What does moving through Space and Time mean?

in #steemstem5 years ago

It is very easy for satellites to get an accurate position of a body on earth to a range of few centimeters. Everybody, whether travelling on land, air, or sea can easily get a “fix” of their locations by merely pressing a knob on a small receiver. So, to obtain such a pinpoint ground position, the receiver requires to communicate with close to four satellites. Three of the satellites are required to get the position “fix” while the fourth checks on the first three for accuracy.

Locating where precisely you are on Earth is a factor of the combination of astronomy and clocks. The time gaps between the signals from the positioning satellites have to be calculated to a very high degree of accuracy. For instance, a hand-held receiver can show when you move a few steps, by measuring the time that radio waves take to move that extra distance. The first significant initiative in making accurate clocks to help in navigation was made by the watchmaker, John Harrison in the 18th century. He was later awarded a prize by the British Government for making a clock that was accurate enough to help a navigator work out his position from astronomical observations to a precision of less than 2 km.

hourglass-1875812_1280.jpg

Source: pixabay, FunkyFocus, CC0

The positions in space of the 24 satellites of the Global Positioning System (GPS) need to be accurately known, so they are constantly monitored from fixed ground stations. The satellites release positioning signals through the use of ultra high-frequency radio waves. From the time delay at each ground station the precise position of each satellite is calculated. The position monitoring has to be continuous. Ionized layers that arise and disappear in the atmosphere slightly alter the radio wave speed thereby causing the satellites to also vary slightly in position with time.

It is now very common to see GPS receivers in cars. The data collected enables the car’s position to be calculated to a distance which is close to 2 metres. This position is linked to a map stored in the receiver memory which is displayed and the receiver gives visual and spoken directions to a destination input by the driver. Several correction factors are used to manage such things as signal delays, unwanted reflections or absorption of the signal. The key item that allows this is a highly accurate measurement of time: each satellite contains the most accurate clock of all, which is an atomic clock. Generally, clocks measure the passage of time using a regular repeated change of some kind, such as a pendulum or a vibrating quartz crystal but an atomic clock makes use of the constant frequency of the radiation emitted by a particular isotope of caesium.

drive-863123_1280.jpg

A GPS device giving directions
Source: pixabay, Foundry

THE IDEA BEHIND MOVING THROUGH SPACE AND TIME?

Movement, or better still, motion is one of the most important topics in the study of physics, with its relevance beneficial to our daily lives. For example, in conveyance, pilots and drivers need to know how fast trains, aircraft and cars are moving, so that they can be able to control and guide them. It’s important also for the planners to know this so that they can plan their timetables ahead. At an atomic level, knowing about the movement of particles has led to explanations of the behaviour of solids, liquids and gases. But motion is somehow cumbersome. On a normal journey the driver may make up to thousands of changes in speed and direction. Similarly, particles of gas are invisible, so how can we even think of monitoring their movements?

In the past, the true study of motion began with trying to forecast the movements of the Sun, the Moon, the planets and the stars. At the time, people believed that the Earth was at the centre of the Universe and everything else moved round the Earth in some way. People also believed that the stars and the planets had an effect on their lives and behaviour, and so needed accurate data to help them make astrological predictions. For almost 2000 years the important ideas about motion were due to the Greek scientist and philosopher Aristotle (c.348-322 BC). He didn't see the need to explain why things moved like why the smoke rose and the apples fell from trees because he felt it was just natural for them to do so. This led him to make some mistakes about falling objects and the motion of an arrow. Also, speed was not the important feature of everyday life that it is today. People moved slowly - on foot, on horseback or on sailing ships. Clocks were rare, and measured time no more accurately than to the nearest minute.

FOCS-1.jpg

Atomic Clock FOCS-1 (Switzerland). The primary frequency standard device, FOCS-1, one of the most accurate devices for measuring time in the world. It stands in a laboratory of the Swiss Federal Office of Metrology METAS in Bern.
Source: Wikimedia, METAS; public domain

In the seventeenth century, many of these aspects of life began to change. First there was a great increase in trade worldwide. As a result, there was a need to improve the skills of navigation. It was far more difficult to navigate a ship across an ocean than it had been simply to sail along the coast. The positions and movement of the Sun, the planets and the stars now needed to play a far more important role - as an aid to navigation, rather than for fortune-telling. At the same time, the use of gunpowder was making the technology of war more sophisticated, with the development of cannons. The Italian physicist Galileo Galilei (1564-1642) studied the behavior of moving objects and so helped to explain the movement of cannon balls. This further explained how cannons could be fired more accurately.

The results of these studies of motion in the 17th century was that scientists had vey dear ideas of how to measure the quantities involved in motion which are the distance, time, velocity, speed, and acceleration. The study of motion on its own is called Kinematics. When forces are taken into consideration, the study becomes known as Dynamics. Some of the world's most well-known physicists such as Galileo, Newton, and Einstein in particular did their greatest work on the motion of objects.

The study of motion led to the development of accurate measuring instruments such as telescopes, chronometers, atomic clocks and satellites for ocean navigation, radar, and lasers for surveying. Studying motion has also made physicists think deeply about the nature of space and time, and has led to theories about gravity, special and general relativity, and the origin and expansion of the Universe. Some of these more advanced ideas will be written on in some of my subsequent posts.

Coming back to the matter at hand, before we look closely at the movement of objects, we first need to see how the necessary measurements are made, and how the units of measurement have been established. In particular we shall review the use of light as the basis of many measuring techniques today, and measurements of distances ranging from the small scale to the scale of the Universe.

THE “TIME” USED TO MEASURE DISTANCE


In moving, an object changes its position in space, so we need to be able to measure distance. Moving takes time, so time also has to be measured. In practice, we are often more concerned with time than distance, as these common statements show:
Car for sale. Ten minutes from the car park.
Lagos is just two hours from Ibadan, travelling by bus.

The signposts of footpaths occasionally tell you the time it will take you to walk somewhere, rather than the distance. An assumption is being made about the speed of travel.

Measuring distances with electromagnetic waves, but still using time.


Using time units to measure distance may seem strange, even 'unscientific'. Yet time is in fact the basis of most modern ways of measuring distance. Air traffic controllers use the time it takes radar pulses to travel to and from an aircraft to chart its position in a crowded flight pattern. Surveyors use the time-of-flight of a pulse of laser light to measure distances accurately. Cartographers making accurate maps now use radar or laser beams. On the scale of distances in the Universe, astronomers also use radar to establish the precise positions of planets. As in the table below, they measure far vaster distances in the time units based on the speed of light, light seconds and light years.

pocket-watch-3156771_1280.jpg

Source: pixabay, annca; CC0

Some distances in units of length and in time units

ObjectAverage distance from earth in metresTime units
Geostationary satellite4.2×1070.141 s
Moon3.844×1081.282 s
Sun1.496×1011499.0 s
Sirius8.2×10168.7 year
Andromeda galaxy2.1×10222.2×106 year
First galaxy2.0×10262.2×1010 year

Time unit (in seconds) = distance of an object (in metres) divided by the speed of light (in metres per second).

All these techniques depend on the measuring signal, light or a radio wave, having a constant speed. Many of the applications rely on the fact that electromagnetic waves are easily reflected, especially by metals. Both radio waves and light waves are electromagnetic waves of constant speed (when travelling in a vacuum). Light is now recognised as such a fundamental and useful measuring tool that the SI unit of distance, the metre, is defined in terms of the speed of light. Thus, a metre is the distance travelled by light in a vacuum in the fraction 1/299 792 458 of a second.

Where does the number 299 792 458 come from? To understand this, we need to be aware that the metre, is one of the seven fundamental units that have been agreed on by scientists internationally, while other units are defined in terms of these seven. Just to refreshes our memory, the seven basic fundamental units still remain the kilogram, metre, second, Kelvin, mole, and candela. And another basic unit relevant here is the second, defined in terms of the vibrations of a caesium-133 atom.)

In 1983, it was decided that the distance light travels in a vacuum in this very tiny fraction of a second would be the new definition of a metre. This means that light is defined as travelling at a speed of 299 792 458 metres per second, which is also the speed of all electromagnetic waves in a vacuum. The speed is given the symbol c, and we can say that:

distance (m) = c (ms-1) × time of light flight (s)

This is a use of the familiar formula:

distance = speed × time

x=v × t

An air traffic controller plotting the movement of an aircraft several tens of kilometres away is making more direct use of the light-distance relationship. This is because the distance of the aircraft is measured by radar waves with a 'time of flight' to the aircraft and back that is accurately measured using a quartz clock.

A sample problem on distance and time in a real life situation.


Let’s assume an air traffic controller uses a radar rangefinder and measures a time of 0.50 milliseconds for a radar pulse to go to and return from an aeroplane. How far away is the aeroplane in metres?

To solve this problem, we need to assume that the radar pulse takes the same time to go out as to come back, then the aeroplane must be at a distance of 0.25 light milliseconds.

Distance in metres = c × time of light-flight
= 2.997 924 58 × 108 × 0.25 × 10-3
=7.2 × 104 m

Note that the limit on the accuracy of this measurement allows us to give the final answer to only two significant figures. In practice, radar range finders can do a lot better than that. But in most cases, the value of c is taken to be approximately 3.00 x 108 ms-1

MAPPING WITH LIGHT

Making modern maps of places on Earth involves the surveying technique called Triangulation. This is carried out either on the ground or by using survey satellites. The technique relies on two of the properties of light i. e Light beams travel in straight lines and at a known speed

Triangulation is a technique that was used, and probably invented, by the Ancient Egyptians. Simple triangulation needs a base line of carefully measured length, let’s say AB. Two distant objects (X and Y) are chosen. The angle each object makes with the base line is measured from each end of base line. Then the distances to the objects are found using simple trigonometry. Nowadays a laser surveying instrument measures a distance in light seconds and converts this measurement into metres.

Triangulation-boat.png

Triangulation
Source: wikimedia, Svjo Own work; CC BY-SA 4.0

The accuracy of maps made using triangulation depends on very reliable clocks. Angles are also measured with great accuracy, but cannot be measured as exactly as light-times. However, a long base line increases accuracy, and accurate maps are based on lines many kilometres long.

How far away are the stars?

Stars are too far away for their distances to be measured using a base line drawn on Earth. But astronomers noticed that some stars appeared to move relative to other stars as the Earth moved round the Sun. They concluded that this effect was the same as you see when you move in front of a window: a point on the window frame appears to move against the background of more distant objects. This effect is called parallax, and for stars it is called stellar parallax.

During the nineteenth century, the parallaxes of thousands of stars were measured, and hence their distances from Earth were calculated. But many stars showed no detectable parallax. They were too far away for the annual motion of the Earth across a distance of 3 ×1011 metres to make any measurable difference to their apparent position. In particular there was a class of bright cloudy objects that showed no parallax, and astronomers concluded that these objects (called nebulae, the Latin for ‘clouds’) must be on the fringes of the Universe.

FRAMES OF REFERENCE

How fast are you travelling at the moment?

The answer may seem to depend on whether you are reading this post on a train that is travelling at 120 km h-1, a plane travelling at 1000 km h-1 or just sitting at your desk. But in fact, as the question stands, it is meaningless. Even if you are at your desk, both you and the desk are spinning with the Earth at a speed of just over 1000 km-1 (if you are at the latitude of London). The Earth itself is moving in an orbit round the Sun at a speed of 107 000 km-1. The Sun, and its Solar System, are orbiting round the centre of the Galaxy at a speed of almost 1 000 000 km-1. You are not, of course aware of any of these movements. The coffee in your cup is unshaken by these astronomical speeds. The question at the start of this section makes sense only when you add words such as ‘relative to the room' or relative to the Earth or ‘relative to the Galactic centre’.

Wikipage_pic.PNG

Reference frame
Author: TheGreenOne

This is the simple principle of relativity first stated by Galileo in the 17th century. His ideas of relativity were developed much further in the early 20th century by Albert Einstein. Much of the time we take our measurements relative to the Earth, which we assume to be still and our normal frame of reference. This phrase simply means that the measurement we make are with reference to our static selves and the fixed objects that surround us. So, when we measure in an experiment that a dynamics trolley is moving at 0.55 ms-1, we take it for granted that this motion is relative to the walls, floor and laboratory bench. We don't keep asking ourselves, relative to what?" But we have some interesting problems to solve when our personal reference frame is moving relative to the Earth, as when it is a ship at sea, an aircraft in flight or a canoe on, say, a tidal river.

MOVING FRAMES OF REFERENCE

The equations of motion apply just as well inside an aircraft moving at speed relative to the Earth as they do for an object on the fixed Earth itself. If you drop a pen to the floor of an aircraft, it will seem to you to move in exactly the same way as it does in your classroom on Earth. You don't need to take into account the fact that in the three-tenths of a second it takes to fall, the pen also moves forward a distance of a hundred metres or so. You too are moving forward at the same speed, so relative to you the pen falls straight downwards. You and the pen share the same reference frame which is the aircraft. For both you and the pen, you could use the equation

v = at
to calculate the speed of the pen when it hits the floor.

Reference_frame_and_observer.svg.png

Reference frame and observer
Source: Wikimedia, Maschen; CC0

Galileo, who used a sailing ship as his example of a moving frame, was aware of relative motion. He needed this idea to explain why the Earth could move without our noticing its movement. Galileo's time to understand that the Earth could possibly move without leaving behind everything on it i.e the sea, ships, the air and flying birds as it is for people today to grasp Einstein's theories of relativity.

Real life situation on how to calculate time at different frame of reference.


Assume a canoe club plans a return trip on a river that flows at an average speed of 2.5km/hr. The canoeists will first paddle their canoes upstream for 5km, then return. The leader estimates that the group can paddle at an average speed of 3.5km/hr on still water.
(a) How long should the leader expect the trip to last, ignoring any stops for rest or refreshments?
(b) What is the group’s expected average speed for the journey?

To know how long the leader should expect the trip to last, he needs to understand that the frame of reference is provided by the fixed Earth, with a map distance of 5km each way for the trip.

So, going upstream, the canoe speed relative to the water is 3.5km/hr, but relative to the river bank it is only 1km/hr i.e

(3.5 - 1.5). t = x/v = 5/2 = 2.5 hours.


So the group will take 2 hours of paddling time to reach their up-river destination.

Returning downstream: The distance is still 5 km, but now the speed relative to the bank is 5 km/hr i.e

(3.5 + 1.5). t = x/v = 5/5 = 1 hour.

The group should cover the distance in just an hour.

To get the group’s expected average speed for the journey, one needs to consider the time for the total journey which is 3.5 hours i.e (2.5 + 1) and the canoeists travel 10 km at an average speed of (relative to the solid Earth) of 2.85 km/hr.

Till next time, I remain my humble self, @emperorhassy

Thanks for reading.

REFERENCES


1. What is the difference between moving through space and moving?
2. What Does Moving Through Space-time Mean?
3. Relativity abyss.uoregon.edu › lectures › lec06
4. Einstein's Theory of General Relativity: A Simplified Explanation | Space
https://www.space.com › 17661-...

5. Theoretical physics: The origins of space and time : Nature News & Comment
https://www.nature.com › news › theoreti...

6. Time in physics - Wikipedia
https://en.m.wikipedia.org › wiki › Time...

7. Web results
Spacetime - Wikipedia
https://en.m.wikipedia.org › wiki › Space...

8. Space-Time - Special and General Relativity - The Physics of the Universe
https://www.physicsoftheuniverse.com › t...

9. Web results
Space-Time – The Physics Hypertextbook
https://physics.info › space-time

10. Time dilation - Wikipedia
https://en.m.wikipedia.org › wiki › Time...

11. How fast are we moving through space? – Starts With A Bang! – Medium
https://medium.com › starts-with-a-bang

12. Time Travel: Theories, Paradoxes & Possibilities | Space
https://www.space.com › 21675-...

13. Triangulation
14. Collins Advanced Physics by Ken Dobson, David Grace and David Lovett Chapt. 1; pg 1

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I'm always fascinated by the subject of the GPS. We often take it for granted inputting location names on our smartphone and out comes the location precise to the dot. I wonder if the world would ever function as we know it if we are to go back to the Pre-GPS era when all we had was some old dusty map to navigate our ways to various locations.

You are always on point with your comments. I really commend the time and effort you put in reconnoitering posts, reading and commenting on them. I really wish to emulate you.

Big thanks for coming by, @greenrun.

An interesting piece on moving through space and time. More interesting is the fact that everything seems to have been captured by Einstein theory of relativity. Better still, this your write up reminds me of Heisenberg uncertainty principle but while that primarily applies to particles at the atomic level, I am just here wondering if it is relevant to what you just discussed.

Physics is a very broad knowledge and all those principles are interrelated.

Thanks for coming by @gentleshaid.

Very complete and educational article! I wonder, what is your opinion on the possibility of time travel, knowing that in truth, one would have to travel not only through time, but through space as well?

It amuses me to imagine the existance of a machine that allowed travel through time, that could take one to, say, 1986, but that would also leave one at the very same place in space from whence one came from. Probably floating in space.

Posted using Partiko Android

Hello @mike961!
Thanks for coming by.

Here's a [link](http://www.physics.org/article-questions.asp?id=131) to share my view and to explain further on time travel.

Thanks! Checking it out right now

Hello, @mike961. To further answer your question, I've already started writing some series of posts on physics of space and time encompassing Einstein's theories, time dilation, length contraction and some part of general relativity. Whether even the general theory works.

So, watch out for those posts and I'd really appreciate your comments on them.

Got it, already followed you, I'll be on the lookout for more posts like this one ;)

Posted using Partiko Android




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The thought occurred to me now that names like 'the theory of relativity' bolster the impression, among some people, that everything is subjective. (Even though there's no relation between Einstein's physics and, for instance, morality, still the name itself can act as a psychological booster to the idea that all impressions are subjective.) But actually, it could equally well have been dubbed 'the theory of objective relations', because once you decide on a frame of reference, the relation is objective.

You are absolutely correct, Alex. Even anybody who's clever enough can come up with ingenious theories about the universe, relativity and what have you. But it's just that the success of a theory lies in its explanatory power and its predictive ability. Part of what Einstein came to do was to explain a fact that Newton's laws couldn't.

Thanks for coming by, @alexander.alexis

I was thinking in a similar way @gentleshaid commented. So I apologize not referring directly to your topic but indirectly.

If the world could be explained absolutely physically, we could predict the weather exactly. However, we cannot do this in this absoluteness, since we do not know the exact starting point or state of the factors influencing the weather. This weakens predictability.

Quantum physics gives us answers that raise new questions and as far as I have read, those who deal with quantum mechanics say that there is no possibility of measurement because the measurement itself affects quantum motion and therefore makes it unpredictable and can only rely on probabilities.

Newton's view of the world has left us with a way of looking at things that sees everything as matter and thus all entities as material, i.e. physical. Some say that there is nothing but matter, therefore any explanatory model that refers to immaterial processes must either be irrelevant or wrong. Since there can be no such thing as immateriality.

If one understands the universe as a space where all processes are based on the physical laws known to us, then one inevitably has to assume a determinism that needs a starting point, like the Big Bang that set all things in motion. There is no intelligence or beauty integrated in this game of movement, everything is an unbroken chain of causal connections. The universe is perceived as inanimate, mechanical, not organic.

If one compares the quanta with humans in the universe, these quanta would probably also "say" that the surrounding universe follows its determination without knowing, for example, that a human organism encompasses them. This organism does not seem to behave intelligently, nor does it behave intelligently in relation to its quanta, but when viewed from the outside and as a whole, it does behave intelligently.

Now there are people who do not like the totality of physical events as "laws" and ask whether the laws could not also be "habits", which appear to us to be legitimate. In fact, the time scales we can capture from a human perspective are so great that we cannot really know if a law is not a universal habit. Which can also change. For example, a system of bodies moving in space could create a new habit through chaotic events that represent a radical novelty.

"Law" is a linguistic, i.e. human concept and means that something has always been the way we can measure and calculate it at present. But since we can't really really define the term "always" and "everywhere" with certainty, it seems interesting to also approach the concept of "habit" and see how this aspect could change the view of the universe and what we call "living".

So, how would you call the universe? Would you say "it lives"?

I am not so much interested in proof as in a changed view of the living. It is more sympathetic to me not to regard our universe as a mechanism that once set in motion, stubbornly follows the determined pathways. I flirt with the idea that there are influences that could exceed our understanding, measurement and calculation framework.

Why do I do this? Because I believe that this influences the human psyche and Newton's view led us to a more presumptuous attitude of controlling and predicting everything. However, a physically objective world has an influence on the subjective perception of us humans. My guess is that if we include less determinism and more unpredictability in our considerations, we will have more respect for the unresolved questions.

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