Zhejiang University denies developing invisibility cloak: Theoretically feasible but current technology cannot achieve it

Recently, a video circulated online claimed that a Chinese university had developed an "invisible cloak", and some netizens said that the university was Zhejiang University.

A video circulating online shows an old man unfolding a piece of "plastic sheet" and his lower body "disappears".

After the old man put away his "invisibility cloak", his body "reappeared". Yesterday, experts from Zhejiang University believed that the video was a post-production synthesis.

This edition's pictures/WeChat "tiexue360" video screenshots

An old man holds a piece of plastic sheet, facing the camera, unfolds it, and raises it above his head. In the picture, the old man "disappears", and only the flowers, plants and trees in the background remain.

In recent days, a video titled "Grandpa disappears in an instant" has attracted attention online. Many self-media WeChat accounts forwarded the news, saying that Zhejiang University has successfully developed a domestic "quantum invisibility cloak" that can "make people invisible" like magic.

Yesterday, a Beijing News reporter confirmed from Zhejiang University that although the research on stealth technology was launched many years ago, the so-called "research results" circulated on the Internet have nothing to do with Zhejiang University. Stealth technology expert, Professor Ma Yungui of the School of Optoelectronic Science and Engineering of Zhejiang University said that stealth technology is currently completely feasible in theory, but there are still many difficulties in practice, especially for civilian use, there is still a long way to go.

Domestic "quantum invisibility cloak" rumored on the Internet has aroused doubts

In front of the camera, an old man in ordinary clothes with a big smile on his face, holding a piece of "plastic sheet" in his right hand, walked down the stairs among the flowers, plants and trees. Then, the old man shook out the "plastic sheet" and slowly raised it above his head. As the "plastic sheet" rose, the old man gradually "disappeared", leaving only his hand holding the edge of the "plastic sheet", still "suspended" in the air.

Such a video has recently attracted widespread attention, and "the old man disappeared in an instant" has quickly become a hot word on the Internet. The Beijing News reporter noticed that many Weibo and WeChat public accounts claimed that the old man was not holding a "plastic sheet" but a domestic "quantum invisibility cloak" that can achieve the invisibility function of the human body and is a "major technological breakthrough" developed by Zhejiang University.

However, doubts also came along. Some people said that the video circulated on the Internet may be spliced ​​together, not "invisible", and the fact that "some leaves are shaking and some are not moving" at the same time in the video is proof of this. An industry insider engaged in video production told the Beijing News reporter that judging from the picture effect, this video should have been edited using the matte technology. The specific shooting process is to first shoot an empty shot with no one in the room, and then have the old man hold a blue or green cloth and shoot it again, then combine the two videos and remove the blue or green cloth. "The bright spots in the video are the positioning points for the matte, and this technology is very common in film and television post-production."

The Beijing News reporter found that as early as three years ago, a foreign netizen had uploaded a similar video. However, the video finally revealed that the so-called "invisible cloak" was actually a piece of green cloth, which was produced through post-production synthesis.

Existing technology is not enough to develop an "invisible cloak"

Yesterday, a staff member of Zhejiang University told the Beijing News that after the news of the domestically produced "quantum invisibility cloak" appeared on the Internet, they had sought confirmation from experts in the field of stealth technology within the school, and the response they received was "I don't know what's going on" and "there is no literature or discussion on this issue in the academic community."

Ma Yungui, an expert on "invisibility" technology and a professor at the School of Optoelectronic Science and Engineering of Zhejiang University, confirmed to the Beijing News that Zhejiang University has not developed a domestic "quantum invisibility cloak" nor has it filmed a video for release. Even the "quantum invisibility cloak" itself is a pseudo-concept. He said that under the current technical conditions, it is not possible to produce the "invisibility cloak" in the video circulated online. After watching the video, Ma Yungui also said that he was more inclined to the statement of "post-synthesis".

The above-mentioned Zhejiang University staff member said that the reason why the video circulated on the Internet was labeled "Zhejiang University Product" is related to the fact that Zhejiang University has been conducting research on stealth technology.

The Beijing News reporter noted that in October 2013, the research team of Chen Hongsheng from Zhejiang University published a paper titled "Achieving the Invisibility of Large Objects in the Visible Light Band - The Mechanism of Electromagnetic Wave "Invisibility Cloak"" in the authoritative scientific journal Nature Communications. However, the media reported at the time that the principle of this "invisibility" technology is to absorb electromagnetic waves and minimize the reflected electromagnetic waves. The project team once said that it is still very difficult to make an invisible cloak that can be worn on the body due to technical bottlenecks such as demanding material parameters and insufficient lightness.

■Dialogue

Ma Yungui, Professor of College of Optoelectronic Science and Engineering, Zhejiang University

"Invisibility cloak" is theoretically feasible, but there are still technical difficulties

Ma Yungui is a professor at the School of Optoelectronic Science and Engineering of Zhejiang University. He has been researching new opto-electromagnetic modulation technology, artificial opto-electromagnetic materials and devices for a long time. He is also one of the earliest researchers in China to focus on "invisibility" technology. Ma Yungui told the Beijing News that "invisibility cloak" is theoretically feasible, but it is still difficult to implement in practice, especially to achieve civilian use, which still has a long way to go.

"Technically, it is not possible to make an 'invisible cloak' for the time being."

Beijing News: Does the concept of "quantum invisibility cloak" really exist?

Ma Yungui: There is no concept of "quantum invisibility cloak" in the academic community, but there is the concept of "invisibility cloak", which is a multidisciplinary research topic involving optics, electromagnetism, mathematics and other disciplines.

Beijing News: So how true is the “invisibility cloak” rumored on the internet?

Ma Yungui: This cannot be true. There is no way to achieve such an effect technically. I have read some opinions and I am more inclined to believe that the video was produced using matte technology.

Beijing News: How to define "invisible"?

Ma Yungui: Normally, people can see objects because the surface of objects scatters light. If light can bypass people, turn from the front to the back, and then completely restore the incident light state, the "invisibility" effect can be achieved. For example, if water drops directly above a glass ball, the water droplets disperse and slide across the surface, turning around the sphere, and then converge in the lower half and continue to fall straight down. If light can achieve a similar perfect turning process, "invisibility" can be achieved.

Beijing News: Are the definitions of “invisibility” consistent in scientific research and daily life?

Ma Yungui: Strictly speaking, the definition of "invisibility" or "invisibility cloak" in scientific research and daily life is the same, both of which are to achieve "invisibility" by allowing light to perfectly bypass objects and continue to transmit in a straight line. However, in the field of scientific research, the concept of invisibility is broader. For example, there is also the concept of "invisibility", which means that the reflected echo cannot be detected, etc., and it does not mean that "the light must be perfectly turned."

Beijing News: Why do we need to study “invisibility cloak” technology?

Ma Yungui: Scientific research generally has two driving forces, one is driven by scientific value, and the other is driven by practical application. Invisibility cloak technology is currently mainly driven by science. This technology has great scientific significance and is expected to have disruptive applications in the future. In this area, research at home and abroad is almost carried out at the same time, and the challenges faced are also common.

“There is still a long way to go before it can be used in civilian applications.”

Beijing News: What progress has been made in the research on “invisibility cloak”?

Ma Yungui: Recently we have made a new progress, which can make metal "invisible", for example, making it impossible for electromagnetic induction detectors to effectively detect it when passing through security checks.

Regarding the "invisibility cloak", it is completely feasible in theory, and the relevant mathematical models and solutions already exist. The key is whether it can be done and whether there is a way to turn theory into a solution. This is still quite challenging.

Beijing News: Where do the difficulties in research mainly lie?

Ma Yungui: At present, we can verify the feasibility of the technology through local experiments. For example, we can achieve invisibility at a certain frequency, or within a certain angle range. However, it is not technically possible to achieve an all-round invisibility cloak like an "invisible cloak".

The main reason is that light is a very complex physical quantity, and it is very challenging to meet its stealth requirements. What we call "invisibility cloak" in daily life actually refers to invisibility in visible light, but according to the length of the wavelength band, light can be divided into infrared light, microwave, etc., all of which need to be studied.

Beijing News: What are the future application scenarios of “invisibility cloak”?

Ma Yungui: It is mainly concentrated in the field of national defense. The principle of the current "stealth aircraft" is that the fuselage absorbs all electromagnetic waves or reflects them to other places, making it impossible for radar to detect them. If similar "invisibility cloak" technology can be realized, allowing electromagnetic waves to bypass the aircraft directly, then a more ideal stealth effect can be achieved.

Beijing News: So there is still a long way to go before “invisibility cloak” becomes part of our daily lives?

Ma Yungui: Yes, there is still a long way to go before the “invisibility cloak” can be used for civilian purposes. The current application of invisibility technology is still in the military. In terms of civilian use, it is still in the conceptual stage of scientific research and has not yet reached direct application.

As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity.