Deepinder Goyal’s Temple controversy: What the science says, why doctors are questioning it, and what’s next
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Deepinder Goyal’s ₹85,000 wearable, Temple, has triggered a public disagreement between its founder and medical professionals over whether its sensors can measure blood flow inside the brain and whether its health-related claims are supported by sufficient scientific evidence.
The criticism has been particularly sharp from hepatologist Dr Cyriac Abby Philips, popularly known as The Liver Doc. Goyal has defended the technology, citing research and his personal investment, while promising further validation.
What is Temple and what does it claim to measure?
Temple is a wearable attached to the side of the forehead using adhesive patches. It uses optical sensors to monitor physiological signals and produces two proprietary measurements: BrainFlow, intended to track relative changes in brain circulation, and Entropy, which Goyal describes as a measure of the body’s physiological workload.
The device is linked to Goyal’s Gravity Ageing Hypothesis, which proposes that the long-term effects of gravity on blood circulation could contribute to brain ageing. This remains a hypothesis rather than an established explanation of ageing.
Pre-orders opened on November 1 at ₹85,000, with deliveries expected within approximately three months. Goyal has clarified that Temple is a fitness and wellness device, not a medical diagnostic product.
Why are doctors questioning the claims?
The central disagreement concerns what Temple’s sensors are actually measuring.
The device uses photoplethysmography (PPG), a technique that shines light into tissue to detect changes in blood volume beneath the skin. Its sensors sit near the superficial temporal artery, which supplies blood to the scalp and face. The brain, meanwhile, receives blood primarily through the internal carotid and vertebral arteries.
Dr Philips questioned whether measurements from a superficial artery can establish what is happening inside the brain. In a November 5 post on X, he described Goyal’s response as a “word salad” and alleged that Temple had provided no real proof of its brain-flow measurement claims. He also called the device a “scam”, an allegation that has not been established.
Speaking to a media organisation, Neurologist Dr Sudhir Kumar, said: “The key questions are not whether the signal changes with exercise, stress, or meditation, but whether it reliably measures what it claims to measure, whether it adds information beyond existing metrics, and whether acting on it improves health outcomes.”
In a separate media statement, Dr Praveen Gupta, chairman of Marengo Asia International Institute of Neuro & Spine, told that while gravity influences circulation, “there is no established scientific evidence that its everyday effects progressively damage the brain or cause it to age faster”.
What does the available research show?
Two BrainFlow studies have been published as preprints, meaning they are publicly available research papers that have not completed formal peer review.
The first study, published on medRxiv, compared Temple’s readings with transcranial Doppler, an ultrasound technique that measures blood-flow velocity in a major brain artery. It involved 23 healthy adults, with 20 analysed in each protocol. Researchers reported correlations of approximately 0.8.
However, the paper describes BrainFlow as a relative index, not a direct measurement of absolute blood flow. It also calls for further studies to establish the signal’s cerebral specificity.
The second study, published on bioRxiv, examined 60 sessions involving 44 healthy young men, comparing Temple with a specialised optical technique called time-domain near-infrared spectroscopy. The study was designed, funded and conducted by Temple, with several authors employed by the company. Its authors said further research was needed to rule out residual superficial and systemic influences.
What about Entropy?
Goyal describes Entropy as a score ranging from 1 to 250 that indicates how hard the body is working to sustain itself. Temple has claimed a correlation of 0.93 with metabolic-cart readings across more than 100 exercise sessions.
Goyal's use of the term Entropy draws on a broader area of research that applies thermodynamic principles to human physiology. A 2023 study by researchers from Purdue University, the University of Utah and California Polytechnic State University, published in the International Journal of Design & Nature and Ecodynamics, used data from a NASA human-engineering pilot involving seven participants to develop two entropy-based measures from five physiological signals. The researchers found statistically significant differences in the measures across participants exposed to cognitive stress tasks, suggesting that the approach could help quantify physiological stress responses.
However, they described the findings as preliminary and called for larger studies and further validation. The research did not examine Temple or validate Goyal's proprietary Entropy score.
How has Goyal responded?
In his November 5 statement, Goyal said Temple had cost $30 million to develop, including $20 million of his own money. He cited a 14-day return policy and compared the company’s approach with WHOOP, arguing that wearable companies can launch before publishing validation studies.
On November 6, he revealed plans for a screenless, microphone-free AI companion. He said motion sensors would detect vibrations generated by the wearer’s voice, allowing users to dictate messages, create reminders and record personal information. He also apologised for grouping all Indian doctors together, clarifying that his criticism was directed at a few individuals he described as influencers.
The announcement introduces a new proposition, but does not resolve the original scientific questions.
Temple’s privacy policy also allows certain AI features to use third-party providers to process prompts and device metrics, while Goyal says conversations will remain end-to-end encrypted and never reach model companies.