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# Tag Archives: relativity

## Superman, Time Travel, Relativity and confusion!

In the original **Superman** movie, Superman flies around the world opposite its rotation at a speed faster than light (or close o it) and witnesses time running backwards. But at such speed, time would slow down for Superman, but not stop, and certainly not move backwards, would it? Instead of seeing people and events moving backwards and undoing themselves, wouldn’t everything on Earth appear to simply stop moving to Superman?

(Cybele Cotter asked)

Answer:

It was a common belief among the fans of relativity that – ” if any object travelled with the speed of light, then time would stop for him and if he traveled faster, he would go back in time.”

But, there is some tweaks required somewhere which we strongly expect to take place in the near future which would remove the absurdity in theory and practice.

“**Superman**” is fiction and was considered a person who can go back in time. This was not based on relativity. But, based on the results of relativity, we tried to believe that such a thing is possible if we could travel that fast.

When Superman goes back in time, He going to that past and correcting some mistakes happened in the past. Such a thing is practically impossible with the present technologies and techniques.

## M – Theory, String Theory and more

Nijisha’s Question: There are various forces we see in nature, and among them, gravitational force is the weakest. If we think about it ,the entire earth is pulling on us and yet we can manage to pick thinks up. I’ve heard somewhere that we can explain this weakness of gravitational force with the help of extra dimensions ( Something related to M theory? ). Can you explain this theory ?

**Ans**:

It’s a little bit difficult to discuss in detail the M theory in detail as such at School level. However, I’ll try to give a brief idea about it.

**M-theory** is an extension of string theory in which **11 dimensions** are identified. This is a theory currently in development

To quote from Wikipedia:

“In the 1980s, a new mathematical model of theoretical physics called string theory emerged. It showed how all the particles, and all of the forms of energy in the universe, could be constructed by hypothetical one-dimensional “strings,” infinitely small building-blocks that have only the dimension of length, but not height or width. Further, string theory suggested that the universe is made up of multiple dimensions. We are familiar with height, width, and length as three dimensional space, and time gives a total of four observable dimensions. However, string theories initially supported the possibility of ten dimensions—the remaining 6 of which we can’t detect directly. This was later increased to 11 dimensions based on various interpretations of the ten dimensional theory”

In **M-theory** may stand for membrane. (Some claim M for mother, matrix,mystery etc)

M-Theory brought all of the string theories together. It did this by asserting that strings are really 1-dimensional slices of a 2-dimensional membrane vibrating in 11-dimensional space.

Though M – Theory is developed mathematically, it is not proved physically. Scientists and Mathematicians take M-Theory as the only theory developed so far which can explain all the aspects of Universe (or multiverse) as a whole. But, I am sure, new theories will come and take over as we develop our understanding further.

**Stephen Hawking’s** New work **The Grand Design** talks about the **Multiverse** and the God’s intervention in the creation of Universe (which he says not necessary)

Ref:

(* I fear that I’ve brought more unknowns in explaining the one unknown. However, it will be good if the discussion goes on*.)

## Nature of light, relativity and blackholes

Prasanna asked:

we know light has got dual nature. & blackholes has got enormous gravity from which even light cant escape. how can gravity can influence a mass less stream of particles like gravity?

Ans:

Do you know why solar eclipse is watched with great importance by the scientific community?

OK

Einstein’s theory of General Relativity was proved right(?) when bending of light by masses was observed in reality.

Please go through the links below and hope that you’ll find an answer there.

## More on Cosmological constant

A constant introduced by Einstein (1917) into the equations of general relativity to allow a steady state cosmological solution to the Einstein field equations. The constant was introduced before the concept of the Big Bang had been conceived, so an expanding or contracting universe was regarded as physically implausible, leading Einstein to add as a "fudge factor." In theory, the constant can be derived from quantum field theory, but the derivation has not yet been performed. Einstein’s cosmological constant is equivalent to a vacuum energy density, which means it can be put on the left hand side of Einstein’s equations with the geometry (as Einstein did), or on the right hand side with the stress-energy, both forms being mathematically equivalent.

The value of in our present universe is not known, and may be zero, although there is some evidence for a nonzero value; a precise determination of this number will be one of the primary goals of observational cosmology in the near future.

The value of the cosmological constant is an empirical issue which will ultimately be settled by observation; meanwhile, physicists would like to develop an understanding of why the energy density of the vacuum has this value, whether it is zero or not. There are many effects which contribute to the total vacuum energy,

including the potential energy of scalar fields and the energy in “vacuum fluctuations” as predicted by quantum mechanics, as well as any fundamental cosmological constant.

If the recent observational suggestions of a nonzero are confirmed, we will be faced with the additional task of inventing a theory which sets the vacuum energy to a very small value without setting it precisely to zero. In this case we may distinguish between a “true” vacuum which would be the state of lowest possible energy which simply happens to be nonzero, and a “false” vacuum, which would be a metastable state different from the actual state of lowest energy (which might well have = 0). Such a state could eventually decay into the true vacuum, although its lifetime could be much larger than the current age of the universe. A

final possibility is that the vacuum energy is changing with time — a dynamical cosmological “constant”. This alternative, which is sometimes called “quintessence”, would also be compatible with a true vacuum energy which was ultimately zero, although it appears to require a certain amount of fine-tuning to make it work.

No matter which of these possibilities, if any, is true, the ramifications of an accelerating universe for fundamental physics would be truly profound.

Read More at

## Time Travel, Relativity

I’ve just watched “Faster than the speed of light” programme on ITV. There is one assumption that these people always have that I have never understood. Why does travelling faster than the speed of light have to mean “time travel”??. The only reasoning i ever hear is that “You would arrive before you left”. This just doesn’t make sense to me. Why is light any different to sound? In theory, you can make a sound then travel faster than the speed of sound to hear your own voice in another location.

If they mean Einstein’s theory about time slowing down as you reach the speed of light, why not say that? Why state that “it’s impossible to go faster because you “would arrive before you departed”? Do you know what I mean??

Thanks

Russell

Answer:

According to Einstein’s assumptions in the theory of relativity, the velocity of light in vacuum is a constant and no particle can travel faster than light. The theory of relativity is based on this central concept. So, if we imagine to travel faster than light, time will reverse (As per theoretical results) and we may go back in time. That is why travel with or above the speed of light is referred to as “Time Travel”.

Light is an electromagnetic wave and is different from sound as it is a mechanical wave which requires a medium to travel. Sound cannot travel through vacuum.

## Was Einstein Wrong?

**Was Einstein Wrong? What is the neutrino particle which traveled faster than light?**

Answer:

As we know it now; **Neutrino** is a neutral subatomic particle with a mass close to zero and half-integral spin, * rarely reacting with normal matter*.

Three types of neutrinos are known –

Einstein’s theory of relativity suggested that no particle can travel faster than light in vacuum.

If neutrino travels, there is something wrong and we have to make necessary amendments

**Further Reference**