David Sereda, in his book Evidence, The Case for NASA UFOs, explains his discoveries after studying NASA footage of space objects. I will give a short description of his discovery that is easily grasped by the casual reader. For a more scientific explanation, read his book.
Our concept of what an electromagnetic wave is, is limited to a two-dimensional representation. We see the wave as an oscilloscope presents it to us: a linear up and down movement: amplitude (the wave rises up and down) in relation to time (forward propagation). The number of times the wave amplitude cycles up and down per second is expressed in frequency (Hertz).

This model is easy to work with, but it does not reflect reality. A wave does not only move up an down in a forward direction, it actually spins at a 90 degree angles to this forward direction, because it is three-dimensional.

As the wave moves forward at a certain speed, its angular spin velocity must be at least 3.14 times the forward speed, because the spin is a circular movement. For all particles (=wave/mass) that move forward at near or at light speed, it means that the angular spin movement is greater than light speed. But light speed is a barrier in our visible universe. Anything going faster than light speed is just not visible to us. It is there, but we cannot see it. it is, by way of speaking, in another dimension. We see the particles which move in a forward movement at lower or at light speed, but we don't see their angular spin movement, because only light speed and lower than lower speed is visible in this physical universe. It is just a question of terminology of what we call this other dimension. Personally I think that this level of higher than light speed is the etheric, astral, or spiritual level/world, depending on your preference of words.
Now that you understand this, we go the the next step. An electron, which moves around the nucleus of an atom, has very small mass, it moves near light speed. When an electron jumps to a shell closer to the atomic center, it radiates off its energy and reduces its mass. In this orbit it has a higher frequency of its spin. So, when wave-particles move to higher frequency states, they are reducing their mass-energy equivalent (or radiating it outwards away from the core of the mass in the form of electromagnetism). When they move into longer waves, they will oscillate in much lower frequency orbits.
But sometimes the wave-particle relationship of greater mass can be in tighter or smaller diameter waves, but only if the velocity of spin is much slower than for example the near speed of light spin of an electron. The proton (in the nucleus of an atom, is obviously in a much smaller orbit than the electron; but nevertheless it has a very large mass. This can only happen if the velocity of its spin around the center of the atom is much slower.
The new discovery that David Sereda made is, that it is possible to increase the velocity of the spin of an atom (that is the protons, as they make up most of the mass of an atom). When mass comes into contact with higher frequency waves, the mass of an object will raise in frequency (velocity of the spin of the protons increases). This mass will then become lighter and lighter as the mass-gravity effect decreases. Eventually mass becomes as light as photons, actually this is a state of zero mass. "Mass" (or an object) as this high state of frequency has become mass-less in term of the gravity effect, and it will be able to move at light speed. This frequency can be raised even higher towards the infinite, and the speed of the mass-less object will move even faster than light.
Tesla discovered that earth and all physical objects on it vibrate at this spin frequency of their wave-state of about 7-8 Hertz. Einstein saw mass remaining at the same frequency trying to accelerate towards the speed of light, thus ever increasing its mass, requiring a huge amount of energy to continue its acceleration. In this way the speed of light could never be reached, let alone the tremendous energy required to push an object through space whose mass is ever increasing. But changing the frequency of the spin of mass will make it mass-less, and then it requires very little energy to travel at light speed and beyond.`
This is how beings in the universe travel from place to place, from planet to planet, from star to star, from galaxy to galaxy. Well, we call them extraterrestrials, or ET's. The ET's have found the way to reduce the mass-gravity effect of their flying saucers, or shall we just call them spaceships. They convert the mass of their spaceships, and everything and everyone in it, into light by using high frequency wave induction. Once their giant spacecraft are converted into light, they weight in at nothing. The energy required to go light speed would now yield a high frequency wave signal with no mass equivalent to the outside observer. Thus the signal of these spaceships are detected as a high frequency light energy signal with no light, as the whole spacecraft would be made of light. Once a spacecraft is made of light, it can also appear and disappear into the invisible light spectrum (to the human eye and many cameras). A spaceship might be hovering just above you and you will not see it when it is in its high frequency state. Only when they lower their frequency, will the craft become visible. This is what many witnesses report: flying saucers that appear and disappear instantly. Also, spaceships can also appear as just light balls. It is also the answer for the tremendous speeds of observed space crafts, and their instant 90 degree turns without reducing speed, from the observer's viewpoint.

Thus, space ships, or flying saucers, in their high energy state are or invisible to us, or appear as light forms. That applies also to everything inside, living beings included. Some people report that they were visited by human-shaped light forms, or saw them in connection with a flying saucer. Some aliens are able to keep their high energy state when outside their vehicle.

 The following example comes from Bonnie Meyer (in Wisconsin), who was taken by aliens aboard their ship. From her book "Alien Contact" (I left out some details not relevant to our topic):
"Suddenly I realized there was a brilliant bright light in the room; it looked like a very bright spotlight. My eyes were closed, but I still could see what the room looked like during the daylight through my eyelids. It was like going to the beach on a hot sunny summer day and looking at the sun, then closing your eyes seeing the sun shining brightly through closed eyelids.
"I tried to open my eyes; I tried to move but couldn't.....
"All of a sudden I could see three beings in the living room with me. Looking through my closed eyelids I could see what looked like a head with a neck and shoulders. They seemed to be radiating the bright light. ....
"As I calmed down, I realized that I could move and my eyelids would open. The beings looked like what people are now calling light beings. They stood in a golden light so bright that all I could see was an outline of a figure inside this bright light. My yellow fuzzy blanket was no longer on me. I couldn't see it, where did it go? They said, "Follow us." My heart stopped beating fast and I felt love and compassion coming from these beings. I could feel that they meant me no harm. So I got up and stood between them, two in front of me and one behind. We moved single file through the front door, our feet never touching the floor...
"After going through the front door of the living room, my mind demanded clarification. Wait just one minute, how could we go through the door without opening it? I could feel them smiling at my questioning mind. We crossed the street in front of my house. There was an open field and in the middle of it was a small ship on the ground. It was round, saucer shaped, about 30 feet in diameter, silver in color, and standing on three legs. On the other side of this open field is Highway 41, which is one of the main north and south highways in Wisconsin. I was thinking, it is late, there are only a few cars on the highway, but no one seemed to see this unusual sight. None were stopping to look at us or the craft. Why weren't the cars stopping? How could they not see what was going on? The being answered in my head: "We have a force field up, so they cannot see the ship. We can do this anytime we wish; that is why we are only seen when we want people to see the ships."
"I don't remember how I got into the small craft, just all of a sudden I was inside. It looked larger from the inside that it looked on the outside. The three beings who escorted me to the craft were the only ones on board. But wait a minute, now that we were inside the craft they did not look like light beings anymore. Could this be because of the difference in the earth's atmosphere or vibrations to what was inside the ship? I didn't know, but it seemed reasonable to me. They looked almost humans now that it was easier to see them...."

The story goes on but the rest is not relevant to our topic here.
Here Bonnie Meyer sees the alien beings originally as light forms. But once inside the ship her own body has been raised in frequency. Being of the same wave frequency of the ship and of the beings, she then sees them as "normal". Everything in a high frequency state looks just as "normal" as in a low energy state. It is only to an outside observer that the ship and beings look like light forms.
Another characteristic of matter being in the high frequency state is that its mass and gravity are reduced. The higher the frequency of the wave state of an object or being, the less its mass and its gravity becomes. At a certain point it can move freely through physical objects. Bonnie Meyer noticed that they were moving through a closed door, and she wondered how this was possible. It was possible because she was already higher in frequency than her normal physical state. She also noted that their feet were not touching the floor. Again a sign the gravity effect had nullified due to the raised frequency. Those two characteristics, beings moving through walls, and floating along above the ground is widely reported among people who are/were visited or abducted by aliens.
In our physical universe nothing can go beyond the speed of light as long as the frequency of the wave state of matter remains the same. Science has made this very clear. A material object will never attain the speed the light. Light is the barrier in this physical universe. Anything that vibrate at a higher wave state than light is invisible to us. That level of existence beyond the state of light is given different names in different traditions: the spiritual world, the etheric or ethereal world, the astral and mental world. All these worlds interpenetrate and are right in the here and now. The spiritual worlds are as real as the physical world. They are up there in the clouds somewhere. They are here and now, with the only difference that they are in a higher frequency state. Change your frequency state and you disappear from the physical world, and shift into the astral world. Human beings can go there another way. Besides a physical body we also have an astral and mental body. When we shift our consciousness from the physical body to the astral body, then we can experience this higher frequency state/world. It happens during sleep, during meditations, during out-of-the -body experiences. It is possible because we have already the means, another body, that has this higher frequency state.

Steven Greer, director of the Disclosure Project, (more about him in the next chapter) also noticed the similarity of the high frequency state of wave forms and what we call the astral level. He says that some of the advanced technologies and capabilities of extraterrestrial civilizations, especially those interfacing with mind and thought, can appear in ways very similar to so-called 'astral' or spirit beings. Nevertheless they are in a higher state of physicality, manipulated by advanced technology.

 "When something is dematerialized for even a brief period, the resonance frequency of that object has shifted into an etheric quasi-plasma form of energy that closely approximates astral energy. Now, there are different gradations within the astral realm, from a coarser astral that is interfacing with the material existence of atoms and electromagnetic energy, all the way to the finest astral, which is called "high celestial". Every level of the astral can be interfaced technologically, if your sciences are refined enough."
"From what I have observed, this is done through very high energy physics and electronics which literally phase shift, in one quantum leap, the material ET craft and all its occupants into an aspect of the cosmology which closely approximates what we know as the astral world. This is done through a complex interaction between powerful rotating electromagnetic fields and the gravitational field and mass inertia. When the craft is on this side of the crossing point of light, it is seen like any other material, manufactured object, but it can maneuver in ways which appear to negate mass inertia and gravity. Once it phase shifts onto the other side of the crossing point of light/matter, it seems to disappear. But it has not. While in that form or energy spectrum (or dimension) the craft can hover, or move within the material universe at many, many multiples of the speed of light. The velocity is non-relativistic, at least as measured on this side of the light barrier. However, 1000 light years will not be traversed instantly because there is an element of 'drag' as it moves in this aspect through the material cosmos. Put another way, there is a component of the object which adheres to the underbelly of the material cosmos and there is a coefficient of cosmic drag which prevents the transport from being instantaneous across vast interstellar distances. Operating, then, in a sort of 'junction' between aspects (or dimensions) the ET craft can phase between either. Actually, it can also be partially in both. The spacecraft then can be hovering outside the SETI Institute - and remain undetected by them unless it pops into the material aspect fully and then only if the people in the building bother to look outside, see the device- and honestly report it."