The Physics That I Don't Understand, queries seeking replies Options

[visuja]

I rarely stay in a thread where I can't add to the substance.

Thats called 'aa bail mujhe maar' Me ask for thy forgiveness! Me know not what I do or say or ..... O Knowledgeable One ! or probably u dont stay back at a thread where u cant get down to levels of A, B, C ?

Do you really believe that the light 'packets' that are reaching us today from say, Al-Nilam, Al-Nitak (1600 light years away) are the original light-packets? Such tiny things, travelling unimaginable distances over unimaginable time-spans, still exist? Where did they get that much energy?

me can comment on that only once I can distinguish between the two energies associated with the light wave . Mass of particle (photon) that carried this energy can be calculated from einstein's equation ? Now, assuming theres no 'reincarnation' of these photons, what is it that eats up the photon's energy en route to us ?? The invisible 'ether' ?? If so, I'd like to know more, pls :begs: I believe theres no friction on the path between the star and us and so theres very little loss of energy, unless there are gas glouds in between which would reduce the brightness.

Er.. why 87.36% ?? any significance ? and atyantgatimaanata mantra .?? ..is there really something like that ? Or did u just conjure one up ??

[shivani]

my take on a few queries..

Awesome (although I had to draw out a little light cone on my pad to figure that out) ! I finally realize why Einstein chose to call time as an extension of space and merged them together into spacetime. Now, someone just tell me how I can fly at the speed of light ?

We all know that matter and energy are interchangable. Pure energy is electromagnetic radiation—whether light or X-rays or whatever—and electromagnetic radiation travels at a constant speed of roughly 670,000,000 miles per hour.
Also, all of us know the relation between E=mc2 where c is the speed of light/EM radiation.

So for any matter to convert whole of its energy into velocity© or even comparable to it , its mass should be infinitesimally small. And only such matter would be able to travel at the speed of light.
So, Bibhas you would be able to fly at "c" when someone discovers how to break down matter into such small particles and then later reassemble it : ).

If the speed of light is linked to time, then, in the past when the speed of light was definitely more, did time flow faster?

I am slightly confused here. How is time measured?? Is time a constant and the distance a photon travelled the variable?
Or Distance a photon covered is constant and time taken is the variable ?

Why are orbits elliptical and not circular?

Elliptical orbits are a natural result of gravity. Planets do travel at different speeds at different parts of their orbits. A planet moves more quickly when it is closer to the Sun.
The change in speed is due to angular momentum. This is just momentum that is associated with rotation. It is determined by how far the object in question is from the point it is rotating around, and by how quickly it is rotating. Like energy, angular momentum must be conserved. Conservation of angular momentum is why, for example, an ice skater spins more rapidly when she pulls her arms in. As her arms come closer to her body, she must spin more quickly in order to have the same angular momentum. The same is true for planets orbiting around the Sun.
Think of it as a competition. As a planet moves further from the Sun, it slows down in its orbit. Because it is orbiting more slowly, it begins to "fall" towards the Sun, because of the Sun's gravity. As the planet comes closer to the Sun, it speeds up in its orbit, in order to conserve angular momentum. As it speeds up, it can pull away from the Sun. As it moves further away, it begins to slow down, and the process repeats. The result of this constant back-and-forth is an elliptical orbit.

The elliptical orbits of the planets are changing slowly due to the gravitational influences of the other planets. Because these are much weaker than the gravity we feel from the Sun, the changes in planetary orbits are very slow. For example, the basic ellipse of the Earth's orbit is not fixed in space:it gradually rotates or precesses, at a current rate of 0.3 degrees per century due to perturbations by the other planets,most notably Jupiter.
also an interestign reading on this one http://www.grandunification.com/hypertext/Geology.html


and I might be able to attempt no. 3 from Bibhas's list tomorrow .. aaj ke liye dimag ka tubelight off.

Waise that headbang is my fav icon ..like a few who love the wub icon

my fav is Visu.. which represents my state perfectly most of the times.. as lost and clueless as a dodo *grinz*

(Now M enters his photon-powered personal ambulator, and zooms away at 87.36% of the velocity of light (not speed, mind you) - OPPOSITE to the direction of Hits, Bibhas, Shivani and Vivek, hurriedly chanting the atyantgatimaanata mantra)

nigahon se chupkar dikhao to jane.. khayalon main bhi tum na aao to jaane.. aji lakh pardon main chup jayiega .. nazar aayiega nazar aayiyega ..
and opposite jao chahe idhar aao MJ .. all motion is circular afterall

[visuja]

thanks Shivani for that link. Havent visited it yet though . But your explanation does seem to ring a bell about conservation of angular momentum.. some high school basics that I seem to forget

Now that we are reasonably comfortable 'riding' light waves, could we discuss how and why these waves are bent by massive galaxies ??

I presume the basic effect of gravity on light should be the same as that for black holes, exceptt hat for black holes, it is an extreme case. So when light passes near massive objects (stars, galaxies), it get deviated from its path and hence teh massive objects act like a normal lens would do.

How does gravity realy affect light / photons ? By Newton's gravitation law, the photon should have some mass for gravity to act on it. Does E=mc^2 relate the light energy (again which energy!? ) to the mass of photon ? Even if this 'lens' effect is understood in terms of spatial displacement oft he light beam, does it also cause the beam to accelerate / decelerate, much like a sling-shot effect ?? In that case, both space-time characteristics of teh wave would change, and hence the info of the light source that we would infer from this light beam would have to be corrected for both the source's location as well as the 'time' at which the source emitted this light beam.

Am I making any sense ??

I see the Determinism thread is being revived, but Im having ahrd time imagining 3 dimensions! Now to add time to it an then all the other unknown dimensions ! Hence my trepidition to step in there

[kallubhai4u]

well Visu, i got some idea 'bout ur query, but i dint get the whole thing can u xplain a bit, so that it bcomes easier 4 us 2 understand ur probs.

[kallubhai4u]

My understanding of String theory :-

Through the mathematics of quantum mechanics and experimental observation, it was deduced that all known particles fell into one of two classes: Bosons and Fermions  Bosons are particles that transmit forces. Many bosons can occupy the same state at the same time. This is not true for fermions, only one fermion can occupy a given state at a given time, and this is why fermions are the particles that make up matter. This is why solids can't pass through one another, why we can't walk through walls -- because of Pauli repulsion -- the inability of fermions (matter) to share the same space the way bosons (forces) can.

Why string Theory - Particle physics interactions can occur at zero distance -- but Einstein's theory of gravity makes no sense at zero distance.
Relativistic quantum field theory has worked very well to describe the observed behaviors and properties of elementary particles. But the theory itself only works well when gravity is so weak that it can be neglected. Particle theory only works when we pretend gravity doesn't exist. So to speak it is applicable only on very small particles.
General relativity only works when we pretend that the Universe is purely classical and that quantum mechanics is not needed or applicable in our description of Nature. ( eg. stars)

If there were a good quantum theory of gravity, then the particle that would carry the gravitational force would have zero mass and two units of spin. This theorized particle is called the graviton.
Now, a graviton can be added to quantum field theory by hand, but the calculations do not match. This is because particle interactions occur at a single point of spacetime, at zero distance between the interacting particles. For gravitons, the mathematics behaves so badly at zero distance that the answers just don't make sense.
String theory suggested that each particle is actually made of  "strings" : a wiggling tiny thread. Think of a guitar string that has been tuned by stretching the string under tension across the guitar. Depending on how the string is plucked and how much tension is in the string, different musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension.
In string theory, as in guitar playing, the string must be stretched under tension in order to become excited. However, the strings in string theory are floating in spacetime, they aren't tied down to a guitar. Nonetheless, they have tension. The string tension in string theory is denoted by the quantity 1/(2 p a'), where a' is pronounced "alpha prime"and is equal to the square of the string length scale.
If string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. These particles cannot be observed by any experiment.  Then comes the question, if the string can only constitute bosons ( particles that transmit forces) or  fermions, too (particles that make up matter)? Open ended or Closed ended? Both.
Different String theories are classified according to whether or not the strings are closed loops, and whether or not the particle spectrum includes fermions. If fermions are included, there must be a special kind of symmetry called supersymmetry, which means for every boson (particle that transmits a force) there is a corresponding fermion (particle that makes up matter). So supersymmetry relates the particles that transmit forces to the particles that make up matter, and these are called superstrings.
Now how does quantum mechanics apply to strings? For bosonic strings, this question is only answered in the affirmative if the spacetime dimensions number 26. For superstrings it comes down to 10. How we get down to the four spacetime dimensions we observe in our world is another story.
If we ask how to get from ten spacetime dimensions to four spacetime dimensions, then the number of string theories grows, because there are so many possible ways to make six dimensions much much smaller than the other four in string theory. This process of compactification of unwanted spacetime dimensions yields interesting physics on its own.
This period in string history has been given the name the second string revolution.
And now the biggest rush in string research is to collapse the table above into one theory, which some people want to call M theory, for it is the Mother of all theories.

I will try to make another post soon on how the the other 6 dimensions are collapsed into known 4 dimensions. Meanwhile if someone else volunteers for it.. great :-)

itz really gr8 on ur part 2 come up with something like this which is very educative & enthralling. but i would say that these phenomena need a bit more of detailed understanding of Quark ChromoDynamics(QCD). plz put up something on that too. this will make it easier 4 us 2 undersatnd the whole issue.

[visuja]

Ok kallubhai4u-ji,

Let me try and rephrase my query.
A ) Could you tell me how gravity affects light ?? Newton's law says that the two itneracting bodies should have masses to have gravitational effect on each other. Does photon have mass ? If so, is it calculated by Einstein's equation?

B ) Apart from the deflection of light from it original path under the influence of gravity, do photons also get accelerated under the influence of gravity ?? Is it possible to measure what is the spatial deflection and by how much were the photons accelerated ?

I'll try and break down my queries further if you find that I'm asking too many questions at a time.

Thanks,
Vivek

[kallubhai4u]

well i spoke about QCD & i m delivering it....hope u'll like it, plz put ur comments, that way i can correct my mistakes. i got this infi frm:-

http://www.encyclopedia.com/html/q1/quantumch.asp

(QCD), quantum field theory that describes the properties of the strong interactions between quarks and between protons and neutrons in the framework of quantum theory . Quarks possess a distinctive property called color that governs their binding together to form other elementary particles . Analogous to electric charge in charged particles, color is of three varieties, arbitrarily designated as red, blue, and yellow, and—analogous to positive and negative charges—three anticolor varieties. Just as positively and negatively charged particles form electrically neutral atoms, colored quarks form particles with no net color. Quarks interact by emitting and absorbing massless particles called gluons , each of which carries a color-anticolor pair. Eight kinds of gluons are required to transmit the strong force between quarks, e.g., a blue quark might interact with a yellow quark by exchanging a blue-antiyellow gluon. The concept of color was proposed by American physicist Oscar Greenberg and independently by Japanese physicist Yoichiro Nambu in 1964. The theory was confirmed in 1979 when quarks were shown to emit gluons during studies of high-energy particle collisions at the German national laboratory in Hamburg. QCD is nearly identical in mathematical structure to quantum electrodynamics (QED) and to the unified theory of weak and electromagnetic interactions advanced by American physicist Steven Weinberg and Pakistani physicist Abdus Salam .

[kallubhai4u]

Ok kallubhai4u-ji,

Let me try and rephrase my query. 
A ) Could you tell me how gravity affects light ??  Newton's law says that the two itneracting bodies should have masses to have gravitational effect on each other.  Does photon have mass ? If so, is it calculated by Einstein's equation?

B ) Apart from the deflection of light from it original path under the influence of gravity, do photons also get accelerated under the influence of gravity ??  Is it possible to measure what is the spatial deflection and by how much were the photons accelerated ?

I'll try and break down my queries further if you find that I'm asking too many questions at a time.

Thanks,
Vivek

hi visu, u can call me by my name i.e. Kalyan, well i've got something 4 u. read & get blasted by physics.

Light is not affected by Gravity and neither is matter. This is because "Gravity" is what happens when the matter curves spacetime. There is no such thing as "action at a distance". This is because the force of Gravity is a "fiction". The way things move in spacetime is a direct result of the curvature of spacetime just where you are. It is feeling the "local slope" of spacetime and rolls down the "hill". There is a "propagating" part of it, which travels at the speed of light.

Mass tells space how to curve and space tells matter how to move.

Therefore you don't even need a mass to be affected by "Gravity" because it is your "so called" particle responding to the local curvature of spacetime. It doesn't need to curve spacetime itself to be affected by "Gravity". It will still "fall" or "propagate" along the geodesic which is definitely NOT a straight line (if there are any mass sources out there) it is the straightest line (minimum energy) that can be drawn depending on the other kinematic constraints.

Special Relativity insists that you consider spacetime without the sullying effects of mass but they (mass sources) are there and need incorporation in the overall picture if you want to make sense of it all.

There is an extension of this with electromagnetism also curving space but not according to the mass (because it has no rest mass) but according to the static or dynamic electric and magnetic fields. This actually tells particles how to move as well. Just bring two magnets near to each other and watch the "sparks".

Now I know there are "particles" that connect source and destination (photons) and these are the bosons (exchange particles) that we have to connect these events. There are so called "gravitons" that also connect source and destination which people want to ascribe to gravity. But like virtual photons these should be virtual gravitons too. This seems to be where the confusion seems to overtake everyone. Let me suggest the answer....

Everything to do with "propagation" are “wave properties”. This is true for particles too since so called "particles" propagate as waves too. There is nothing "particulate" about propagation. Propagation does not exhibit any particle properties.

Everything to do with “interactions” are "particles". When two entities interact then it will be as "so called" “particles”. Never the twain shall meet. That is where you have wave particle duality. Though “things” can exhibit this “stuff” at the same time they are not the same thing identically, and experiment shows this is true.

There are only travelling waves not travelling particles. And there is no interaction between waves only interactions between particles. It just so happens that those thingummyjigs you want to call particles are self-consistent non-spreading packets of waves and they move as waves. The occasionally interact with other similar entities and this is an "interaction" that is what the standard model is all about. It tells you about all those lovely interactions. I think that some Physicists take things beyond what is shown by experiment and they sometimes become confused and think they are the same things. They are definitely not. There are locality coincident phenomena that seem to say that they are “close”, just accept that this is what is happening.

If I throw a ball to you may think it is a quantum particle it is not. It is a complex series of inter-particle interactions combined with a collective propagation as a wave across the intervening space on a geodesic path. Get this straight and you start to enter a bigger world and you will start to understand what all this is really about. Gravity (and light) is about "propagation" and it affects spacetime and you can have curved spacetime and you can have ripples in spacetime. The differences between gravity and electromagnetism is in the symmetry of those separate phenomena (symmetric vs. anti-symmetric). They both affect the only "medium" there is... "spacetime" and it can be curved and warped by the different types of waves buzzing around. Remember it is not a material medium but a "system".

Photons while they are propagating can not be seen. To see a photon you must scatter it that is an interaction. They interact as a "particle" but propagate as waves. It is simple and all experiments tell us this is so just accept it and stop inventing stuff to clutter your minds. Interactions occur at or very near the particle and are "local" events (two or more particles interact). That is the stuff that shows that wonderful symmetry. There is symmetry in propagation but it is of another order. Please keep them in different pigeonholes.

Like someone in another post said you can take analogies too far and one analogy is the Feynman Diagram. It shows both propagation and interactions as apparently the same things they are not. They are great tools but there are limits.

After thought: I hope you remember when an interaction occurs, the superposition of those quantum wave states collapses to one final state. When that collapse occurs the information being collapsed is coming from it "totality" which is an "semi-infinite" extended waveform in spacetime and it's dynamic interactions with it's entire "system", so it is no wonder it carries information from other parts of your experiment and from "entangled" parts of "itself" where ever they may be. The other point to note about propagation is that while a packet travels at usually less than the speed of light the component wavelets are propagating at the speed of light even for de Broglie waves. Please think about that.

i got this info frm http://forum.physorg.com/index.php?showtopic=1195&st=15. u can join there too as i m gonna do soon.

[shivani]

Kalyan : ) I am yet to go through all the posts out there, and so cannot comment. As far as a post on QCD , seems you have already done that, and I would not have been able to contribute much anyways.
Here are a few more unanswered ones that no one has attempted so far.
Bibha's set
1. Is microwave radiation (observed by Penzias & Wilson as well as COBE) the only experimental evidence for Big Bang ?

2. How can Friedmann’s third model be extrapolated to state the universe to be flat ?

3.“The mass of the sun curves space-time in such a way that although the earth follows a straight path in four-dimensional space-time, it appears to us to move along a circular orbit in three-dimensional space.”. Yeh kuch samjha nahiin. Any visual analogies ?

4. Can you give an example of a particle with a spin=1/2 (no, not an electron ), i.e., one that requires a 720 degree rotation to look identical ?. Matlab, the way Hawking uses a dot for s=0, an arrow for s=1 and double-headed arrow for spin=2.

Might be able to put a post on 3rd one.. (if I dont get too lazy again!!)
One more from Visu
Is there an order to planetary arrangement, in terms of the distance between a planet and its sun ??

And thanks for the link. Would try to go through it.

[Mandrake]

This is a quick post, so will only reply to reasonably understood points.

Here I refer to the 3rd point in Shivani's post.

If I were to build an extreeeemely straight road and ask you to drive a car that can only go in one direction, you'll keep going forward till you reach the point where you started.
Obviously, the road was straight, and you were anyways unable to turn anywhere else. The reason you ended up at the starting point is because the road was built on the sphere that the earth is.
So, to you, you are going in a straight line all the time. But to an observer in space, you are going around in a circular orbit...

Ditto, The earth was travelling in a straight line, but it's path is inside the depression caused by the sun's gravity. So, it is still staying true to it's straight path, but the path itself is along a curved space-fabric.

The other point is Vivek's question, as I understand it, is, "Is there an order to planetary arrangement, in terms of the distance between a planet and its sun ??" (quoted from Shivani's post above)

The planet-orbits are in a mathematically progressive state. The real figures I do not remember by heart, but can produce them later.

In fact, it was this 'order' that got the early astronomers thinking. Apart from the obvious order, they also realized that the gap between Mars and Jupiter was exactly double as compared to other successive orbits.

And, exactly in the orbit where there should have been another planet, are the asteroids. This has often led to the speculation that there was a planet there which must have disintegrated...

Also, the other order is: Mercury, Venus, Earth and Mars (and perhaps, 'that' planet) are all rocky planets.
Jupiter and Saturn are gas-planets.
Uranus, Neptune and Pluto are ice-planets.

[kallubhai4u]

this is an attempt to answer the third question Shivani had posted.

The Big Bang Theory

Representation of the universe according to inflationary cosmology.
The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.
In 1927, the Belgian priest Georges Lemaître was the first to propose that the universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant nebulas by astronomers to a model of the universe based on relativity. Years later, Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.

The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.

Although the Big Bang Theory is widely accepted, it probably will never be proved; consequentially, leaving a number of tough, unanswered questions.

[shivani]

Thx Mj
And since people are on Answering spree, I would post one more topic, and if someone has material on it already please post.

Why is movement in time unidirectional and why can one not move backwards? I understand that while statellites and launched the time has to be adjusted ahead slightly as they are moving faster ( according to relativity.. still trying to understand that part), but no calculation is applicable to move back in time...why?

[shivani]

this is an attempt to answer the third question Shivani had posted.

The Big Bang Theory

Representation of the universe according to inflationary cosmology.
The Big Bang Theory is the dominant scientific theory about the origin of the universe. According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.
In 1927, the Belgian priest Georges Lemaître was the first to propose that the universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant nebulas by astronomers to a model of the universe based on relativity. Years later, Edwin Hubble found experimental evidence to help justify Lemaître's theory. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.

The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.

Although the Big Bang Theory is widely accepted, it probably will never be proved; consequentially, leaving a number of tough, unanswered questions.

I am sorry Kalyan, but I did not get this explanation. Do you wish to bring about following two observations here?

1. Earth moves in its orbit around the Sun in a circular motion in our solar system.
2. The whole solar system is expanding and moving out is seemingly straight direction so actualy earth is moving in a straight line as well?

[YaarMere]

My compliments to you bunch of Stephen Hawkings Science is fascinating I tell you. Hard too!

[shivani]

Beg to disagree YM .. it is simple. only we keep trying to complicate it : ). Would also appreciate if you take active participation in thread.