Science succeeds by failure, just as surely as it works by success. We slowly come to know how the physical world works by learning that what we thought was true is all wrong.

Science teaches us to look more closely, to see more clearly. We decide that a theory is valid only when it is proved by experimentation and that experimentation can be replicated, and if it cannot be, we learn from this too and say: Here are the limits of what is possible now. Science is valid because it cannot be taken on faith alone.

But now the world has seen the tragic unraveling of a remarkable series of scientific successes made in stem cell research, a technology that had excited scientists and that promises much for doctors seeking ways to heal by making new tissues that could replace organs, nerve cells, bone and muscle lost to injury or disease.

How could we have seen it coming? All the mechanisms of scientific integrity and a skeptical media were engaged in reporting the apparent successes. In the last two years, South Korean researchers at Seoul National University seemed to have been remarkable in their skill, dedication and ethical processes. They had apparently not only been the first to clone human embryos and derive a line of stem cells from them, they had been the first to clone a dog, known to the world as Snuppy.

In the research now under fire, they had claimed to be able to create stem cell lines that were perfect DNA matches for particular patients and to do so with remarkable efficiency, at the rate of one line of cells from each donor cycle of eggs. This marked a critical step in the production of transplantable human tissue. But preliminary reports released by an investigative panel at Seoul National University say that nine of the 11 stem cell lines were apparently fabricated.

We believed in the research, in part, because we liked the idea of the hard-working scientist from a humble background in a small, energetic country who leads the way with his intellectual skills and his dedicated team, working around the clock for human good. We liked that the South Korean researchers engaged in "brotherly" collaboration that included American scientists, and that leadership roles were given to women.

The South Korean research seemed above reproach in ethics as well: The scientists had a long public debate about the moral issues, voted for strict standards for ethics review and brought in a team of philosophers, theologians, lawyers and ethicists to craft a policy of anonymous donation for egg donors eager to volunteer without thought of payment. Bioethics scholars, myself included, stood at their side as Science, the most respected peer-reviewed journal in the field, announced their new achievement.

But then two of the project's key scientists announced in the international media that they were abandoning the team, and a third called for an investigation into all the work, leaving Dr. Hwang Woo Suk, who had been named as South Korea's "supreme scientist," to defend and explain.

Escalating sets of charges and countercharges — first mismanagement, then deceptions, then cover-ups of deceptions — emerged. The voluntary, consent-based egg-donation process was tainted by a disclosure that the team's second author, in charge of the in vitro fertilization clinic, had paid for eggs. And two junior team members had felt it so important to get eggs for the project that they secretly donated their own and then, when found out, successfully pleaded not to be named. When the media revealed the secrets, the pair first hotly denied it and then admitted it and apologized.

Then the science itself was attacked — by the same people who had once called one another brothers and seemed to genuinely mean it. One by one, scientists called competing news conferences to claim terrible things — lying, sabotage of data. We were told of faked pictures, cover stories and switched data. And now comes the disturbing confirmation from the university panel in Seoul.

For many, it has disheartening familiarity — dueling experts with pictures and charts you could not verify and could not really know whether to trust — but this time, it is not CEOs or politicians, it is scientists we had come to trust and deeply respect.

How could that have occurred? Serious new questions will be raised about the ethics and integrity of such research. We will have to wait for the investigations to be concluded before we can understand the complexities of the whole story.

The bottom line is this: In a complicated world, the public must trust experts, because how can you know what to do if you cannot know what is real? "Tell the truth, always," we teach students, "withhold nothing from your data." It is a categorical imperative for science and indeed for all societies.

Stem cell science is particularly complicated because it has become a part of the political discourse, too — the research touched on old debates about embryos, women and the American fascination with moral status, rights and duties. Cloning talk is talk about death as surely as it is about birth. Stem cells are not just about stem cells but are part of a debate about life, death and religion and our terrible fears and hopes for the future.

The politicization of the discussion only makes the truth more important. In science, we struggle to discern what is good — first technically good, and then morally good, and we struggle to sort out wild claims of cures and wild threats of harms from the slow and iterative process of real science.

In the edgy new science that tests our political compacts, that asks much from a pluralistic American democracy, that has the possibility to change the very nature of human capacity and of human dreams, the truth needs to be told with utter urgency.

In every bioethics case we have seen in this contentious year, in which issues at the end and the beginning of life suddenly were fought in the fiercest of ways in the public square, honest data matter a great deal — it is where we must begin. It is the deal we make with any expert.

The core idea — that at the earliest stages of development, all beings begin with a set of identical cells that could turn into any cell — is a powerful one that will be studied, understood and, with courage and tenacity, luck and grace, used to treat suffering and waiting patients. That is not a fantasy, and that is not a fraud.

Laurie Zoloth is a professor of medical humanities and bioethics at Northwestern University. She wrote this commentary for the Los Angeles Times.