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The weakness of gravity

The story goes that a young Newton was sitting beneath a tree when an apple fell to the ground, which he famously attributed to a force of attraction between the apple and the Earth called gravity. He went one step further to suggest that it is the same force that is responsible for the orbits of the moon around the Earth and the Earth around the Sun.

Whereas the story is most likely fictional, it illustrates an important concept that ideas are borne out of curiosity. Learning to ask the right questions is one of the cornerstones of scientific advancement. The lack thereof, I believe, has played a fundamental role in scientific decline in the Muslim world (as I’ve previously discussed here).

One of such questions and indeed one of the biggest unsolved mysteries in our understanding of the Universe is; why is gravity so much weaker than the other forces of nature? It is questions like this that the Large Hadron Collider, the most powerful particle accelerator in the world, is designed to solve. This particular curiosity is also one of my primary research preoccupations and the reason for my somewhat long hiatus from the blogosphere.

Our current understanding of the Universe is embodied in a theoretical framework called the Standard Model. The theory describes the fundamental particles and their interactions with each other via four forces, the weakest of which is gravity. The weakness of gravity may come as a surprise since we hold gravity responsible for the Moon orbiting around the Earth, the Earth around the Sun, the motion of the galaxies and the fact that we’re not floating in space. However, it is actually extraordinarily weak compared to the other forces in nature.

 How weak is gravity? It takes the entire mass of the Earth to pull that apple to the ground! The force of gravity becomes stronger the more mass objects have and the closer they are to each other. Its effects only become visible when we talk about objects as large as the Earth and are virtually unnoticeable if you consider for instance, the gravitational attraction between the individual apples on the tree.

So, what makes gravity so much weaker than all the other forces?

In 1998, Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali proposed the scenario of Large Extra Dimensions to solve this puzzle. The basic idea is that there are more dimensions in space than the three-dimensions that we live in and experience.

How does this explain why gravity is so weak? While the other forces of nature are constrained to our three-dimensional world, gravity is thought to be free to propagate in these extra dimensions, so its effect in our three-dimensional world is somewhat diluted. Hence we see it as being weak since it is thinly spread over all the dimensions, whereas its strength is probably comparable to the other forces.

It is proposed that these extra dimensions are un-observably small, since we don’t witness objects vanishing into these higher dimensions and that they are compactified, for instance they may be tightly curled in a loop, such that even if you enter one of these dimensions, you won’t get very far and end up right where you started.

At the Large Hadron Collider experiment at CERN, often referred to as the ‘Big Bang machine’, we accelerate bunches of protons in opposite directions around a 27 km ring and then collide them head-on. The collision produces an immense amount of energy that can create new particles. One of these could be the graviton, the particle thought to be responsible for transmitting the gravitational force. If gravity permeates through all of the extra dimensions, there may be times when graviton is produced in these high energy collisions and then escapes immediately into these other dimensions.

This disappearing act of the graviton would therefore be a tell-tale sign of the existence of extra dimensions and would produce an imbalance of energy in our detectors as the energy of the graviton would be ‘missing’.

We searched through scores of proton-proton collisions to find cases where a graviton may have been produced and then vanished immediately into these higher dimensions. So far, with the data available at the end of 2010, we have not found any evidence for these particles and as a result we were able to place constraints on the size and the number of these extra dimensions.

However, so far in 2011 we have accumulated 30 times more data than was available in 2010. With so many proton-proton collisions at the highest energies ever achieved, the likelihood of a scientific breakthrough has increased tremendously. Who knows what we may discover and what Pandora’s Box it might open. The beauty of science is that there will always be one more question to answer.

Dr Sarah Alam Malik is a postdoctoral associate in Particle Physics. She works on the Large Hadron Collider experiment at CERN, Switzerland and the Tevatron experiment at the Fermi National Accelerator Laboratory, USA. Her research interests can be found here.


The views expressed by this blogger and in the following reader comments do not necessarily reflect the views and policies of the Dawn Media Group.

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Comments (22) Closed

Jul 14, 2011 11:55am
How cool would it have been to have worked at the LHC!!!
Jul 14, 2011 12:02pm
Finally, some real science in the DAWN Blog!:)
M. Asghar
Jul 14, 2011 12:25pm
The poor "good" machine LHC at CERN in Geneva, Switzerland, is expected to answar so many questions from cosmology to the only presence of matter without the corresponding antimatter in our universe and how this mass of the matter is created (elusive Higgs boson? ).
Jul 14, 2011 12:39pm
It's a matter of pride that one of Pakistanis work at CERN. Please keep us updated on achievements of Big Science through Dawn. Although we tend to believe that all truths have once for all been revealed in scriptures (Like sun sets in west mud, earth has ends, age difference between earth and Universe cannot be more than six days) but it is interesting to to get info from mere human resources too.
Jul 14, 2011 12:41pm
Michio Kaku and Brian Cox were the first guys that kindled my interest in this twisted world through horizon series. Pretty epic stuff although being a layman (though I work a bit with electromagnetics but that's not good enough), this concept of lost energy always bewilders me. And if that's not enough, there comes the theory of everything! Fascinating it may be, don't you think that by calling it 'everything' we are somehow capping our imagination and other mysteries that lie beyond the four forces are somehow being ignored? True that we haven't observed any of those but hey..'theory of everything' is a pretty big statement.
K. M. Nawaz
Jul 14, 2011 02:13pm
Dear Dr. Sarah, I am really pleased to known that you are involved in CERN. You might be an expert; but as far I know, the experimentation at CERN was to find the Higgs Particle; the particle which is supposed to give mass to atom. This particle is supposed to have provided mass to the Universe at the time of Big Bang and therefore is also known as GOD's particle. I remember reading that the scientists there did locate this particle which has a life of less then a millisecond. One can surely argue that mass is responsible for gravity, and thus your write-up could thus be interpreted. I believe that gravity has its own dimensions too. What I feel important to stress is that all research and all knowledge is purely HUMAN. It belongs to all humanity at large and there can be no Islamic, Christian, Jewish or Hindu contribution. Unless we drop this thought process, we will not get into the mindset of acquiring knowldge which may not be in confirmity to our religious thoughts. Just to remind you that EVOLUTION is not taught as a source of knowledge in our schools and higher educational institutions.
Sifwat Ali
Jul 14, 2011 03:40pm
The article is breath of fresh air although I disagree with the remark about Muslims. I worked on the space shuttle project in the late 70’s and early 80’s and a few of us “Muslims” were at very high levels in the Apollo program here in the US. I think it has more to do with the funding levels of science in Pakistan as well as other things such as education and healthcare.
Pandit Ram Tirath Sh
Jul 14, 2011 03:50pm
The types of particles that exist in the universe would depend on the temperature. At high temperatures, particles have so much energy that whenever they collide many different particle/ anti particle pairs would be produced. Although , some of these particles would annihilate on hitting antiparticles. At the precise moment of Big Bang ( moment of creation), the universe is thought to have had zero size and so to have been infinitely hot. But as the universe expanded , the temperature of the radiation decreased along with the force of garvity because of the ever expanding universe. This cycle of expansion and contraction of the universe will go on forever till God intervenes.
M. S. Malik
Jul 14, 2011 05:49pm
forgive my ignorance but I want to ask that If Graviton is responsible for the transmission of gravity then it needs to be traveling definitely more than speed of light (because change in gravity is felt or in other words "transmitted" much faster than speed of light) and for that sake it needs to be having infinite mass and hence infinite energy requirement to move or simply it needs to infringe the theory of relativity. What is the justification of research about Graviton then?
Jul 14, 2011 06:20pm
Dear Dr. Sarah I am extremely pleased to see that you are working in one of the most esteemed scientific experimental project on earth today, trying to unlock the mysteries of the universe. And trying to answer the most fundamental of all questions. However in the current article the question you have raised is 'How is gravity so weak’? [I am not an expert in this area, so please excuse me]. But in my opinion Gravity can be one of the most powerful forces working in the universe. When it comes to black holes we can observe gravity in its extreme. The gravitational pull exerted by the black hole (which forms as a result of a supernova, death of a star) is so immense that even light cannot escape it. In other example it is the gravitational force that exerts such immense pressures inside the stars to causes fusion (offcourse the ultra high temperature in the core of the stars is also a contributing factor). So my question is 'how do you justify saying Gravity is so weak'? Thanks
Jul 14, 2011 06:28pm
Too Good a reply.. "sun sets in west mud, earth has ends, age difference between earth and Universe cannot be more than six days" Superlike
Jul 15, 2011 01:59am
There is still no good definition of gravity, and Einstein's definition of gravity as a dent in the fabric of space (space-time continuium) is perhaps all we have for now. Until we can define it, perhaps we cannot really understand it.
PE Harvey
Jul 15, 2011 03:44am
Maybe you could revisit Einstein's idea of a 3D space curved ( a fourth dimension, not time) by mass. There are no opposite charges attracting each other, as in electro-magnetism. Curved space makes sense.
Jul 15, 2011 07:44am
My dream work but my weakness in grade 12 math (wish has a better teacher) and pressure from parents made me engineer instead of phycist. Not sure how many scientist we have killed in south asia. Now I am stuck to google to get all information on universe and read about it a lot and if I get sometime then try to watch video on PBS website and if lucky watch it on TV(though difficult with no one else in house having such interest)
Jul 15, 2011 12:14pm
Hi ! It would be great if you could write a book explaining , in layman's terminology , the evolution of physics over the past 1000 years. The nature of 'matter' has always been of great interest to philosophers and scientists alike and it would be great to have
Jul 15, 2011 12:16pm
Hi ! Can you write a book about the evolution of particle physics? The nature of 'matter' has been of great interest to philosophers and scientists alike for a long time . It would be really great to have a comprehensive book written by a Pakistani scientist on the subject! Rehan It would be great if you could write a book explaining , in layman's terminology , the evolution of physics over the past 1000 years. The nature of 'matter' has always been of great interest to philosophers and scientists alike and it would be great to have a Paki
Jul 15, 2011 02:42pm
The writer has very weak knowledge of physics from start to end he whatever he written is not correct. First- Gravity is not a weak force is strongest force in universe( responsible for all cosmic mechanism) Second- The dimensions beyond three dimensional system (Space time) is first proposed by Sir A. Einstein Three- Einstein theory suggest the gravitation is not a force (& he ends Newton's gravitation system as its a special case of general relativity its not valid in each frame of speed), its juss a effect of destruction of space-time. The writer even don't know about this he becos he didn't mention about this( it should be must mention if discussing the most correct theory of Gravity) Four- Every thing belong to our universe is present in this space-time (4 dimensional system). Article mentioning superdimention like magical world & saying most system can interacts in only 3 dimensions except few.
Jul 15, 2011 09:20pm
I hate to be critical of a fellow poster but in one sentence I can disprove your posit that gravity is the strongest force. Do you not stand on the ground with the entire force of gravity of the earth pulling you down? What stops you from being pulled further towards the center of the earth is the electro-magnetic force interacting between the atoms beneath your feet.
Jul 19, 2011 11:57pm
I don't understand how people can find this blog and then go on to ask a question like "How can you say gravity is weak?". Gravity is the weakest force by FAR. Look at the amount of energy is released when you split an atom apart (nuclear bomb), then compare that to seperating rocks from a pile of rocks (not very energetic).
Jul 20, 2011 06:38am
beauty! well said.
Jul 20, 2011 05:03pm
Dear Frnd, Never compare mass with charge. These are two diferent quantities & standard maths never allow. gavity (or electric force intensity) is depends on the density of metter (m/r2 or q/r2, if u are on surface). But in nature the mass is quantity wich can be concentrated (to infinity not charges). U can see a no. of curious case of blackholes.. where the gravity is show high even it not allow light to scape....but u never find a force is so stroge in nature who can do this thing except gravity... never compare gravity..(u can compare earth's gravity but not black holes gravity....)
Jul 20, 2011 05:18pm
it really a nice example to counter argument (n I ever seen such nice example of elc-mgnto force) but my dear frnd if u read the article u will find here we are discussing about gravity & not earth's gravity...& if u try to hold up urself on blackhole u will collapse suddendly & ur elcto-mgnto force will coundn't help u........