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The following material is from the Energy Science & Technology Conference 2018 website, linked above. In his interview which I just heard, David explains that his relentlessly frustrating attempts at presenting this material was finally opened up at this Conference, when he had expected the same old rejection and coldness he had received from others in the past, as though the word "antigravity" was a by-word that turned OFF the attention of everyone he had spoken to. At this Conference, suddenly there were interested men from all over the world lining up to speak with him and he ended up talking to them in turn for a straight 12 hours from 8 am to 8 pm. David mentioned that high-speed space travel is a by-product of this technology, and he has been told that speeds exceeding that of light is quite possible, by using it.
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At one point years ago, at another event of this kind, a mysterious man with his name tag REVERSED had told David that there had been a team of 14 government mathematicians who had gone over his father's formulas and had found them correct, and so forth. David asked him what his name was but the man excused himself and walked away, and David never found out who he was or whom he had represented. He did not want to tell his father about this man for fear he would be upset about it, but about 2 months before he died, David told him, having concluded that he must divulge the truth before it was too late, and his father was very upset, as David had thought he would be. Effectively, this governmental entity had chosen to engage in reverse-engineering certain artifacts held in top secret seclusion such that they were able to discover what made them work, but they had deliberately excluded Frederick from being involved in their research, ostensibly because the security clearance he would have needed was beyond his grasp. This was very disappointing to the inventor, and he died later carrying this grief with him to his grave:
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Thanks for posting this information. My husband and I listened to David last night. Very feasible.

Interesting.  Tesla also figured this out, but his work was suppressed by the government.

Sounds to me like he too has concluded that gravity is actually related to electromagnetism (from the mention of using an EMF to control it).

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A caller asked David about Tesla and if David's father was using the same theory as Tesla. He replied that while the two men were dealing with the same sub-atomic reality, therefore their work was very closely related, they were approaching it from two different directions. But the concept of free energy for everyone is at the end point of both approaches. Tesla might have been getting really close to anti-gravity but his major objective was how to transport electricity over distance without the use of physical conductors or wires. The powers that be had to control that because they want to keep everyone paying an electric bill, habitually, every month. Forever.
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The "men in black" descended on the personal effects of Tesla when he died, and carried it all off, perhaps because he had no family to protect it. Frederick Alzofan had family, including his son David, so perhaps the goons would have had an obstacle there that could have turned into a national scandal if they had tried to violate the family's privacy and property. Another Waco TX kind of thing.
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But David describes some things that are very similar. He said when he was a young boy his father told the family that their phone was being tapped, so this was a normal state of affairs for them. And Frederick said he wasn't able to get a high enough security clearance to be able to access the secret warehouses he needed to get into in order to fully develop his experiments. He did have a security clearance but it wasn't high enough for that.
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He says the various UFO sightings that are being reported lately but no longer being denied by "official spokesmen" like they used to do (saying they were weather balloons or northern lights or whatever) are indicators that the cat is now out of the bag, and an unstoppable portion of the American population are aware that black opps projects include anti-gravity aircraft, because regular planes just don't move like these things are seen moving, even by the credible testimony of experienced pilots and senior military personnel.
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How many years went by with government spokesmen denying the existence of the stealth fighter, but when the Gulf Non-War broke out (sort of) the F-117A was right there on the TV news so they couldn't deny it anymore. I was in the north San Fernando Valley in 1997 when they had the big Van Nuys Air Show going on and I looked up from my front yard to see the B2 Stealth Bomber hanging in the sky like a Christmas tree ornament. It was moving and turning, even up and down, doing u-turns right over the treetops, but so very slowly, and making no sound whatsoever. I had to pinch myself. And no, I was not dreaming. So I know it's real. That was 21 years ago. 
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The P-51 Mustang was developed, won the War in Europe, and became obsolete all in 3 years. What changes and developments do you suppose might be possible in 7 times 3 years?
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The host of the show mentioned after a caller told his story, that he finds this theme is very common among UFO sightings, that when a group of men all see the same thing in the sky, a strange craft that moves and has lights like nothing they've ever seen before, after it's over, they all look at each other without talking, with a look that says, "Did that really happen?" They don't have anything to say even to each other, and they go their separate ways perhaps for years without telling anyone what they had witnessed. And no one has been able to answer the question, "What makes them so reticent?" Nobody seems to know what this mysterious wall of silence is, that imposes itself on people who see these things. Some people do speak up, but they say that everyone in town shuns them, and the way small town America behaves can be quite influential on your self-perception. Eventually you start to think there must be something wrong with you. Or maybe you just imagined the whole thing.
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Like you've woken up to find you're living in an episode of the Twilight Zone..........