The science of finding a virus that causes a disease.

If it is believed that a virus causes a new disease, then samples are taken (blood, sputum, secretions) from a few hundred people with similar symptoms.
Without mixing the sample with other tissue or products that also contain genetic material, the virologist macerates, filters and ultracentrifuges the sample, to purify it to find only the virus.
This then allows the virologist to show (using electron microscopy) thousands of identically sized and shaped particles.
These particles are the isolated and purified virus which are then checked for uniformity, and then may be further characterized.
If we have come this far then we have fully isolated, characterized, and genetically sequenced an exogenous (from outside the body) virus particle.
However, we still have to show that the virus is the cause of the disease. This is done by exposing a group of healthy subjects (usually animals) to this isolated and purified virus in the way in which the disease is thought to be transmitted.
If the animals get sick with the same disease, as confirmed by clinical and autopsy findings, one has now shown that the virus actually causes the disease. This demonstrates infectivity and transmission of an infectious agent.

None of these steps has even been attempted with the SARS-CoV-2 virus, nor have all these steps been successfully performed for any so-called pathogenic virus.
Quote taken from a statement of virus isolation by:
Dr. Andrew Kaufman, MD.
Dr. Thomas Cowan, MD.
Sally Fallon Morell, MA.
and supported by over 10,000 voices around the world.

What has happened instead.

Instead, since 1954, virologists have taken unpurified samples from a relatively few people, often less than ten, with a similar disease.
They then minimally process this sample, and inoculate (put) this unpurified sample onto tissue culture containing usually four to six other types of material — all of which contain identical genetic material as to what is called a “virus.”
The tissue culture is starved and poisoned and it naturally disintegrates into many types of particles, some of which contain genetic material.

Against all common sense, logic, use of the English language and scientific integrity, this process is called “virus isolation.” This brew containing fragments of genetic material from many sources is then subjected to genetic analysis, which then creates in a computer-simulation process the alleged sequence of the alleged virus, a so called in silico genome. At no time is an actual virus confirmed by electron microscopy. At no time is a genome extracted and sequenced from an actual virus.
Quote taken from a statement of virus isolation by:
Dr. Andrew Kaufman, MD.
Dr. Thomas Cowan, MD.
Sally Fallon Morell, MA.
and supported by over 10,000 voices around the world.

I've created a course you can take for free here that has the full text of the statement of virus isolation.