What I love about buddhism is, all the claims are supposed to be verifiable with personal empirical experience. "Ehipassika".

I understand some are able to perceive past lives, with various techniques.

How can one know if this is simply a trick of the mind, or a reality?

If scientists were to design an experiment to discover if this is true or false, how would you go about it?

Not a buddhist but if you practice with some kind of imaginal practice (I'm currently doing dream yoga) then you can view entering a dream as a rebirth.
The onotological status of these experiences are hard to determine, but you can still derive value from them by practicing
morality and using it as a simulator to learn from experience it would still have an effect upon you. Empirically effects like jhana are also amplified
during dream state, so mental moves seem more observable like learning to move between the jhanas.

Experiences that feel "real", with that noetic quality of "truth" that would seem to strongly imply rebirth can definitely arise in some practitioner and even occasionally non-practitioners, particularly young children.

As noted above, issues of ontology are complicated, though there are fascinating documented case series at places like DOPS at UVA with curious evidence.

As noted above, they can also sometimes provide deep psychological insights that can be valuable (or sometimes not so valuable) regardless of issues of ontological verification.

Even within Buddhism, one finds it explained both ways, meaning that rebirth is real or not real, depending on the frame of reference. Through a first or second training point of view, the "form" or "compassion" end of things, there is rebirth and karma, a past, a future, and all of that. From a third training point of view, the "emptiness" end of things, there is no rebirth, nothing to be reborn, nothing separare, only transient sensations arising and vanishing now, no past, no future, and this moment to insubstantial to withstand scrutiny.

Both frames can be helpful from a pragmatic point of view, depending on the practitioner, practice, phase of practice, goals, etc.

I know Sadhguru has talked about how he had past life experiences, and has recognized people from his current life in them, and then helped said people recall their own past lives and confirm that they were friends in past lives. I suppose, if that's true, that would confirm it. I haven't had any past life experiences myself so I can't speak for any validity, but if that's possible I suppose that's one way of validating.

I want to be respectful and reply to all these awesome comments, but they really leave me lost for words.

Will try to reply if I can achieve brainfunction later.

Dr. Ian Stevenson was a scientist who studied reincarnation.

https://med.virginia.edu/perceptual-studies/who-we-are/history-of-dops/dr-ian-stevenson/

He studied children with verified memories of past lives, some of whom had an rare type of birthmark at a location on their body that corresponded to an injury in the past life.

They don't.  I was raised catholic. How do we know heaven in real. Faith they say. Hmmm . Even buddhism which  seems more rational and less dogmatic  contains an element of faith.    I don't think NDE are hard evidence  of an Intermittent  state ,Christain or Buddhist. However  it should be studied  I believe.

I asked ChatGPT the following question:

If scientists were to design an experiment to discover if rebirth were true or false, how would you go about it?
Here is the reply:

The concept of rebirth, which is also known as reincarnation, is a philosophical and religious idea that is not currently supported by scientific evidence. However, if scientists were to design an experiment to investigate the possibility of rebirth, they would need to develop a rigorous experimental protocol that could be replicated and tested by other researchers.Here are some general considerations for designing an experiment to investigate the possibility of rebirth:

1. Define the hypothesis: The first step in designing any experiment is to clearly define the hypothesis that you want to test. In this case, the hypothesis would be that rebirth is a real phenomenon that can be scientifically verified.
2. Develop a study design: To investigate the hypothesis of rebirth, scientists would need to design a study that could collect and analyze data in a systematic way. This might involve identifying individuals who claim to have memories of past lives and comparing their statements to historical or archaeological records to determine their accuracy.
3. Select participants: Scientists would need to carefully select participants who claim to have memories of past lives and verify their claims through interviews and other forms of data collection.
4. Collect and analyze data: Scientists would need to collect data from the participants and analyze it using statistical methods to determine if there is any correlation between their memories and historical or archaeological records.
5. Replicate the study: To ensure the validity of the results, the experiment would need to be replicated by other researchers using the same or similar methods.

It's important to note that the concept of rebirth is not currently supported by scientific evidence, and designing an experiment to investigate it would be a significant challenge. Additionally, any study that seeks to investigate the possibility of rebirth would need to be conducted with sensitivity and respect for the beliefs and cultural traditions of the individuals involved.

It may help to examine the other options . The usual one is that subjective experience is a byproduct of brain chemicals. If you actually scrutinize that idea, it's pretty trippy.  To me it's actually more magical & fantastical than the rebirth option, which simply posits the serial continuity of moments of experience in a continuum, similar to other continuums we observe in daily life & science.

Indeed. The more fundamental question from a scientific standpoint is what is consciousness? Nobody has a convincing answer as to how the experience of an apple can arise from a bunch of chemicals and cells wired together in a neural net inside a body.

Why is does modern western science assume that materiality comes first and subjective mental phenomena is a byproduct of brain chemicals? Why can't the latter be true? Or co-arising of both?

It's just a gratuitious assumption in my opinion and a blind-spot for the scientific establishment.

It's weird that this hasn't been said explicitly, but only kind of vaguely gestured as - but you have visions with the noetic quality of truth Daniel was talking about, but *they seem to do with past lives*. So some people have context around them (like they remember things reversed chronologically until they get to the start, and then they keep going backwards until it's an old life).

But even within Buddism there are problems with rebirth
​​​​​​​

from nagarjunas Madhyamaka, by westeroff 

Beth Upton, who trained as a nun with Pa Auk Sayadaw, says that past life memories are generally suspect, even if they feel real, unless they reveal insight into the karmic seed that gave rise to the next rebirth. She gives a basic instruction on how to do the practice of recalling previous lives on her youtube page. 

A lot of the siddhi stuff seems a bit suspect to me. I've met people who claim to read minds and be able to smell diseases and what not, and the statistician training in me just thinks "wow what a very testable claim that you're not going to hold up to scrutiny".

But at the same time I've had weird visions and WILD lucid dreaming when meditation, as well as dreams that "solve" life stuff. I don't think the question should be "is it real?" But really "does this help me live a better life?"

"Ok friend" 

Perhaps it is backwards. Maybe those chemicals, cells and brain networks arise from experience...

But they don't. The topic is controversial. Religious buddhists accept this, because it's in the scripture... sort of.<br />1. Agnostic buddhists experience the perpetuation of Karma, but it is not clear if "rebirth" means that the identity persists, or even if it transmits from one individual to another one (vs. many-to-many). What they definitely experience is that Karma (will, if you like) persists through death (has consequences after someone's death). Take a look at Vipassana: the goal is to experience that "me" is a illusion. How can a non-existing individuum concept be so important in buddhism?<br />2. If I remember correctly, Buddha refused to answer the question of transcendence and individuality. There are of course the Sutras with his past lives, but those are apocryphical. Unfortunately, Buddhism is too vague to have a single interpretation, apart from not being clear if it is a relgion or what.