Diverse Quantum Field Theories and inter-related issues are presented here, accompanied by associated questions, philosophical discussions, and insights. This article includes among others, a discussion about the beginning of our universe, time-space observations, and the non-deterministic needs for actual experiments to prove theories in physics, specifically the possibility to ascertain the existence of an object in space without necessarily interacting with it. Part of the issues discussed here is more philosophical rather than in the realm of theoretical physics.
Special relativity was introduced in 1905. It tells us how motion, time, and velocity are relative to the observer and they are not absolute. Also, we know that particles cannot exceed the speed of light. General relativity, which was introduced in 1915, is about gravity and tells us how space-time is bent due to mass while affecting particle motion.
Quantum Physics explains the interaction between particles, which constitute the matter and their related forces, namely, it explains how everything works. Einstein was among the first physicists who described the evolution of ideas from early concepts to relativity and quanta  and the introduction of gravitational waves .
There are several quantum theories. Quantum Mechanics was developed in 1920 by Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and others. It tells us, among others, how the position or momentum of a single or more particle changes over time.
There are three forces that matter interacts with: electromagnetism, which explains how atoms hold together, the strong nuclear force, which explains the stability of the nucleus of the atom, and the weak nuclear force, which explains the radioactive decay of some atoms. These three theories were assembled under the umbrella called the Standard Model of particle physics. The problem with this model was that it did not explain why matter has mass.
The existence of a particle that gives all other fundamental particles their mass, was predicted by Quantum Field Theories (QFT) over five decades ago and proved recently (2012) by Higgs .
Almost everybody agrees that the universe had a definite starting point. Some physicists believe that the actual point or time of creation cannot be explained by the currently known laws of physics. We are aware of the existence of gravitational waves that are caused by the movements of large masses. Those waves were predicted by Einstein and they are included in his theory of general relativity.
13.8 billion years ago, the Big Bang occurred . Accordingly, this is the distance that the observable universe may extend, which is 13.8 billion light-years. We may assume further that the space-time beyond that distance might be another universe and so there might be multi-universes or multiverse. We may argue about the Big Bang that generated our universe. What if there was more than one Big Bang? This assumption may lead to the existence of a multiverse.
A new era for the understanding of our universe may be started recently by the discovery of Higgs boson. A boson is a type of subatomic particle that imparts a force. Peter Higgs tried to explain why certain particles have mass and others do not have mass and they float in the universe like photons of light. According to Einstein, E=mc^2 means that energy and mass are equivalent to one another, that is mass m=E/c^2 accordingly, if we add enough energy we may create mass. We have had endless debates about how the universe began and what was before that. My assumption based on many arguments is that the only way we do not violate any conservations laws is to assume that our universe was created out of nothing. There might be another theory that supports the idea that there's no end or beginning to the creation of our universe.
Time, Space, and Relativity
We use the word time directly and indirectly very often in our daily conversation and throughout our lifetime: time is money, time of life, time after time, between times, gain/loss of time, good/bad time, slow/fast time, right/wrong time, before/after time, present time, past time, real-time, on time, in no time, kill time, any time, every time, plenty of time, timeless, time limit, time cycle, time cures, and time flies...
Time is depicted by artists in various ways, among them the famous 'melting clocks' by Dali. We can distinguish between pure time, relative time, and absolute time. Time measurement is the unit of time to which all time measuring devices ultimately refer to. It is a point at or a period in which things happen, a repeated instance of anything or a reference to repetition, the state of things at any period.
Space is that part of the boundless four-dimensional continuum in which matter is physically rather than temporally extended. Relativity recognizes the impossibility of determining absolute motion and leads to the concept of a four-dimensional space-time continuum.
The special theory of relativity, which is limited to the description of events as they appear to observers in a state of uniform motion relative to one another are developed from two axioms: The law of natural phenomena is the same for all observers and the velocity of light is the same for all observers irrespective of their velocity. Space and time in the modern view are welded together in a four-dimensional space-time continuum.
There is no clear distinction between three-dimensional space and independent time. Time means different things to different 'observers'. This may not agree with the axioms (on which the special relativity theory is based) described earlier, at least not from a psycho-philosophical point of view.
These 'observers' may include people (humans), animals, plants, clocks, and other beings outside our time universe. Time seems to be different for different people: age, education, origin, mental stage, and religion may all affect. Time appears 'slow' when we are young and 'fast' as we grow older. Time seems to be passing faster when we are enjoying ourselves or when we are busy, as opposed to when we are bored or idle. The description of time-related events in the history of humankind differs in different cultures.
Clocks and other similar instruments measure time and tend to be almost identical in terms of information about it. This is to be expected as we designed them all to measure time defined to be consistent within our universe. Time is continuous concerning our universe and within it, and it is relative to our observations. When we observe a moving object between two points we 'see' it traveling all the distance between the two points, so we assume that this continuity of observation means that time is continuous. This may not be the case, however, if we perform our observation in another galaxy or in another dimension, where these rules are not necessarily valid. In the digital domain, as opposed to the analogue domain, we may observe the same continuity of moving objects. The time is digitized, however, and between two consecutive time points there is a gap of a certain fraction of a time unit, equivalent to the sampling resolution, where 'anything might happen'.
For other creatures, these time gaps may represent their entire lifecycle, or we may be living within our time with another life form, whose time resolution fits with our 'dead times', which are our time gaps. Television is viewed as continuous moving pictures, whereas actually, it comprises discrete individual pictures, projected at thirty frames (or more) or pictures per second. Time can be measured, viewed, and evaluated. The observer's tools for the evaluation of time are his/her senses. Unfortunately, senses can be fooled.
Strobe light projected onto a rotating disk will generate the illusion of a still disk. Are our other observations wrong or at least inaccurate, then, particularly if we are a small subpart or subspace of a much larger and more complex galaxy?
In the laboratory, we have successfully accelerated and slowed down certain processes, such as chemical or other natural processes. These experiments offered the possibility to control processes that were functions of time. Certain processes were successfully reversed to what they were before, indicating 'pseudo going back in time', which is not going back in time, but it looks like it.
The introduction of computers generated a revolution in time-related processes and enabled not only the observation of past and present time-related phenomena but also predictive processes, which are future time-dependent scenarios. Time affects our entire lifecycle, our birth, our life, and our death. Our heartbeats almost once every second and our inner biological clock operate throughout our life. If we overturn this clock by flying to another time zone, our body suffers a phenomenon known as jet lag and it takes some time to adapt to its new condition. Time affects most of the processes and phenomena on earth, some faster and some slower. If there are time-independent phenomena or a phenomenon that until today has seemed to be unaffected by time, then these scenarios must be classified as 'past, present, and probable future' .
As the observer's time is limited, we are unable to analyze these timeless phenomena without using certain assumptions and predictions.
According to Einstein, time is more like a river, flowing around stars and galaxies, speeding up and slowing down as it passes massive bodies. One 'second' on the earth is not one second on Mars. All materials, including all known life forms and other mass-owned celestial bodies, are time-dependent. In time we have the interval between past and future, while in space we may remain in the same place. Time has a sequential moment that follows one another, so it seems time is moving and moving in one direction .
Since the 1920s we know that energy isn't continuous and we are not made of particles but we are made of fields. The field is not allowed to stay still, according to the Heisenberg Uncertainty
uncertainty principle (1927), accordingly, we cannot simultaneously measure the position and the velocity of an object.
Physicists and philosophers may have overlapping and common views of theories. Both may believe in theories that they can't prove. Some theoretical physicists may believe in their theories even when they don't have empirical or experimental proof.
String theory links quantum mechanics with Einstein's theory of relativity. In general, the theory states that subatomic particles are very small one-dimensional strings, not zero-dimensional points and they are constantly moving or vibrating. However, currently, we can't test the validity of String theory, yet most physicists believe it's viable. Einstein never conducted a single experiment; all his theories were predictions, assumptions that years later some of them were proved by an actual experiment.