Re: What is distance?
« Reply #2 on: 16/06/2006 02:38:02 »
yes you can say that distance is relative to how far(notice far is another term for distance)light from krypton-86 in vacuo travels given a specific duration of time. however lets say that light from krypton-86 takes eight minutes to reach the sun. There are no platinum bars in empty space to set the speed of krypton relative to, so why does it take that specific length of time to complete the trip. The answer is there are eight light minutes of space between the sun and the earth. you must traverse a billion light years to reach a distant galaxy, you must traverse eight light minutes to reach the sun. but what exactly is it that is so different about the sun and the distant galaxy, that makes light take more time?

#### another_someone

• Guest
##### Re: What is distance?
« Reply #3 on: 17/06/2006 01:23:47 »
quote:
Originally posted by thebrain13
yes you can say that distance is relative to how far(notice far is another term for distance)light from krypton-86 in vacuo travels given a specific duration of time. however lets say that light from krypton-86 takes eight minutes to reach the sun. There are no platinum bars in empty space to set the speed of krypton relative to, so why does it take that specific length of time to complete the trip. The answer is there are eight light minutes of space between the sun and the earth. you must traverse a billion light years to reach a distant galaxy, you must traverse eight light minutes to reach the sun. but what exactly is it that is so different about the sun and the distant galaxy, that makes light take more time?

It is the kind of question that can be taken at a great many levels.

At its simplest level, since distance is defined in terms of time and the speed of light, so that is all there is to it.  Something is defined as being twice as far away simply because light (in a vacuum) takes twice as long to get there from here, or here from there.

Ofcourse, we have a lot of everyday prejudices about what distance should mean; but these are everyday ideas of distance rather than a technical definition of distance.

Firstly, distance really only has a common sense meaning within a common inertial reference frame (i.e. if two things are moving relative to each other at speeds close to the speed of light, then a lot of the common prejudices about distance no longer hold true – and the same is true of distance within a gravitational field).  The most extreme consequence of this is distances measured within a black hole.  Since light can never leave a black hole, then simply using the speed of light to measure distance would make the event horizon an infinite distance from the centre of a black hole.  Yet, light can fall into a black hole, and thus the distance from the event horizon to the centre becomes different from the distance from the centre to the event horizon – yet common prejudice dictates that the distance from A to B should be the same as the distance from B to A.  To a very much lesser extent, this is even true of the distance between the Sun and the Earth, since light will travel very slightly faster from the Earth to the Sun than from the Sun to the Earth.

All of the above relates to distance as it is defined by physicists.  In everyday terms, distance is usually regarded more as a matter of how much can you fit between two points.  In the simplest aspect, this goes back to the platinum/iridium standard metre, when you might ask how many standard metres can you fit between two points.  On the other hand, it applies not only to standard metres, but to more everyday objects.  For instance, you might measure a length of road by how many lamp posts separated by a standard distance may fit between two points in the road, or how many houses might you build along a stretch of road.  You might measure a chain by how many links you would fit within the chain.  In each case, the measure of distance is relative, but works by asking mow many of a smaller unit of distance/length you can fit into the larger unit, and then scale that up to how many of the larger units you would fit into yet an even larger unit, and so on and so on.

This does, as with the measure against the speed of light, only really work if the whole system has a common inertial frame (i.e. you cannot say how many links are in a chain if the links keep moving or the chain does not stay a constant length).  In another example (maybe easier to visualise), you could measure the length of a stretch of road by how many motor cars you can fit on the road.  This is simple if the cars are parked, but as the motor cars start to move, then the distance between the cars has to increase, and so the number of cars you can fit on the road reduces.  Even worse, if the road is on a gradient, then the number of cars that you can fit travelling up the road may be different to the number of cars you can fit moving down the road, and so suddenly the distance from A to B is no longer the same (as measured in numbers of cars fitted) as the distance from B to A.

George

#### thebrain13

• Sr. Member
• Posts: 442
##### Re: What is distance?
« Reply #4 on: 17/06/2006 05:11:39 »
great, you gave me the answer I was looking for, lucky im talking to someone who knows what he is talking about. your answer, distance is defined as being twice as far away simply because light(in a vacuum) takes twice as long to get from here to there or from there to here.

so, given this specific definition, even without introducing some liquidy luminiferous aether to set distance relative to. we can now claim that distance itself, or empty space, or aether, or spacetime, or whatever you wish to call it, is now endowed with literal, physical properties. hence it does exist. And it is absolute. general and special relativity both have ways in which distance can be altered, however the distance they are altering is absolute. In otherwords you could say, an object seen moving at 87 percent the speed of light, or under a specific amount of gravitational strength, might be one half its original length, but its original length is at least determined by an absolute frame of reference.

Lastly I believe it is this specific view of distance which allows for the twins to determine who is actually moving relative to the other. Read the post, twin paradox if you wish. and more importantly allows for a consistent definition of what gr and sr are ACTUALLY changing. And what their laws are ACTUALLY based on.

Or maybe thats what einstein was ACTUALLY saying.
Or maybe im ACTUALLY just wrong.[?]

#### Nieuwenhove

• Jr. Member
• Posts: 27
##### Re: What is distance?
« Reply #5 on: 10/07/2006 08:02:01 »
Hi,

The nature of distance is a very fundamental one and has not been satisfactory described in modern physics.
Personally, I believe that at the smallest level, space itself is not continuous but discrete and looks like some complicated net-structure with nodes connected by links. These links have no length themselves but it is the number of links between two separated nodes which can be considered as a length. Compare it for instance with internet connections. When site A is 6 clicks away from site B, the "distance" is 6. Distance defined in this way is a dimensionless number, which is very good. For more details see : http://home.online.no/~avannieu/darkmatter/ [nofollow]

#### another_someone

• Guest
##### Re: What is distance?
« Reply #6 on: 10/07/2006 14:22:03 »
quote:
Originally posted by Nieuwenhove
Personally, I believe that at the smallest level, space itself is not continuous but discrete and looks like some complicated net-structure with nodes connected by links. These links have no length themselves but it is the number of links between two separated nodes which can be considered as a length. Compare it for instance with internet connections. When site A is 6 clicks away from site B, the "distance" is 6. Distance defined in this way is a dimensionless number, which is very good. For more details see : http://home.online.no/~avannieu/darkmatter/

Doe not sound of itself implausible, but the question I have is why should all the intermediate nodes necessarily exist?  Is not distance merely the difference in location between two objects, but without their necessarily needing to exist the intervening locations?

George

#### Nieuwenhove

• Jr. Member
• Posts: 27
##### Re: What is distance?
« Reply #7 on: 10/07/2006 17:59:45 »
Hi,

"Merely the difference in location" is not a good definition as location itself is not defined. Of course, you can define location again with using distance but then one has a circular argument. When the intermediate nodes are there one has no longer a problem. A number is a number, is absolute and defined.

#### another_someone

• Guest
##### Re: What is distance?
« Reply #8 on: 10/07/2006 18:34:35 »
quote:
Originally posted by Nieuwenhove

Hi,

"Merely the difference in location" is not a good definition as location itself is not defined. Of course, you can define location again with using distance but then one has a circular argument. When the intermediate nodes are there one has no longer a problem. A number is a number, is absolute and defined.

Absolute location is more than adequately defined – it is merely an arbitrary tag assigned to the space occupied by something.

I am here – that is good enough.  You are there – that too is good enough.  The problem only occurs when we start to ask where is there relative to here, and it is only then that the question of distance arises.

George

#### heikki

• Full Member
• Posts: 56
##### Re: What is distance?
« Reply #9 on: 13/07/2006 16:50:54 »
quote:
Originally posted by thebrain13

I was wondering, what exactly distance is.

Hi.

Distance is distance.

Si unit m=meter.

When thing A is point 1,
and thing B is point 2,
and these point 1 and 2 is not same point(place),
then between these point can measure distance.

It is not any more complicated and dont need to make it more complicated.

If these point 1 and 2 has distance 1m,
and thing A send something to thing B,
and it take time 1s,
then travell speed of this something to point A(1) to B(2) is 1m/s.

But this dont mean that speed is that 1m/s at all travelling distance,
because that something cannot start to go 1m/s speed and cannot stop 1m/s speed, so  therefore speed is first 0m/s and the travell end also 0m/s.
That mean that some point of this travelling distance that something has maximum speed more than 1m/s.

We can put after 1 many 0 to increacing speed like, 1 000 000 000 000 000, etc. but still this something goes like goes.

Hmm.
Is there any common sence of this writing, but i wrote what i wrote.

Distance is distance between two separate point.

#### The Naked Scientists Forum

##### Re: What is distance?
« Reply #9 on: 13/07/2006 16:50:54 »