Cosmology

Top five misconception you probably have about expanding universe .

In previous article ( what is expanding universe and what it means ), you learnt the concept of behind it and  you got to know how Edwin discovered  it . You  also got to know how expanding universe does rise to ultimate fate of universe . Edwin noted the receding speed of faraway galaxies from us is proportion to separation between it . You might say you have understood everything about “expanding universe ” but dear readers , things are not clear here completely . The word “expanding ” itself a big misconception in itself.  There are the lot of misconception regarding this concept. Most people have misunderstood it . It is crucial to correct those misconception . So I have listed five things that you probably don’t know or you have understood in wrong way .

1) Universe is not expanding .

As I told you above ,the word “expanding ” itself a misconception . Universe is not expanding but it is stretching like stretching of  rubber band . ‘Expanding’ and ‘stretching’ are two different term . Let’s understand this with analogy . Suppose two balls are at few distance apart from each other on solid surface of Earth . If you try to move one ball away from other , the distance increases between balls , we call it expansion of ball because ball is really moving on stationary surface . Now let’s suppose , there are two points on rubber band . If you pull apart rubber by applying force , that means you are stretching rubber , here we should be noted that points are not moving but only surface at which points lie are stretching . Let’s understand analogy in three dimension. It might be raisin loaf baking in oven where each raisin represents galaxies , as the loaf expands , distance between all raisins increase .

Loaf with raisins , distance between raisins are increasing .
You can see bread is expanding , so distance between raisins also increase . There is not actual movement of raisin but only loaf is expanding . Each raisins can be represented as galaxies . That expansion is called Hubble expansion .

We get two different pictures in our mind . In one , surface is stationary but in other , surface is moving apart or “stretching ” . The same ‘stretching concept’ applies in space . All points in universe such as galaxies  are not moving through space but space at which these galaxies lie are stretching . Space is not static but it is dynamic in nature . It can be warped or  stretched .You saw in rubber band analogy that you are applying external force to stretch the rubber band , but in universe , that external force becomes dark energy .

2) Universe is moving faster than speed of light . 

Yes you read right .Universe is moving faster than speed of light . In other words , receding  speed of any faraway galaxy from us can be more than speed of light .  As we know that universe is expanding or stretching at rate of 68 km per second per megaparsec . 1 megaparsec is equal  to 3.26 million light years and it is unit of distance . That means any galaxy  which is at 1 megaparsec away from us , is moving at rate of 68km/sec . Any galaxy which is 10 megaparsecs away from us , is moving at speed of 680 km/sec . But what about any galaxy which is 10000 megaparsecs faraway from us , yes , its recession speed would be 680000 km/sec . Now it is much more than speed of light . But it does not violate postulate of special theory of relativity which states that nothing can move faster than speed of light . It doesn’t apply here , because here , actual things are not moving but only space is stretching .

3) Universe is not expanding into anything – 

This is another misconception that most people have . Most people argue that if universe is expanding then it must anything which is beyond universe . But dear readers , space is not expanding into anything but it itself expanding . Universe doesn’t have boundary . Universe is either infinitely big or finite curve at any point . If universe is curve then there is no way to escape outside and space is curved so that if you could travel billions of light years in a straight line you would eventually finish back where you started. Nothing can affect us from outside of universe , we will never know what is outside of universe and into what universe is expanding . But if the universe is infinitely big , then it is meaningless to ask what is outside because adding infinity to infinity is always infinity.

4) Universe doesn’t have centre .

People usually argue that if universe is moving or expanding than it must have centre or expansion of universe must be started from centre of universe . But this is another big misconception . If you followed me  up to  here  , then you can easily say that universe have neither edge nor centre .  There are infinite points in space ( such as galaxies ) . To verify expansion of universe . We need to measure distance between two points which is increasing at faster rate . If we go back in time , we will see distances between any pair points are nearer than now . If we continue to go much back in time , we will eventually reach at point where distances between any pair points become zero . That specific point is called singularity of big bang . So we can say all points in space were once a part of singularity of big bang . There was only expansion of space or more clearly , stretching of space but not actual movement of matter through space. Hence expansion started from  nowhere and there is no centre of entire universe .

5) Expanding universe is not a local effect . 

You might have  doubt here that if universe is expanding then why do not moon and sun  moving away from us ? .

So let me clear you that expansion of universe is not a local effect . It can only be tested  for  a galaxy which is much farther than us . Why does it so ?

Spacetime can be stretched like rubber sheet
Spacetime continuum

Answer is that expansion  causes by some mysterious force called “dark energy ” which stretches the space apart . But this force is too faint to overcome local gravitational attraction for now .But our future is terrible . If universe continues to expand , these mysterious “dark energy ” will become  so much extensive that it can overcome local gravitational attraction between bodies or even inter molecular attraction , so all molecules and atoms will get expand and universe will die forever.

I tried my best to correct these common misconceptions . If you have doubt , you can send us mail . Don’t forget to comment below

 

I am science enthusiast and I love to write blogs for students and youths who love science. I have deep interest in astronomy and cosmology. I believe that science is most effective tool to serve humankind.

.

2 COMMENTS

  1. Good concepts…now I can say that I have understood everything about expanding universe . Great post . Great clarity . Thanks for sharing

Comments are closed.

I am science enthusiast and I love to write blogs for students and youths who love science. I have deep interest in astronomy and cosmology. I believe that science is most effective tool to serve humankind. .