[SPOILERS] An Alternate Interpretation of Gravity

Since Gravity's release, there have been fan theories that Stone does not live to make it back to Earth, but instead dies at some point during the film and the events we see are a hallucination. There are varying theories on the time and cause of Stone's demise. Some say everything after she drifts off into space and Kowalski never rescues her, others say she is consumed by the fire in the ISS, or that she drowns in the lake. I've even read a theory that the entire film is a dream, and that Stone dies in a car crash when she learns her daughter has died.

The most popular theory is that Stone dies of hypoxia (lack of oxygen) when she turns off the oxygen in aboard the Soyuz. Here is the evidence for this interpretation:

Loss of Consciousness

As the oxygen supply in the Soyuz dwindles, Stone loses consciousness. Everything we see after this point is in Stone's head as her dying brain tries to make sense of her body's physiological state.

The White Light

A common element of Near-Death Experiences is seeing a white light. It is not unreasonable to assume that those who do die experience similar symptoms to a NDE except they, you know, die. In this case, Stone's face is illuminated by the light from Kowalski's helmet.

The Hallucination

A symptom of both hypoxia and NDEs is hallucinations. In NDEs, people often report seeing a holy figure. However, it seems that Stone is an atheist as she says she's never prayed in her life. Stone instead sees Kowalski who represents a father figure, and like most figures in NDEs, he's dressed in white.

The Decision

Another common trait of NDEs is the feeling of reaching a decision point as the person must decide whether to live or die. The question is presented to Stone by Kowalski: "do you want to go home or do you want to stay here?" Stone chooses to live, but unfortunately it's highly-unlikely that a person who has lost consciousness due to a lack of oxygen will regain consciousness without medical intervention. Stone continues dreaming.

Tiangong

Stone's next stop after the Soyuz is the Chinese Space Station called Tiangong, which literally translates into English as "Heavenly Palace".

Euphoria

Stone is noticeably more cheerful after speaking with her hallucination of Kowalski than she was at any point before it. Euphoria is a common symptom of hypoxia.

Hot Flashes

A less common symptom of hypoxia is alternating feelings of hot and cold. Stone mentions that is is getting hot aboard the Shenzhou as it begins to reenter Earth's atmosphere, and during its reentry a fire breaks out.

Seizures

A severe symptom of hypoxia is a seizure. The Shenzhou capsule shakes violently while Stone is in it.

Dizziness and Nausea

More signs of hypoxia represented by the Shenzhou's spinning during reentry.

More White Lights

During her final descent, Stone is once again sees white lights.

Feelings of Suffocation

The smoke from the fire aboard the Shenzhou begins to suffocate Stone, and in her hurry to escape the fire she opens the hatch allowing water to rush into the cockpit. When she escapes the capsule, she is weighed down by her suit and is at risk of drowning. Stone's blood oxygen is depleted.

One Final Thought

Stone resurfaces in a lake surrounded by beautiful, lush green hills. She hears birds and insects as she crawls to the shore, stands up and begins walking. Her final thoughts are of an untouched paradise, and the film cuts to black as her brain dies.