Until the middle of the 20th Century the major advances in science were concerned with matter and energy.
Since then the science of information has been growing in importance as we learn more and more about different kinds of natural and man-made information-processing systems.
In particular, we have discovered that in addition to physical machines like windmills, steam engines, electric motors, generators, and pottery kilns which (mostly) manipulate matter and energy there are also abstract machines that process information. These are called virtual machines, like the operating system that controls your computer or the spelling checker that finds and fixes mistakes in your essays.
If you open the computer and look inside, using microscopes, voltmeters, and other devices found in physics and chemistry labs, you will not discover an operating system or a spelling checker, because operating systems and spelling checkers are not physical or chemical machines, but virtual or abstract machines. Nevertheless they exist when the computer is working and they perform real functions. They exist as a result of very complex patterns of activity in the physical components. Describing those patterns requires a different language from the language of physics and chemistry. For instance, the concept of a spelling mistake is not part of physics.
Likewise opening up someone's head and peering inside, even with the help of tools from the most advanced physics labs, will not enable you to see any sensations, thoughts, desires, plans or emotions. But they exist when the brain is working and they can have real effects. They exist when certain patterns of activity exist in brains: but like the virtual machines in computers we need a special language to describe them. That is why we talk about sensations, thoughts etc., rather than using the language of physics and chemistry. The entities in a mind are not made of matter or energy, but of information and information processes.
More complex virtual machines, instead of doing just one thing at a time, can simultaneously do many things, including interpreting sensory input, generating new goals, deciding between different options, formulating new plans, carrying out previously-made decisions, evaluating what is happening and reflecting on their own mental processes.
A good theory of how human minds work has to describe all this activity and explain how it arises and what its effects are. Likewise anyone designing robots with minds and feelings will have to specify the kinds of abstract processes needed in the robots.
Some interactions between sub-processes in human minds produce emotions like being startled, being amused, fear, excited anticipation, regret, embarrassment, gratitude, jealousy, sympathy and grief. Each of these exists as a result of complex processes and events in virtual machines in humans. When we understand enough about the abstract machines that we call 'human minds' we shall be in a better position to see whether similar processes and interactions can occur in computer-based information-processing machines, in robots, for example.
At this stage in our knowledge there is no reason to believe it possible or impossible apart from wishful thinking. If it is impossible a good way to find out why is to try as hard as we can to make it happen, and understand why it turns out to be impossible. That is also a good way to find out how it is possible, if it is.
Perhaps we shall learn from such efforts that some things are relatively difficult to replicate because they are closely related to physiological mechanisms, e.g. feeling thirsty or itchy, and others relatively easy, e.g. feeling sympathy, embarrassment, grief or pride, because they depend only on non-physical goals, desires, preferences, attachments, beliefs, and interactions between them, requiring little or no replication of animal body states.
Whether we should make such machines is another question. Some such machines may be very useful, for instance intelligent machines helping us in disaster situations where difficult but urgent decisions may have to be made rapidly in novel situations, using ethical judgements and concern for others to drive creative decision making, since previously stored rules and plans do not deal with such situations. Emotions are not necessary in such cases, though motivation and evaluation are.
There are people who fear that machines will turn nasty and try to take over the world. However, I don't think machines can do anything more nasty to us than humans already do to one another all round the world.
For more on this see this talk on wishful thinking in the study
of emotions and intelligence:
Do machines, natural or artificial, really need emotions?
If there's time I may show some simple demos of virtual machines like the ones shown in these movies.
For more information look at the AI Topics web site
and this video debate about 'Machines with Minds' shown on the BBC for the Open University in 2002