What is negative Energy/Exotic Energy? So I have been researching around a little as I am highly interested in Astrophysics and I came across an energy I have never heard of before; negative energy also commonly known as exotic energy. Now I started to research this however I found the concept rather hard to grasp due to a simple lack on information around on the Internet.
Could somebody kindly explain (if possible using real life analogies) what exactly negative energy is or at least the whole concept/theory behind it.
 A: Exotic energy is not really definable and is more or less generic but however I will elaborate, exotic matter\energy is any object or entity which is not either present at our current knowledge or is an hypothetical and not proven scientifically or is rare to discover or maybe unfortunately can never exist and will remain our dreams. To be honest I could even consider anti-matter to be exotic as it's not commonly encountered. 
It's too generic to be given an set-solid definition for. 
Negative energy\mass is again hypothetical as there are no proof of existence of such energy or mass thus is considered exotic. Nevertheless, let me elaborate on its effects and its hypothetical behavior. 
Einstein describes all mass with positive value will "press" down upon fabric of space-time however "negative" shows all of the Negative mass to have negative mass (as straightforward as it sounds...) this means it should do an opposite as creating gravity - Negative gravity so unlike pulling it will push mass away from its space so that's one behavior of negative mass.
So in other words its like anti-gravity and due to this property its an ideal material for development of hyper-crafts and other sci-fi based technologies. However since its not or has been observed in space nor on an laboratory it still remains in the sci-fi category.
Final words, mathematics permits all kinds of unreal actions taking place such as being able to travel faster than $c$ (speed of light) however in physics they need to proven and tested therefore many physics concepts may be eligible and logically sensible in the beautiful language of mathematics but reality may not permit these things, therefore these may objects proven in mathematics and may never co-exist in our universe. 
A: Negative energy is a quite different than Anti-matter. If you collide Anti-matter with regular matter you get a result with positive energy (Gamma rays). If you were to collide Negative energy and matter you would get nothing. It has negative mass (Anti-matter has a positive mass.) It is a hot topic in physics as it allows the creation of (Warp drives, Traversable Wormholes, Time machines, etc.) 
A good analogy is money. 
The amount of money in a bank account is the amount of energy. Negative energy would be like having a deficit of money in a bank account.
A: Negative energy occurs when the energy level for a given space is below that which is considered zero energy. A zero energy space is not really zero but is always full of some virtual particles popping in and out of existence. 
A: In general relativity, the energy content of a region is given in terms of a stress-energy tensor. The elements of this tensor are not given by general relativity itself and can differ depending on what matter and fields are present. To try to draw general conclusions about what is allowed and forbidden in general relativity, physicists have tried to place restrictions called energy conditions on the properties of the stress-energy tensor. These energy conditions take the form of requiring certain quantities derived from the stress energy tensor to be positive since such restrictions forbid things like the existence of singularities outside black holes, the non-existence of traversable wormholes and that sort of thing. Fields and matter that violate such restrictions are said to have negative energy. There are lots of subtle mathematical results on the extent to which violations of the energy conditions might be possible. See
http://arxiv.org/abs/1302.2859
http://arxiv.org/abs/gr-qc/0205066
and references therein.
