Ever wondered that we can remember past but, are unable to do so for future. Why we perceive the time’s arrow moving only in one direction that is from past to future and not the other way round? The answer to this could be explained by entropy of a closed system. But, before we get into into the answer, we should know a little about notions of time. According to Stephen Hawking, there are three notions or arrows of time: psychological (that we perceive through brain), entropic (movement in nature from order to disorder) and cosmological (it moves forward or backward depending upon the inflationary or deflationary state of the universe). Psychological and entropic arrows of time could be considered same and here we are discussing the reason that forbids us from remembering future in the context of psychological and entropic notions of time.
In a closed system, changes take place in a direction that increases entropy. Now, what is entropy? In simple language, we can say that entropy is the degree of unpredictability of a system. In case of Universe, we are on a constant move that is increasing the entropy or disorganisation within it. It is the reason behind the flow of heat from a hot to cold object but, not vice versa. Our memory is created by the particular fashion in which neurons orient themselves within our brain, energy is required to create this orientation which in turn heats up our bodies, thus increasing the entropy. So, the reason behind our perception of uni-directional psychological notion of time is that it creates increase in entropy.
Read more on it: http://www.math.cornell.edu/~numb3rs/luthy3/thearrowoftime.html
In 1960, when for the first time earth’s global gravity was charted then it was noted that certain regions of earth have lower gravity than others. Regions of Canada, particularly Hudson Bay area have remarkably low gravity compared to other parts of the world. Initially, it appeared to be a mystery but, now there are more than one explanation for the presence of low gravity in that region.
Hudson Bay with Canadian bordering states. by Rishabh Tatiraju
How is gravity created?
Gravity is directly promotional to mass of a body so, in other words mass creates gravity. The shape of earth is not even, it bulges out near equator and gets flatter near poles. Regions of earth with lower masses have lower gravity compared to regions having higher masses. So, do the Hudson Bay area have lower land mass compared to other parts of Earth? Yes, but why? In case of Hudson Bay area, it could be explained by two factors, which are explained below:
Convection in Earth’s mantle
The mantle of earth consists of molten rocks known as magma, magma is in constant movement creating convection currents. These convection currents pull the continental land masses toward them and there by decreases the land mass of the area that is getting pulled. Convection currents are not always same at an area and keep on shifting from place to place bringing on various geographical changes too along with its movements.
Rebound effect of ice sheet
Around two miles thick ice sheet known as Laurentide Ice Sheet existed in the area which is now Hudson Bay area. This ice sheet was extremely heavy and had weighed down the area of earth where it existed. It started melting due to rising temperature of earth and disappeared completely around 10,000 years ago but, had left an indentation in that area. The indentation has pushed land masses towards the sides and created a low land mass in the central area which has resulted in lower than usual gravity in this area.